Design Decision - Adapter Class/Interface
I have person class and I have a project class and I think I want to make the project class an adapter class... does this make sense ?
I can make it an interface but I dont want the person who will implement it to have to implement all the methods in the Project class.
You have a 'person' and you want that person to be a 'project'?
Similar Messages
-
Design Patterns that are used in standard j2se/j2ee classes/interfaces
Hi All,
I am understanding following design patterns (used within standard j2se/j2ee):
Adapter
Facade
Composite
Bridge
Singleton
Observer
Mediator
Proxy
Chain of Responsibility
Flyweight
Builder
Factory Method
Abstract Factory
Prototype
Memento
Template Method
State
Strategy
Command
Interpreter
Decorator
Iterator
Visitor
I want to see if/where these design patterns are used in j2se/j2ee classes/interfaces. i am looking for few examples of standard java classes/interfaces/cases where these design patterns are used by jdk developers.
for e.g.
WindowAdapter class is an example of Adapter DP.
JOptionPane is an exmple of Facade DP.
MouseListener is an example of Observer DP.
Similarly, where can find examples of jdk classes/interfaces of the remaining DPs.
I searched a lot of books, but they explain the DPs by creating their own classes/interfaces.
I would like to see where these DPs are already utilised in std j2se/j2ee
thanks,
Madhu_1980877316 wrote:
I searched a lot of books, but they explain the DPs by creating their own classes/interfaces.
I would like to see where these DPs are already utilised in std j2se/j2eeWell, you can go through the javadocs first, they sometimes mention the pattern used.
Then you can get the sources for the jdk and go through the classes yourself, identifying the patterns. -
Questioning design decision in java.lang.Character
Having a look at the source code for java.lang.Character, I have the Character class explicitly extends Object
I am using jre1.6.0_07 on window XP
Now the question is what is the reason for such a decision and we all know that any class implicitly extends Object class.
public final class Character extends Object implements java.io.Serializable, Comparable<Character> {
}Regards,
Alan Mehio
London, UK
Edited by: alan_mehio on 24-Jul-2009 12:31I cannot answer with anything but personal intuition, and give non-conclusive details:
first this is not a design decision, merely a style decision, since, as you mention, any class implicitly extends directly java.lang.Object if not explicitly extending anything else (and at the bytecode level, the source-level difference is undetectable).
As far as style is concerned, I would have assumed that the whole JDK team is required to strictly follow consistent rules, but different classes suggest otherwise.
Sun's public [Code Conventions for the JavaTM Programming Language|http://java.sun.com/docs/codeconv/html/CodeConventions.doc5.html#2991] do not have an explicit rule about this; section +6.4 Class and Interface Declarations+ provide an example with an extends Object clause, but the rule is not explicit in the text; and the previous section 5.2 does provide an example without this clause...
I went on speculating that the developpers for the Character class had a special intent in mind, as they override Object methods equals() and hascode(), but other class in the same package do the same without the explicit extends Object clause (Void, System, Number). At that step I gave up trying to find a reason other than the developers' own style... -
Class, interface, or enum expected?
Ok I keep getting that error. Here is my java file that it is in.
package server.main.project12.skills;
import java.io.*;
import server.main.project12.*;
public class fireMaking {
public int xpgained = 1;//Change this and the fire xp will be times by that, so 40 time 1 = 40, 40
times 100 = 4000.
public void WalkTo(int x, int y) {
newWalkCmdSteps = (Math.abs((x+y)));
if(newWalkCmdSteps % 1 != 0)
newWalkCmdSteps /= 1;
if(++newWalkCmdSteps > walkingQueueSize) {
println("Warning: WalkTo("+packetType+") command contains too many steps
("+newWalkCmdSteps+").");
newWalkCmdSteps = 0;
int firstStepX = absX;
int tmpFSX = firstStepX;
firstStepX -= mapRegionX*8;
for(i = 1; i < newWalkCmdSteps; i++) {
newWalkCmdX[i] = x;
newWalkCmdY[i] = y;
tmpNWCX[i] = newWalkCmdX;
tmpNWCY[i] = newWalkCmdY[i];
newWalkCmdX[0] = newWalkCmdY[0] = tmpNWCX[0] = tmpNWCY[0] = 0;
int firstStepY = absY;
int tmpFSY = firstStepY;
firstStepY -= mapRegionY*8;
newWalkCmdIsRunning = ((inStream.readSignedByteC() == 1) && playerEnergy > 0);
for(i = 0; i < newWalkCmdSteps; i++) {
newWalkCmdX[i] += firstStepX;
newWalkCmdY[i] += firstStepY;
public int firetimer = 0;
public int firetimers = 0;
public int firetimers1 = 0;
public int firetimers2 = 0;
public int firetimers3 = 0;
public int firetimers4 = 0;
public int firetimers5 = 0;
public int firetimers6 = 0;
public int firetimers7 = 0;
public int firetimers8 = 0;
public int firetimers9 = 0;
public int firetimers10 = 0;
public int firetimers11 = 0;
public int firetimers12 = 0;
public int firetimers13 = 0;
public int firetimers14 = 0;
public int firetimers15 = 0;
public int firetimers16 = 0;
public int firetimers17 = 0;
public int firetimers18 = 0;
public int firetimers19 = 0;
public int previousX = 0;
public int previousY = 0;
public int previousX1 = 0;
public int previousY1 = 0;
public int previousX2 = 0;
public int previousY2 = 0;
public int previousX3 = 0;
public int previousY3 = 0;
public int previousX4 = 0;
public int previousY4 = 0;
public int previousX5 = 0;
public int previousY5 = 0;
public int previousX6 = 0;
public int previousY6 = 0;
public int previousX7 = 0;
public int previousY7 = 0;
public int previousX8 = 0;
public int previousY8 = 0;
public int previousX9 = 0;
public int previousY9 = 0;
public int previousX10 = 0;
public int previousY10 = 0;
public int previousX11 = 0;
public int previousY11 = 0;
public int previousX12 = 0;
public int previousY12 = 0;
public int previousX13 = 0;
public int previousY13 = 0;
public int previousX14 = 0;
public int previousY14 = 0;
public int previousX15 = 0;
public int previousY15 = 0;
public int previousX16 = 0;
public int previousY16 = 0;
public int previousX17 = 0;
public int previousY17 = 0;
public int previousX18 = 0;
public int previousY18 = 0;
public int previousX19 = 0;
public int previousY19 = 0;
public int logID = 0;
public boolean process() {
//FIRE MAKING TIMERS
if(firetimer > 0)
firetimer -= 1;
if(firetimers > 0)
firetimers -= 1;
if(firetimers1 > 0)
firetimers1 -= 1;
if(firetimers3 > 0)
firetimers3 -= 1;
if(firetimers2 > 0)
firetimers2 -= 1;
if(firetimers4 > 0)
firetimers4 -= 1;
if(firetimers5 > 0)
firetimers5 -= 1;
if(firetimers6 > 0)
firetimers6 -= 1;
if(firetimers7 > 0)
firetimers7 -= 1;
if(firetimers8 > 0)
firetimers8 -= 1;
if(firetimers9 > 0)
firetimers9 -= 1;
if(firetimers10 > 0)
firetimers10 -= 1;
if(firetimers11 > 0)
firetimers11 -= 1;
if(firetimers13 > 0)
firetimers13 -= 1;
if(firetimers12 > 0)
firetimers12 -= 1;
if(firetimers14 > 0)
firetimers14 -= 1;
if(firetimers15 > 0)
firetimers15 -= 1;
if(firetimers16 > 0)
firetimers16 -= 1;
if(firetimers17 > 0)
firetimers17 -= 1;
if(firetimers18 > 0)
firetimers18 -= 1;
if(firetimers19 > 0)
firetimers19 -= 1;
if(firetimers == 1)
ItemHandler.addItem(592, previousX, previousY, 1, playerId, false);
ReplaceObject2(previousX, previousY, 6951, 0, 10);
previousX = 0;
previousY = 0;
if(firetimers1 == 1)
ItemHandler.addItem(592, previousX1, previousY1, 1, playerId, false);
ReplaceObject2(previousX1, previousY1, 6951, 0, 10);
previousX1 = 0;
previousY1 = 0;
if(firetimers2 == 1)
ItemHandler.addItem(592, previousX2, previousY1, 1, playerId, false);
ReplaceObject2(previousX2, previousY2, 6951, 0, 10);
previousX2 = 0;
previousY2 = 0;
if(firetimers3 == 1)
ItemHandler.addItem(592, previousX3, previousY3, 1, playerId, false);
ReplaceObject2(previousX3, previousY3, 6951, 0, 10);
previousX3 = 0;
previousY3 = 0;
if(firetimers4 == 1)
ItemHandler.addItem(592, previousX4, previousY4, 1, playerId, false);
ReplaceObject2(previousX4, previousY4, 6951, 0, 10);
previousX4 = 0;
previousY4 = 0;
if(firetimers5 == 1)
ItemHandler.addItem(592, previousX5, previousY5, 1, playerId, false);
ReplaceObject2(previousX5, previousY5, 6951, 0, 10);
previousX5 = 0;
previousY5 = 0;
if(firetimers9 == 1)
ItemHandler.addItem(592, previousX9, previousY9, 1, playerId, false);
ReplaceObject2(previousX9, previousY9, 6951, 0, 10);
previousX9 = 0;
previousY9 = 0;
if(firetimers8 == 1)
ItemHandler.addItem(592, previousX8, previousY8, 1, playerId, false);
ReplaceObject2(previousX8, previousY8, 6951, 0, 10);
previousX8 = 0;
previousY8 = 0;
if(firetimers7 == 1)
ItemHandler.addItem(592, previousX7, previousY7, 1, playerId, false);
ReplaceObject2(previousX7, previousY7, 6951, 0, 10);
previousX7 = 0;
previousY7 = 0;
if(firetimers6 == 1)
ItemHandler.addItem(592, previousX6, previousY6, 1, playerId, false);
ReplaceObject2(previousX6, previousY6, 6951, 0, 10);
previousX6 = 0;
previousY6 = 0;
if(firetimers10== 1)
ItemHandler.addItem(592, previousX10, previousY10, 1, playerId, false);
ReplaceObject2(previousX10, previousY10, 6951, 0, 10);
previousX10 = 0;
previousY10 = 0;
if(firetimers11 == 1)
ItemHandler.addItem(592, previousX11, previousY11, 1, playerId, false);
ReplaceObject2(previousX11, previousY11, 6951, 0, 10);
previousX11 = 0;
previousY11 = 0;
if(firetimers12 == 1)
ItemHandler.addItem(592, previousX12, previousY12, 1, playerId, false);
ReplaceObject2(previousX12, previousY12, 6951, 0, 10);
previousX12 = 0;
previousY12 = 0;
if(firetimers13 == 1)
ItemHandler.addItem(592, previousX13, previousY13, 1, playerId, false);
ReplaceObject2(previousX13, previousY13, 6951, 0, 10);
previousX13 = 0;
previousY13 = 0;
if(firetimers14 == 1)
ItemHandler.addItem(592, previousX14, previousY14, 1, playerId, false);
ReplaceObject2(previousX14, previousY14, 6951, 0, 10);
previousX14 = 0;
previousY14 = 0;
if(firetimers15 == 1)
ItemHandler.addItem(592, previousX15, previousY15, 1, playerId, false);
ReplaceObject2(previousX15, previousY15, 6951, 0, 10);
previousX15 = 0;
previousY15 = 0;
if(firetimers19 == 1)
ItemHandler.addItem(592, previousX19, previousY19, 1, playerId, false);
ReplaceObject2(previousX19, previousY19, 6951, 0, 10);
previousX19 = 0;
previousY19 = 0;
if(firetimers18 == 1)
ItemHandler.addItem(592, previousX18, previousY18, 1, playerId, false);
ReplaceObject2(previousX18, previousY18, 6951, 0, 10);
previousX18 = 0;
previousY18 = 0;
if(firetimers17 == 1)
ItemHandler.addItem(592, previousX17, previousY17, 1, playerId, false);
ReplaceObject2(previousX17, previousY17, 6951, 0, 10);
previousX17 = 0;
previousY17 = 0;
if(firetimers16 == 1)
ItemHandler.addItem(592, previousX16, previousY16, 1, playerId, false);
ReplaceObject2(previousX16, previousY16, 6951, 0, 10);
previousX16 = 0;
previousY16 = 0;
if(firetimer == 1)
if(logID == 1)
addSkillXP((40*xpgained), 11);
removeGroundItem(absX, absY, 1511);
logID = 0;
if(logID == 2)
addSkillXP((60*xpgained), 11);
removeGroundItem(absX, absY, 1521);
logID = 0;
if(logID == 3)
addSkillXP((90*xpgained), 11);
removeGroundItem(absX, absY, 1519);
logID = 0;
if(logID == 4)
addSkillXP((135*xpgained), 11);
removeGroundItem(absX, absY, 1517);
logID = 0;
if(logID == 5)
addSkillXP((202*xpgained), 11);
removeGroundItem(absX, absY, 1515);
logID = 0;
if(logID == 6)
addSkillXP((303*xpgained), 11);
removeGroundItem(absX, absY, 1513);
logID = 0;
WalkTo(-1, 0);
sendMessage("The fire catches, and the logs begin to burn.");
Object(absX, absY, 2732, 0, 10);
firetimer = 0;
updateRequired = true;
appearanceUpdateRequired = true;
if(previousX == 0 && previousY == 0)
previousX = absX;
previousY = absY;
firetimers = 60; //DO NOT CHANGE THIS
viewTo(previousX, previousY);
else
if(previousX1 == 0 && previousY1 == 0)
previousX1 = absX;
previousY1 = absY;
firetimers1 = 60;
viewTo(previousX1, previousY1);
else
if(previousX2 == 0 && previousY2 == 0)
previousX2 = absX;
previousY2 = absY;
firetimers2 = 60;
viewTo(previousX2, previousY2);
else
if(previousX3 == 0 && previousY3 == 0)
previousX3 = absX;
previousY3 = absY;
firetimers3 = 60;
viewTo(previousX3, previousY3);
else
if(previousX4 == 0 && previousY4 == 0)
previousX4 = absX;
previousY4 = absY;
firetimers4 = 60;
viewTo(previousX4, previousY4);
else
if(previousX5 == 0 && previousY5 == 0)
previousX5 = absX;
previousY5 = absY;
firetimers5 = 60;
viewTo(previousX5, previousY5);
else
if(previousX6 == 0 && previousY6 == 0)
previousX6 = absX;
previousY6 = absY;
firetimers6 = 60;
viewTo(previousX6, previousY6);
else
if(previousX7 == 0 && previousY7 == 0)
previousX7 = absX;
previousY7 = absY;
firetimers7 = 60;
viewTo(previousX7, previousY7);
else
if(previousX8 == 0 && previousY8 == 0)
previousX8 = absX;
previousY8 = absY;
firetimers8 = 60;
viewTo(previousX8, previousY8);
else
if(previousX9 == 0 && previousY9 == 0)
previousX9 = absX;
previousY9 = absY;
firetimers9 = 60;
viewTo(previousX9, previousY9);
else
if(previousX10 == 0 && previousY10 == 0)
previousX10 = absX;
previousY10 = absY;
firetimers10 = 60;
viewTo(previousX10, previousY10);
else
if(previousX11 == 0 && previousY11 == 0)
previousX11 = absX;
previousY11 = absY;
firetimers11 = 60;
viewTo(previousX11, previousY11);
else
if(previousX12 == 0 && previousY12 == 0)
previousX12 = absX;
previousY12 = absY;
firetimers12 = 60;
viewTo(previousX12, previousY12);
else
if(previousX13 == 0 && previousY13 == 0)
previousX13 = absX;
previousY13 = absY;
firetimers13 = 60;
viewTo(previousX13, previousY13);
else
if(previousX14 == 0 && previousY14 == 0)
previousX14 = absX;
previousY14 = absY;
firetimers14 = 60;
viewTo(previousX14, previousY14);
else
if(previousX15 == 0 && previousY15 == 0)
previousX15 = absX;
previousY15 = absY;
firetimers15 = 60;
viewTo(previousX15, previousY15);
else
if(previousX16 == 0 && previousY16 == 0)
previousX16 = absX;
previousY16 = absY;
firetimers16 = 60;
viewTo(previousX16, previousY16);
else
if(previousX17 == 0 && previousY17 == 0)
previousX17 = absX;
previousY17 = absY;
firetimers17 = 60;
viewTo(previousX17, previousY17);
else
if(previousX18 == 0 && previousY18 == 0)
previousX18 = absX;
previousY18 = absY;
firetimers18 = 60;
viewTo(previousX18, previousY18);
else
if(previousX19 == 0 && previousY19 == 0)
previousX19 = absX;
previousY19 = absY;
firetimers19 = 60;
viewTo(previousX19, previousY19);
}And this is what my compiler is showing.C:\Users\Matthew\Documents\server.main.project12>javac *.java
Note: stream.java uses or overrides a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
C:\Users\Matthew\Documents\server.main.project12>javac ./skills/*.java
.\skills\firemaking.java:594: class, interface, or enum expected
^
1 error
C:\Users\Matthew\Documents\server.main.project12>pause
Press any key to continue . . .I really need help with this.This error is often caused by improper matching of braces { }.
Solution: Check the matching opening and closing braces.
Worse, the error could be totally invisible! Often, it is the first thing in the file, before package or import declarations
In that situation, it could be caused by a code edited / formatted using a text editor not designed for programming such as Word, which introduces invisible characters in the code.
Solution : In that case, cut and paste the code in a true code editor as Eclipse or NotePad which withdrawing the offending characters.
This error occurs most often in the console (command line), almost never in an IDE. -
Changing a variable in adapter class
Hi,
I've deployed hello world application and I see that there was a variable like "message". And this was defined in EPN assembly file as instance-propery.
<wlevs:adapter id="helloworldAdapter" class="com.bea.wlevs.adapter.example.helloworld.HelloWorldAdapter" >
<wlevs:instance-property name="message" value="HelloWorld - the current time is:"/>
</wlevs:adapter>HelloWorld application works now.
I want to change value of message variable from out of application. I could this wishes via wlevs.Admin but I am not:
java -jar wlevsadmin.jar -url service:jmx:msarmi://localhost:9002/jndi/jmxconnector -username wlevs -password xxx GET -pretty -mbean com.bea.wlevs:Name=helloworldAdapter,Type=Adapter,Application=fuat_deneme
MBeanName: "com.bea.wlevs:Name=helloworldAdapter,Type=Adapter,Application=fuat_deneme"
InstanceProperties:
message = HelloWorld - the current time is:
Name: helloworldAdapter
NotificationInfo: [Ljavax.management.MBeanNotificationInfo;@2b20bf2c
ObjectName: com.bea.wlevs:Name=helloworldAdapter,Type=Adapter,Application=fuat_deneme
PlaybackConfiguration:
PlayingBack: false
Provider:
RecordConfiguration:
RecordPlayback: com.bea.wlevs:Name=helloworldAdapter,Type=RecordPlayback,Application=fuat_deneme
Recording: false
StageClassName: com.bea.wlevs.adapter.example.helloworld.HelloWorldAdapter
Type: AdapterOK. When I want to change :
java -jar wlevsadmin.jar -url service:jmx:msarmi://localhost:9002/jndi/jmxconnector -username wlevs -password xxx SET -mbean com.bea.wlevs:Name=helloworldAdapter,Type=Adapter,Application=fuat_deneme -property message "aaa"
Property Name and value not valid for the MBean. Value aaa for parameter[message].java.lang.IllegalArgumentException: Unable to find the attribute: message in the attribute list of the class: null
Description:
Sets property values for Administration MBeans or Local Configuration MBeans. This command cannot be used for Runtime MBeans.
Usage:
java wlevs.Admin
[-url | -listenAddress <host-name> -listenPort <port>]
-username <username> -password <password>
SET {-type <mbeanType>|-mbean <objectName>} [-property <property> [<value>]]...
Where:
-type = Sets the properties for all MBeans of the specified type.
-mbean = Fully qualified object name of an MBean.
-property = The name of the property to be set.
<value> = The value to be set.
java wlevs.Admin -url service:jmx:msarmi://localhost:9002/jndi/jmxconnector -username wlevs -password wlevs SET -type Server -property StdoutSeverityLevel 64
java wlevs.Admin -url service:jmx:msarmi://localhost:9002/jndi/jmxconnector -username wlevs -password wlevs SET -mbean mydomain:Location=oamserver,Name=myserver,Type=ServerConfig -property StdoutSeverityLevel 64How can I change a variable of an adapter class in runtime?I did your suggestion but I am getting ClassNotFound error. However I already specified that as " com.bea.wlevs.management.configuration" in MANIFEST. Also, I can import "com.bea.wlevs.management.configuration.spi.ConfigurationMBeanFactory" class in any our class.
java.lang.IllegalArgumentException: Cannot find class [com.bea.wlevs.management.configuration.spi.ConfigurationMBeanFactory]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:480)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:264)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:423)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:729)
at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext.access$1600(AbstractDelegatedExecutionApplicationContext.java:69)
at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext$4.run(AbstractDelegatedExecutionApplicationContext.java:355)
at org.springframework.osgi.util.internal.PrivilegedUtils.executeWithCustomTCCL(PrivilegedUtils.java:85)
at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext.completeRefresh(AbstractDelegatedExecutionApplicationContext.java:320)
at org.springframework.osgi.extender.internal.dependencies.startup.DependencyWaiterApplicationContextExecutor$CompleteRefreshTask.run(DependencyWaiterApplicationContextExecutor.java:139)
at org.springframework.scheduling.commonj.DelegatingWork.run(DelegatingWork.java:62)
at weblogic.work.commonj.CommonjWorkManagerImpl$WorkWithListener.run(CommonjWorkManagerImpl.java:196)
at weblogic.work.SelfTuningWorkManagerImpl$WorkAdapterImpl.run(SelfTuningWorkManagerImpl.java:528)
at weblogic.work.ExecuteThread.execute(ExecuteThread.java:201)
at weblogic.work.ExecuteThread.run(ExecuteThread.java:173)
Caused By: org.springframework.beans.TypeMismatchException: Failed to convert property value of type [java.lang.String] to required type [java.lang.Class[]] for property 'interfaces'; nested exception is java.lang.IllegalArgumentException: Cannot find class [com.bea.wlevs.management.configuration.spi.ConfigurationMBeanFactory]
at org.springframework.beans.BeanWrapperImpl.convertForProperty(BeanWrapperImpl.java:391)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.convertForProperty(AbstractAutowireCapableBeanFactory.java:1289)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1250)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1010)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:472)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:264)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:423)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:729)
at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext.access$1600(AbstractDelegatedExecutionApplicationContext.java:69)
at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext$4.run(AbstractDelegatedExecutionApplicationContext.java:355)
at org.springframework.osgi.util.internal.PrivilegedUtils.executeWithCustomTCCL(PrivilegedUtils.java:85)
at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext.completeRefresh(AbstractDelegatedExecutionApplicationContext.java:320)
at org.springframework.osgi.extender.internal.dependencies.startup.DependencyWaiterApplicationContextExecutor$CompleteRefreshTask.run(DependencyWaiterApplicationContextExecutor.java:139)
at org.springframework.scheduling.commonj.DelegatingWork.run(DelegatingWork.java:62)
at weblogic.work.commonj.CommonjWorkManagerImpl$WorkWithListener.run(CommonjWorkManagerImpl.java:196)
at weblogic.work.SelfTuningWorkManagerImpl$WorkAdapterImpl.run(SelfTuningWorkManagerImpl.java:528)
at weblogic.work.ExecuteThread.execute(ExecuteThread.java:201)
at weblogic.work.ExecuteThread.run(ExecuteThread.java:173)
Caused By: java.lang.IllegalArgumentException: Cannot find class [com.bea.wlevs.management.configuration.spi.ConfigurationMBeanFactory]
at org.springframework.util.ClassUtils.resolveClassName(ClassUtils.java:233)
at org.springframework.beans.propertyeditors.ClassArrayEditor.setAsText(ClassArrayEditor.java:66)
at org.springframework.beans.TypeConverterDelegate.doConvertTextValue(TypeConverterDelegate.java:382)
at org.springframework.beans.TypeConverterDelegate.doConvertValue(TypeConverterDelegate.java:358)
at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:173)
at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:138)
at org.springframework.beans.BeanWrapperImpl.convertForProperty(BeanWrapperImpl.java:386)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.convertForProperty(AbstractAutowireCapableBeanFactory.java:1289)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1250)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1010)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:472)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:264)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:423)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:728)
at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext.access$1600(AbstractDelegatedExecutionApplicationContext.java:69)
at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext$4.run(AbstractDelegatedExecutionApplicationContext.java:355)
at org.springframework.osgi.util.internal.PrivilegedUtils.executeWithCustomTCCL(PrivilegedUtils.java:85)
at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext.completeRefresh(AbstractDelegatedExecutionApplicationContext.java:320)
at org.springframework.osgi.extender.internal.dependencies.startup.DependencyWaiterApplicationContextExecutor$CompleteRefreshTask.run(DependencyWaiterApplicationContextExecutor.java:136)
at org.springframework.scheduling.commonj.DelegatingWork.run(DelegatingWork.java:61)
at weblogic.work.commonj.CommonjWorkManagerImpl$WorkWithListener.run(CommonjWorkManagerImpl.java:196)
at weblogic.work.SelfTuningWorkManagerImpl$WorkAdapterImpl.run(SelfTuningWorkManagerImpl.java:528)
at weblogic.work.ExecuteThread.execute(ExecuteThread.java:201)
at weblogic.work.ExecuteThread.run(ExecuteThread.java:173)
Caused By: java.lang.ClassNotFoundException: com.bea.wlevs.management.configuration.spi.ConfigurationMBeanFactory not found from bundle [AfterJMS_2]
at org.springframework.osgi.util.BundleDelegatingClassLoader.findClass(BundleDelegatingClassLoader.java:103)
at org.springframework.osgi.util.BundleDelegatingClassLoader.loadClass(BundleDelegatingClassLoader.java:156)
at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
at org.springframework.util.ClassUtils.forName(ClassUtils.java:211)
at org.springframework.util.ClassUtils.resolveClassName(ClassUtils.java:230)
at org.springframework.beans.propertyeditors.ClassArrayEditor.setAsText(ClassArrayEditor.java:66)
at org.springframework.beans.TypeConverterDelegate.doConvertTextValue(TypeConverterDelegate.java:382)
at org.springframework.beans.TypeConverterDelegate.doConvertValue(TypeConverterDelegate.java:358)
at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:173)
at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:138)
at org.springframework.beans.BeanWrapperImpl.convertForProperty(BeanWrapperImpl.java:386)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.convertForProperty(AbstractAutowireCapableBeanFactory.java:1289)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1250)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1011)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:472)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:264)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:423)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:729)
at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext.access$1600(AbstractDelegatedExecutionApplicationContext.java:69)
at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext$4.run(AbstractDelegatedExecutionApplicationContext.java:355)
at org.springframework.osgi.util.internal.PrivilegedUtils.executeWithCustomTCCL(PrivilegedUtils.java:85)
at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext.completeRefresh(AbstractDelegatedExecutionApplicationContext.java:320)
at org.springframework.osgi.extender.internal.dependencies.startup.DependencyWaiterApplicationContextExecutor$CompleteRefreshTask.run(DependencyWaiterApplicationContextExecutor.java:139)
at org.springframework.scheduling.commonj.DelegatingWork.run(DelegatingWork.java:62)
at weblogic.work.commonj.CommonjWorkManagerImpl$WorkWithListener.run(CommonjWorkManagerImpl.java:196)
at weblogic.work.SelfTuningWorkManagerImpl$WorkAdapterImpl.run(SelfTuningWorkManagerImpl.java:528)
at weblogic.work.ExecuteThread.execute(ExecuteThread.java:201)
at weblogic.work.ExecuteThread.run(ExecuteThread.java:173)
Caused By: java.lang.ClassNotFoundException: com.bea.wlevs.management.configuration.spi.ConfigurationMBeanFactory
at org.eclipse.osgi.internal.loader.BundleLoader.findClassInternal(BundleLoader.java:494)
at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:410)
at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:398)
at org.eclipse.osgi.internal.baseadaptor.DefaultClassLoader.loadClass(DefaultClassLoader.java:123)
at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
at org.eclipse.osgi.internal.loader.BundleLoader.loadClass(BundleLoader.java:326)
at org.eclipse.osgi.framework.internal.core.BundleHost.loadClass(BundleHost.java:231)
at org.eclipse.osgi.framework.internal.core.AbstractBundle.loadClass(AbstractBundle.java:1193)
at org.springframework.osgi.util.BundleDelegatingClassLoader.findClass(BundleDelegatingClassLoader.java:99)
at org.springframework.osgi.util.BundleDelegatingClassLoader.loadClass(BundleDelegatingClassLoader.java:156)
at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
at org.springframework.util.ClassUtils.forName(ClassUtils.java:211)
at org.springframework.util.ClassUtils.resolveClassName(ClassUtils.java:230)
at org.springframework.beans.propertyeditors.ClassArrayEditor.setAsText(ClassArrayEditor.java:66)
at org.springframework.beans.TypeConverterDelegate.doConvertTextValue(TypeConverterDelegate.java:382)
at org.springframework.beans.TypeConverterDelegate.doConvertValue(TypeConverterDelegate.java:358)
at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:173)
at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:138)
at org.springframework.beans.BeanWrapperImpl.convertForProperty(BeanWrapperImpl.java:386)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.convertForProperty(AbstractAutowireCapableBeanFactory.java:1289)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1250)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1011)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:472)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:264)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:423)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:729)
at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext.access$1600(AbstractDelegatedExecutionApplicationContext.java:69)
at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext$4.run(AbstractDelegatedExecutionApplicationContext.java:355)
at org.springframework.osgi.util.internal.PrivilegedUtils.executeWithCustomTCCL(PrivilegedUtils.java:85)
at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext.completeRefresh(AbstractDelegatedExecutionApplicationContext.java:320)
at org.springframework.osgi.extender.internal.dependencies.startup.DependencyWaiterApplicationContextExecutor$CompleteRefreshTask.run(DependencyWaiterApplicationContextExecutor.java:139)
at org.springframework.scheduling.commonj.DelegatingWork.run(DelegatingWork.java:62)
at weblogic.work.commonj.CommonjWorkManagerImpl$WorkWithListener.run(CommonjWorkManagerImpl.java:196)
at weblogic.work.SelfTuningWorkManagerImpl$WorkAdapterImpl.run(SelfTuningWorkManagerImpl.java:528)
at weblogic.work.ExecuteThread.execute(ExecuteThread.java:201)
at weblogic.work.ExecuteThread.run(ExecuteThread.java:173) -
WebDynpro Method from a Class Interface?
Is possible to call a webdynpro method from a class interface that is register in the WDDOINIT of the same WEBDYNPRO component?
I register my custom webdynpro screen into FPM_OIF_COMPONENT, now when I execute a FPM action my WebDynpro receives the action but ofcourse WDDOINIT doesn't get triggered again. I need to call my webdynpro code in the class interface so I can update my custom screen.
SAP does that in their standard screen, Can I do that?
Jason PVAs Matt pointed out, your questions indicate that you should start from the basics, then as your knowledge enlarges, go and familarize with more advanced concepts of ABAP Objects. Once you feel a bit comfortable with that, go for BADIs and read a bit about that too.
In my opinion the best start is to read some book, which covers most of ABAP OO concepts. Personally I would recommend [ABAP Objects: ABAP Programming in SAP NetWeaver|http://www.sap-press.com/product.cfm?account=&product=H1934] as I like this author and had his previous book. This would give you strong foundations of what is going on here. Eventually you will often want to refresh some concepts so you have everything you need in one spot (book).
Of course if want to save some money, simply look for articles/blogs/wikis in SDN or search in Google. There are plenty of these.
For start I suggest these series of videoblogs [Basic ABAP OO eLearnings|http://www.sdn.sap.com/irj/scn/weblogs;jsessionid=(J2EE3414800)ID1160600550DB10016261778120999663End?blog=/pub/wlg/15408]
This will give you rough idea how the OO design should be done.
Regards
Marcin -
Hi ,
I have a fundamental doubt regarding Abstract Class & Interface!!!
What is their real benefit...whether we implement an interface or extend an Abstract class we have to write the code for the abstract method in the concrete class.Then where the benefit remained....
And it is said that Abstract class provide default behaviour...what is the actual meaning of that?
Thanks & Regards
SantoshIn this section we will redesign our OneRowNim game to fit within a hierarchy of classes of two-player games. There are many games that characteristically involve two players: checkers, chess, tic-tac-toe, guessing games, and so forth. However, there are also many games that involve just one player: blackjack, solitaire, and others. There are also games that involve two or more players, such as many card games. Thus, our redesign of OneRowNim as part of a two-player game hierarchy will not be our last effort to design a hierarchy of game-playing classes. We will certainly redesign things as we learn new Java language constructs and as we try to extend our game library to other kinds of games.
This case study will illustrate how we can apply inheritance and polymorphism, as well as other object-oriented design principles. The justification for revising OneRowNim at this point is to make it easier to design and develop other two-player games. As we have seen, one characteristic of class hierarchies is that more general attributes and methods are defined in top-level classes. As one proceeds down the hierarchy, the methods and attributes become more specialized. Creating a subclass is a matter of specializing a given class.
8.6.1. Design Goals
One of our design goals is to revise the OneRowNim game so that it fits into a hierarchy of two-player games. One way to do this is to generalize the OneRowNim game by creating a superclass that contains those attributes and methods that are common to all two-player games. The superclass will define the most general and generic elements of two-player games. All two-player games, including OneRowNim, will be defined as subclasses of this top-level superclass and will inherit and possibly override its public and protected variables and methods. Also, our top-level class will contain certain abstract methods, whose implementations will be given in OneRowNim and other subclasses.
Generic superclass
A second goal is to design a class hierarchy that makes it possible for computers to play the game, as well as human users. Thus, for a given two-player game, it should be possible for two humans to play each other, or for two computers to play each other, or for a human to play against a computer. This design goal will require that our design exhibit a certain amount of flexibility. As we shall see, this is a situation in which Java interfaces will come in handy.
[Page 376]
Another important goal is to design a two-player game hierarchy that can easily be used with a variety of different user interfaces, including command-line interfaces and GUIs. To handle this feature, we will develop Java interfaces to serve as interfaces between our two-player games and various user interfaces.
8.6.2. Designing the TwoPlayerGame Class
To begin revising the design of the OneRowNim game, we first need to design a top-level class, which we will call the TwoPlayerGame class. What variables and methods belong in this class? One way to answer this question is to generalize our current version of OneRowNim by moving any variables and methods that apply to all two-player games up to the TwoPlayerGame class. All subclasses of TwoPlayerGamewhich includes the OneRowNim classwould inherit these elements. Figure 8.18 shows the current design of OneRowNim.
Figure 8.18. The current OneRowNim class.
What variables and methods should we move up to the TwoPlayerGame class? Clearly, the class constants, PLAYER_ONE and PLAYER_TWO, apply to all two-player games. These should be moved up. On the other hand, the MAX_PICKUP and MAX_STICKS constants apply just to the OneRowNim game. They should remain in the OneRowNim class.
The nSticks instance variable is a variable that only applies to the OneRowNim game but not to other two-player games. It should stay in the OneRowNim class. On the other hand, the onePlaysNext variable applies to all two-player games, so we will move it up to the TwoPlayerGame class.
Because constructors are not inherited, all of the constructor methods will remain in the OneRowNim class. The instance methods, takeSticks() and getSticks(), are specific to OneRowNim, so they should remain there. However, the other methods, getPlayer(), gameOver(), getWinner(), and reportGameState(), are methods that would be useful to all two-player games. Therefore these methods should be moved up to the superclass. Of course, while these methods can be defined in the superclass, some of them can only be implemented in subclasses. For example, the reportGameState() method reports the current state of the game, so it has to be implemented in OneRowNim. Similarly, the getWinner() method defines how the winner of the game is determined, a definition that can only occur in the subclass. Every two-player game needs methods such as these. Therefore, we will define these methods as abstract methods in the superclass. The intention is that TwoPlayerGame subclasses will provide game-specific implementations for these methods.
[Page 377]
Constructors are not inherited
Given these considerations, we come up with the design shown in Figure 8.19. The design shown in this figure is much more complex than the designs used in earlier chapters. However, the complexity comes from combining ideas already discussed in previous sections of this chapter, so don't be put off by it.
Figure 8.19. TwoPlayerGame is the superclass for OneRowNim and other two-player games.
To begin with, note that we have introduced two Java interfaces into our design in addition to the TwoPlayerGame superclass. As we will show, these interfaces lead to a more flexible design and one that can easily be extended to incorporate new two-player games. Let's take each element of this design separately.
[Page 378]
8.6.3. The TwoPlayerGame Superclass
As we have stated, the purpose of the TwoPlayerGame class is to serve as the superclass for all two-player games. Therefore, it should define the variables and methods shared by two-player games.
The PLAYER_ONE, PLAYER_TWO, and onePlaysNext variables and the getPlayer(), setPlayer(), and changePlayer() methods have been moved up from the OneRowNim class. Clearly, these variables and methods apply to all two-player games. Note that we have also added three new variables, nComputers, computer1, computer2, and their corresponding methods, getNComputers() and addComputerPlayer(). We will use these elements to give our games the capability to be played by computer programs. Because we want all of our two-player games to have this capability, we define these variables and methods in the superclass rather than in OneRowNim and subclasses of TwoPlayerGame.
Note that the computer1 and computer2 variables are declared to be of type IPlayer. IPlayer is an interface containing a single method declaration, the makeAMove() method:
public interface IPlayer {
public String makeAMove(String prompt);
Why do we use an interface here rather than some type of game-playing object? This is a good design question. Using an interface here makes our design more flexible and extensible because it frees us from having to know the names of the classes that implement the makeAMove() method. The variables computer1 and computer2 will be assigned objects that implement IPlayer via the addComputerPlayer() method.
Game-dependent algorithms
The algorithms used in the various implementations of makeAMove() are game-dependentthey depend on the particular game being played. It would be impossible to define a game playing object that would suffice for all two-player games. Instead, if we want an object that plays OneRowNim, we would define a OneRowNimPlayer and have it implement the IPlayer interface. Similarly, if we want an object that plays checkers, we would define a CheckersPlayer and have it implement the IPlayer interface. By using an interface here, our TwoPlayerGame hierarchy can deal with a wide range of differently named objects that play games, as long as they implement the IPlayer interface. Using the IPlayer interface adds flexibility to our game hierarchy and makes it easier to extend it to new, yet undefined, classes. We will discuss the details of how to design a game player in Section 8.6.7.
The IPlayer interface
Turning now to the methods defined in TwoPlayerGame, we have already seen implementations of getPlayer(), setPlayer(), and changePlayer() in the OneRowNim class. We will just move those implementations up to the superclass. The getNComputers() method is the assessor method for the nComputers variable, and its implementation is routine. The addComputerPlayer() method adds a computer player to the game. Its implementation is as follows:
[Page 379]
public void addComputerPlayer(IPlayer player) {
if (nComputers == 0)
computer2 = player;
else if (nComputers == 1)
computer1 = player;
else
return; // No more than 2 players
++nComputers;
As we noted earlier, the classes that play the various TwoPlayerGames must implement the IPlayer interface. The parameter for this method is of type IPlayer. The algorithm we use checks the current value of nComputers. If it is 0, which means that this is the first IPlayer added to the game, the player is assigned to computer2. This allows the human user to be associated with PLAYERONE if this is a game between a computer and a human user.
If nComputers equals 1, which means that we are adding a second IPlayer to the game, we assign that player to computer1. In either of these cases, we increment nComputers. Note what happens if nComputers is neither 1 nor 2. In that case, we simply return without adding the IPlayer to the game and without incrementing nComputers. This, in effect, limits the number of IPlayers to two. (A more sophisticated design would throw an exception to report an error. but we will leave that for a subsequent chapter.)
The addComputerPlayer() method is used to initialize a game after it is first created. If this method is not called, the default assumption is that nComputers equals zero and that computer1 and computer2 are both null. Here's an example of how it could be used:
OneRowNim nim = new OneRowNim(11); // 11 sticks
nim.add(new NimPlayer(nim)); // 2 computer players
nim.add(new NimPlayerBad(nim));
Note that the NimPlayer() constructor takes a reference to the game as its argument. Clearly, our design should not assume that the names of the IPlayer objects would be known to the TwoPlayerGame superclass. This method allows the objects to be passed in at runtime. We will discuss the details of NimPlayerBad in Section 8.6.7.
The getrules() method is a new method whose purpose is to return a string that describes the rules of the particular game. This method is implemented in the TwoPlayerGame class with the intention that it will be overridden in the various subclasses. For example, its implementation in TwoPlayerGame is:
public String getRules() {
return "The rules of this game are: ";
Overriding a method
[Page 380]
and its redefinition in OneRowNim is:
public String getRules() {
return "\n*** The Rules of One Row Nim ***\n" +
"(1) A number of sticks between 7 and " + MAX_STICKS +
" is chosen.\n" +
"(2) Two players alternate making moves.\n" +
"(3) A move consists of subtracting between 1 and\n\t" +
MAX_PICKUP +
" sticks from the current number of sticks.\n" +
"(4) A player who cannot leave a positive\n\t" +
" number of sticks for the other player loses.\n";
The idea is that each TwoPlayerGame subclass will take responsibility for specifying its own set of rules in a form that can be displayed to the user.
You might recognize that defining geTRules() in the superclass and allowing it to be overridden in the subclasses is a form of polymorphism. It follows the design of the toString() method, which we discussed earlier. This design will allow us to use code that takes the following form:
TwoPlayerGame game = new OneRowNim();
System.out.println(game.getRules());
Polymorphism
In this example the call to getrules() is polymorphic. The dynamic-binding mechanism is used to invoke the getrules() method defined in the OneRowNim class.
The remaining methods in TwoPlayerGame are defined abstractly. The gameOver() and getWinner() methods are both game-dependent methods. That is, the details of their implementations depend on the particular TwoPlayerGame subclass in which they are implemented.
This is good example of how abstract methods should be used in designing a class hierarchy. We give abstract definitions in the superclass and leave the detailed implementations up to the individual subclasses. This allows the different subclasses to tailor the implementations to their particular needs, while allowing all subclasses to share a common signature for these tasks. This enables us to use polymorphism to create flexible, extensible class hierarchies.
Figure 8.20 shows the complete implementation of the abstract TwoPlayerGame class. We have already discussed the most important details of its implementation.
Figure 8.20. The TwoPlayerGame class
(This item is displayed on page 381 in the print version)
public abstract class TwoPlayerGame {
public static final int PLAYER_ONE = 1;
public static final int PLAYER_TWO = 2;
protected boolean onePlaysNext = true;
protected int nComputers = 0; // How many computers
// Computers are IPlayers
protected IPlayer computer1, computer2;
public void setPlayer(int starter) {
if (starter == PLAYER_TWO)
onePlaysNext = false;
else onePlaysNext = true;
} // setPlayer()
public int getPlayer() {
if (onePlaysNext)
return PLAYER_ONE;
else return PLAYER_TWO;
} // getPlayer()
public void changePlayer() {
onePlaysNext = !onePlaysNext;
} // changePlayer()
public int getNComputers() {
return nComputers;
} // getNComputers()
public String getRules() {
return "The rules of this game are: ";
} // getRules()
public void addComputerPlayer(IPlayer player) {
if (nComputers == 0)
computer2 = player;
else if (nComputers == 1)
computer1 = player;
else
return; // No more than 2 players
++nComputers;
} // addComputerPlayer()
public abstract boolean gameOver(); // Abstract Methods
public abstract String getWinner();
} // TwoPlayerGame class
Effective Design: Abstract Methods
Abstract methods allow you to give general definitions in the superclass and leave the implementation details to the different subclasses.
[Page 381]
8.6.4. The CLUIPlayableGame Interface
We turn now to the two interfaces shown in Figure 8.19. Taken together, the purpose of these interfaces is to create a connection between any two-player game and a command-line user interface (CLUI). The interfaces provide method signatures for the methods that will implement the details of the interaction between a TwoPlayerGame and a UserInterface. Because the details of this interaction vary from game to game, it is best to leave the implementation of these methods to the games themselves.
Note that CLUIPlayableGame extends the IGame interface. The IGame interface contains two methods that are used to define a standard form of communication between the CLUI and the game. The getGamePrompt() method defines the prompt used to signal the user for a move of some kindfor example, "How many sticks do you take (1, 2, or 3)?" And the reportGameState() method defines how the game will report its current statefor example, "There are 11 sticks remaining." CLUIPlayableGame adds the play() method to these two methods. As we will see shortly, the play() method contains the code that will control the playing of the game.
[Page 382]
Extending an interface
The source code for these interfaces is very simple:
public interface CLUIPlayableGame extends IGame {
public abstract void play(UserInterface ui);
public interface IGame {
public String getGamePrompt();
public String reportGameState();
} // IGame
Note that the CLUIPlayableGame interface extends the IGame interface. A CLUIPlayableGame is a game that can be played through a CLUI. The purpose of its play() method is to contain the game-dependent control loop that determines how the game is played via a user interface (UI). In pseudocode, a typical control loop for a game would look something like the following:
Initialize the game.
While the game is not over
Report the current state of the game via the UI.
Prompt the user (or the computer) to make a move via the UI.
Get the user's move via the UI.
Make the move.
Change to the other player.
The play loop sets up an interaction between the game and the UI. The UserInterface parameter allows the game to connect directly to a particular UI. To allow us to play our games through a variety of UIs, we define UserInterface as the following Java interface:
public interface UserInterface {
public String getUserInput();
public void report(String s);
public void prompt(String s);
Any object that implements these three methods can serve as a UI for one of our TwoPlayerGames. This is another example of the flexibility of using interfaces in object-oriented design.
To illustrate how we use UserInterface, let's attach it to our KeyboardReader class, thereby letting a KeyboardReader serve as a CLUI for TwoPlayerGames. We do this simply by implementing this interface in the KeyboardReader class, as follows:
public class KeyboardReader implements UserInterface
[Page 383]
As it turns out, the three methods listed in UserInterface match three of the methods in the current version of KeyboardReader. This is no accident. The design of UserInterface was arrived at by identifying the minimal number of methods in KeyboardReader that were needed to interact with a TwoPlayerGame.
Effective Design: Flexibility of Java Interfaces
A Java interface provides a means of associating useful methods with a variety of different types of objects, leading to a more flexible object-oriented design.
The benefit of defining the parameter more generally as a UserInterface instead of as a KeyboardReader is that we will eventually want to allow our games to be played via other kinds of command-line interfaces. For example, we might later define an Internet-based CLUI that could be used to play OneRowNim among users on the Internet. This kind of extensibilitythe ability to create new kinds of UIs and use them with TwoPlayerGamesis another important design feature of Java interfaces.
Generality principle
Effective Design: Extensibility and Java Interfaces
Using interfaces to define useful method signatures increases the extensibility of a class hierarchy.
As Figure 8.19 shows, OneRowNim implements the CLUIPlayableGame interface, which means it must supply implementations of all three abstract methods: play(), getGamePrompt(), and reportGameState().
8.6.5. Object-Oriented Design: Interfaces or Abstract Classes?
Why are these methods defined in interfaces? Couldn't we just as easily define them in the TwoPlayerGame class and use inheritance to extend them to the various game subclasses? After all, isn't the net result the same, namely, that OneRowNim must implement all three methods.
These are very good design questions, exactly the kinds of questions one should ask when designing a class hierarchy of any sort. As we pointed out in the Animal example earlier in the chapter, you can get the same functionality from an abstract interface and an abstract superclass method. When should we put the abstract method in the superclass, and when does it belong in an interface? A very good discussion of these and related object-oriented design issues is available in Java Design, 2nd Edition, by Peter Coad and Mark Mayfield (Yourdan Press, 1999). Our discussion of these issues follows many of the guidelines suggested by Coad and Mayfield.
Interfaces vs. abstract methods
We have already seen that using Java interfaces increases the flexibility and extensibility of a design. Methods defined in an interface exist independently of a particular class hierarchy. By their very nature, interfaces can be attached to any class, and this makes them very flexible to use.
Flexibility of interfaces
Another useful guideline for answering this question is that the superclass should contain the basic common attributes and methods that define a certain type of object. It should not necessarily contain methods that define certain roles that the object plays. For example, the gameOver() and getWinner() methods are fundamental parts of the definition of a TwoPlayerGame. One cannot define a game without defining these methods. By contrast, methods such as play(), getGamePrompt(), and reportGameState() are important for playing the game but they do not contribute in the same way to the game's definition. Thus these methods are best put into an interface. Therefore, one important design guideline is:
[Page 384]
Effective Design: Abstract Methods
Methods defined abstractly in a superclass should contribute in a fundamental way to the basic definition of that type of object, not merely to one of its roles or its functionality.
8.6.6. The Revised OneRowNim Class
Figure 8.21 provides a listing of the revised OneRowNim class, one that fits into the TwoPlayerGame class hierarchy. Our discussion in this section will focus on the features of the game that are new or revised.
Figure 8.21. The revised OneRowNim class, Part I.
(This item is displayed on page 385 in the print version)
public class OneRowNim extends TwoPlayerGame implements CLUIPlayableGame {
public static final int MAX_PICKUP = 3;
public static final int MAX_STICKS = 11;
private int nSticks = MAX_STICKS;
public OneRowNim() { } // Constructors
public OneRowNim(int sticks) {
nSticks = sticks;
} // OneRowNim()
public OneRowNim(int sticks, int starter) {
nSticks = sticks;
setPlayer(starter);
} // OneRowNim()
public boolean takeSticks(int num) {
if (num < 1 || num > MAX_PICKUP || num > nSticks)
return false; // Error
else // Valid move
{ nSticks = nSticks - num;
return true;
} // else
} // takeSticks()
public int getSticks() {
return nSticks;
} // getSticks()
public String getRules() {
return "\n*** The Rules of One Row Nim ***\n" +
"(1) A number of sticks between 7 and " + MAX_STICKS +
" is chosen.\n" +
"(2) Two players alternate making moves.\n" +
"(3) A move consists of subtracting between 1 and\n\t" +
MAX_PICKUP + " sticks from the current number of sticks.\n" +
"(4) A player who cannot leave a positive\n\t" +
" number of sticks for the other player loses.\n";
} // getRules()
public boolean gameOver() { /*** From TwoPlayerGame */
return (nSticks <= 0);
} // gameOver()
public String getWinner() { /*** From TwoPlayerGame */
if (gameOver()) //{
return "" + getPlayer() + " Nice game.";
return "The game is not over yet."; // Game is not over
} // getWinner()
The gameOver() and getWinner() methods, which are nowinherited from the TwoPlayerGame superclass, are virtually the same as in the previous version. One small change is that getWinner() now returns a String instead of an int. This makes the method more generally useful as a way of identifying the winner for all TwoPlayerGames.
Similarly, the getGamePrompt() and reportGameState() methods merely encapsulate functionality that was present in the earlier version of the game. In our earlier version the prompts to the user were generated directly by the main program. By encapsulating this information in an inherited method, we make it more generally useful to all TwoPlayerGames.
Inheritance and generality
The major change to OneRowNim comes in the play() method, which controls the playing of OneRowNim (Fig. 8.22). Because this version of the game incorporates computer players, the play loop is a bit more complex than in earlier versions of the game. The basic idea is still the same: The method loops until the game is over. On each iteration of the loop, one or the other of the two players, PLAYER_ONE or PLAYER_TWO, takes a turn making a movethat is, deciding how many sticks to pick up. If the move is a legal move, then it becomes the other player's turn.
Figure 8.22. The revised OneRowNim class, Part II.
(This item is displayed on page 386 in the print version)
/** From CLUIPlayableGame */
public String getGamePrompt() {
return "\nYou can pick up between 1 and " +
Math.min(MAX_PICKUP,nSticks) + " : ";
} // getGamePrompt()
public String reportGameState() {
if (!gameOver())
return ("\nSticks left: " + getSticks() +
" Who's turn: Player " + getPlayer());
else
return ("\nSticks left: " + getSticks() +
" Game over! Winner is Player " + getWinner() +"\n");
} // reportGameState()
public void play(UserInterface ui) { // From CLUIPlayableGame interface
int sticks = 0;
ui.report(getRules());
if (computer1 != null)
ui.report("\nPlayer 1 is a " + computer1.toString());
if (computer2 != null)
ui.report("\nPlayer 2 is a " + computer2.toString());
while(!gameOver()) {
IPlayer computer = null; // Assume no computers
ui.report(reportGameState());
switch(getPlayer()) {
case PLAYER_ONE: // Player 1's turn
computer = computer1;
break;
case PLAYER_TWO: // Player 2's turn
computer = computer2;
break;
} // cases
if (computer != null) { // If computer's turn
sticks = Integer.parseInt(computer.makeAMove(""));
ui.report(computer.toString() + " takes " + sticks + " sticks.\n");
} else { // otherwise, user's turn
ui.prompt(getGamePrompt());
sticks =
Integer.parseInt(ui.getUserInput()); // Get user's move
if (takeSticks(sticks)) // If a legal move
changePlayer();
} // while
ui.report(reportGameState()); // The game is now over
} // play()
} // OneRowNim class
Let's look now at how the code decides whether it is a computer's turn to move or a human player's turn. Note that at the beginning of the while loop, it sets the computer variable to null. It then assigns computer a value of either computer1 or computer2, depending on whose turn it is. But recall that one or both of these variables may be null, depending on how many computers are playing the game. If there are no computers playing the game, then both variables will be null. If only one computer is playing, then computer1 will be null. This is determined during initialization of the game, when the addComputerPlayer() is called. (See above.)
In the code following the switch statement, if computer is not null, then we call computer.makeAMove(). As we know, the makeAMove() method is part of the IPlayer interface. The makeAMove() method takes a String parameter that is meant to serve as a prompt, and returns a String that is meant to represent the IPlayer's move:
public interface IPlayer {
public String makeAMove(String prompt);
[Page 385]
In OneRowNim the "move" is an integer, representing the number of sticks the player picks. Therefore, in play() OneRowNim has to convert the String into an int, which represents the number of sticks the IPlayer picks up.
On the other hand, if computer is null, this means that it is a human user's turn to play. In this case, play() calls ui.getUserInput(), employing the user interface to input a value from the keyboard. The user's input must also be converted from String to int. Once the value of sticks is set, either from the user or from the IPlayer, the play() method calls takeSticks(). If the move is legal, then it changes whose turn it is, and the loop repeats.
[Page 386]
There are a couple of important points about the design of the play() method. First, the play() method has to know what to do with the input it receives from the user or the IPlayer. This is game-dependent knowledge. The user is inputting the number of sticks to take in OneRowNim. For a tic-tac-toe game, the "move" might represent a square on the tic-tac-toe board. This suggests that play() is a method that should be implemented in OneRowNim, as it is here, because OneRowNim encapsulates the knowledge of how to play the One-Row Nim game.
Encapsulation of game-dependent knowledge
[Page -
JPA Arhitectural Design Decision
Hi,
I'm building a 1 tier web shop, using mostly Ajax, Servlets and JPA and I need your advice on a design decision.
When a user demands to see the products belonging to a particular category of products, my DAO object returns to the servlet a java.util.List<Product>, where Product is a JPA entity. In the servlet class I "manually" create the Ajax XML response, the user gets to see the products, everything is nice and great.
I am not happy with the fact that the list of products remains detached in the servlet class, sort of say, and when another user demands to see the same products another list gets greated. These are objects that have method scope, but still they are on the stack, right? For 100 users who want to see 100 products each, the no. of objects created could cause the application to have a slower reponse time.
So my question is about the design of the application.
I obtain the list of products in the servlet class and construct the XML response. Right before sending the response, should I pass the list of products back to the DAO, and ask the EntityManager to merge the products? Will this reduce the no. of objects my application creates? Shouldn't I do this because I'm merging entities that have not been changed and the merge operation is time consuming?
Should I not pass back the products to the DAO and set each product in the list to reference null and call System.gc() ?
Keeping in mind, that my main concern is application response time, not reduced development time, are there any other suggestions you can make?first of all, a merge is only used to synchronize a changed entity that is not managed by an entity manager with the database. Why did you even come to the conclusion that you might need this?
No you don't nullify the entities in the list. You let the entire list go when you are done with it. Manually nullifying can hinder the garbage collector, just don't do it unless you have a very good reason for doing so.
Your main problem seems to be that you don't like the fact that you are fetching 100 objects for both users, putting duplicate objects in memory on the server. Are you sure this is a problem? You shouldn't be thinking about optimizations while you are still developing you know. I would wait until you are done, then profile the application to see where bottlenecks are; if fetching those 100 products turns out to take a lot of system resources, THEN optimize it.
You may want to look into caching. If for example under water you use Hibernate as the persistence provider, search for "hibernate cache" using google. -
HELP !!!!!! Design decision...!!!!!
Hello,
I am in a dilemma of making a design decision . We are developing a business tier component. This is going to talk to webservices on the backend. Right now it is going to integrate with 2 different backend systems through web services. In future it might support more of such backend systems.
And there are clients (web app, xml app) who interface with the component.
Most of the data elements passed over to backend systems is similar for both the systems, but some are different.
Now is it a good design to make 2 different client interfaces for 2 backend systems ? so that ,clients upfront decide which interface to use. This is more cleaner and easier implementation.
Or is it good to have a generic interface, and component then figures out which data to use and to which backend system to talk to.
Please help,
ThanksThere are several patterns that could apply, but the most widly used is probably the MVC (Model View Controller) pattern.
With the pattern the View layer is the front end (in your case this would be the web app / xml app).
The Controller would be your middle tier, this layer is responsible for relaying requests of the View layer to the Model layer.
The Model layer would be your backend webservices.
As said, the controler is responsible for relaying the requests from the view layer to the correct webservice. This means you need to have some way to know how to do this. You can employ several methods to do this.
You could have different methods for the different webservices, this is the most straight forward way.
Or you could look at the provided parameters and decide where you need to go based on that. This is slightly more difficult, but when you have two or more webservices that do almost the same thing, this might be the better way to go.
If you really wanted to make things fancy, you could employt the second method and have the checks be based on rules you configure through a dynamically loaded file, this way, you could (theoratically) build your middle tier in such a way that you can add new front ends / back ends without having to redo the middle tier. This might eventually be the cleanest / best way to go, but it is also the most difficult and takes a lot of planning beforehand.
Mark -
Abstract classes vs adapter classes
Hi,
If we need to make use of an adapter class, why do need the interface -- won't abstract classes serve the same purpose???
I mean if we are going to extend the adapter class and then override the method we want to implement -- why the need for the interface at all -- wouldn't it be simpler if we just used an abstract class and override the function we want to implement????
Thanx,
TheJavaKidEvery once in a while, you'll want to make a WindowListener (for example) that also extends another class. You couldn't do this if WindowListener weren't an interface.
-
Why are JDBC related classes Interfaces???
Why are the JDBC related classes java.sql.CallableStatement
java.sql.Connection
java.sql.PreparedStatement
java.sql.ResultSet
java.sql.Statement Interfaces??? Where are the implementations of these interfaces found??? What are the pros and cons involved in doing so???
thx in advance!!!Are these classes Interfaces from the very first release of Java specifications??? I'm quite doubtful
about this.You're also quite wrong.
They've been interfaces from the very beginning. If they hadn't been, there's no way JDBC drivers could plug & play as nicely as they do.
This is the beauty of all interfaces, by the way. It's a design worth emulating in your own work.
If not, in what release have they been made into Interfaces???Why are you so concerned? -
I can't understand the adapter class.
Can anyone plz explain that clearly???Source: http://www.dofactory.com/Patterns/PatternAdapter.aspx
Convert the interface of a class into another interface clients expect. Adapter lets classes work together that couldn't otherwise because of incompatible interfaces.
So if I have an interface Person and an interface Animal, then AnimalToPersonAdapter would take an Animal instance (probably in its constructor) and fulfill the contract of the Person interface. It 'bridges' the two interfaces. Sometimes the adapter is bi-directional (meaning it can convert from Animal to Person and back, fulfilling both interface contracts) or more commonly uni-directional, as above.
- Saish -
can someone please advise on what I should do? unable to uninstall the Itunes. It states "could not open key HKEY_LOCAL_MACHINE\SOFTWARE\CLASSES\INTERFACE\(915DA835-02FE-4953-92FA-624BDF5D 85AB) VEIFY THAT YOU HAVE SUFFICIENT ACCESS TO THAT KEY, OR CONTACT YOUR SUPPORT PERSONNEL, Which i did . I contacted the apple support and they could not help. has anyone gotten this error? Did some research some results show that this has occurred during updates on the itunes but has not seen how to successfully uninstall without getting this error. I attempted to use the control panel and uninstall but it provides me with the same error all the time. I NEED SOME Answers on this issue. Can you please help?!
Perhaps try the fixit from the following Microsoft web page. (Try the "problems uninstalling" option.)
Fix problems with programs that can't be installed or uninstalled -
Error while transporting class interface
hi,
i have developed class interfaces where i'm using a z-structure(eg ZBMTBATCH) for type definition in public section.
The interface is activated and is working fine is development server.
when i transported it in quality, the transport req failed showing error " ZBMTBATCH not found".
This structure is a trans table and is activated.
Same type of error occured in transport req of all other class interface . only difference is the structure.
The class interface throwing this error has one common similarity, the error it is throwing is for the first declaration.
i mean in public section if declaration is of type :
tbatch type ZBMTBATCH
than in transport log its throwing error as "ZBMTBATCH not found"
please suggest some reasonsHello,
Are u transporting the Structure also together with the Class.
If not first add the Structure to a TR and move it to Quality system. Then Re transport the TR with Classes.
Hope this will helps you.
Regards,
Vasanth -
I know what a class is; I know what an interface is. Today I was looking at somebodies code, and in SE24 they have defined a "Class Interface", NOT a class or an interface.
Does anybody know:
1) What is the difference between this and an ordinary interface?
2) How do you create it in SE24 (When you create a new entity here it gives the option for "Class" or "Interface", but not "Class Interface"?What you may be seeing is the description next to the actual class name in SE24, where it says "Class Interface". Is this right? If so, just know that this is a class and the description here is a little misleading. There are only classes and interfaces in regard to obect types, there is not a third.
http://help.sap.com/saphelp_erp2005/helpdata/en/ee/e440ac70a111d1b44c0000e8a52bed/frameset.htm
Regards,
Rich Heilman
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