Instantiation of a sub class

I have a basic question abt instantiating a class.
I have a base class 'beverage' and a child class 'tea' with a overridden method in child class 'price'.
I want to know the difference b/w the following instantiating statements:
- beverage b = new tea();
- tea t = new tea();
What exactly happens when compiler sees the first statement?? Is the object 'b' is of type 'tea'???
Please advice or send me any links which would help in understanding that concept.

What exactly happens when compiler sees the first
statement?? Is the object 'b' is of type 'tea'???No. The reference named b is of type Beverage. The object it points to is of type Tea. References are not objects, just pointers to them.

Similar Messages

Instantiation of similar object over a super class deciding the sub class

Hello all
First, sorry if I'm duplicating an already answered question. I didn't searched very deep.
Initial position:
I have 2 Object (A1 and A2) which share the most (about 90%) of their instance variables an the associated methods. The values of the instance variables are retrieved in the real implementation from a stream. Depending of the data of the stream, I have to instantiate either a A1 or A2 object.
A test implementation (using an int in case of the stream):
The super class A:
package aaa;
public class A
protected int version = -1;
protected String name = null;
protected AE ae = null;
protected A()
protected A(int v)
    // Pseudo code
    if (v > 7)
      return;
    if (v % 2 == 1)
      this.version = 1;
    else
      this.version = 2;
public final int getVersion()
    return this.version;
public final String getName()
    return this.name;
public final AE getAE()
    return this.ae;
}The first sub class A1:
package aaa;
public final class A1 extends A
protected A1(int v)
    this.version = v;
    this.name = "A" + v;
    this.ae = new AE(v);
}The second subclass A2:
package aaa;
import java.util.Date;
public final class A2 extends A
private long time = -1;
protected A2(int v)
    this.version = v;
    this.name = "A" + v;
    this.time = new Date().getTime();
    this.ae = new AE(v);
public final long getTime()
    return this.time;
}Another class AE:
package aaa;
public class AE
protected int type = -1;
protected AE(int v)
    // Pseudo code
    if (v % 2 == 1)
      this.type = 0;
    else
      this.type = 3;
public final int getType()
    return this.type;
}To get a specific object, I use this class:
package aaa;
public final class AFactory
public AFactory()
public final Object createA(int p)
    A a = new A(p);
    int v = a.getVersion();
    switch (v)
    case 1:
      return new A1(v);
    case 2:
      return new A2(v);
    default:
      return null;
}And at least, a class using this objects:
import aaa.*;
public final class R
public static void main(String[] args)
    AFactory f = new AFactory();
    Object o = null;
    for (int i = 0; i < 10; i++)
      System.out.println("===== Current Number is " + i + " =====");
      o = f.createA(i);
      if (o instanceof aaa.A)
        A a = (A) o;
        System.out.println("Class   : " + a.getClass().getName());
        System.out.println("Version : " + a.getVersion());
        System.out.println("Name    : " + a.getName());
        System.out.println("AE-Type : " + a.getAE().getType());
      if (o instanceof aaa.A2)
        A2 a = (A2) o;
        System.out.println("Time    : " + a.getTime());
      System.out.println();
Questions:
What would be a better way to encapsulate the logic into their respective objects ? Is there a way to let the super class A itself identify the type of the object and then extend from A to either A1 or A2 ?
Thanks in advance
Andreas

Hello jduprez
First, I would thank you very much for taking the time reviewing my problem.
Just for the record: have you considered regular serialization? If you control the software at both ends of the stream, you could rely on standard serialization mechanism to marshall the objects and unmarshall them automatically.In my case, I can't control the other site of the stream. At the end, the data comes from a FileInputStream and there aren't objects on the other site, only pur binary data.
- It seems you have one such factory class. Then you already have encapsulated the "determine class" logic, you don't need to add such logic in superclass A.I thought from an OO view, that the super class A is responsible of doing that, but that's where the problem starts. So at the end, it's better doing it in the factory class.
- A itself encapsulates the logic to load its own values from the stream.
- A1 and A2 can encapsulate the logic to load their own specific value from a stream (after the superclass' code has loaded the superclass' attributes values).
My advise would be along the lines of:
public class A {
.... // member variables
public void load(InputStream is) {
... // assign values to A's member variables
// from what is read from the stream.
public class A1 extends A {
... // A1-specific member variables
public void load(InputStream is) {
super.load(is);
// now read A1-specific values
public class AFactory {
public A createA(InputStream is) {
A instance;
switch (is.readFirstByte()) {
case A1_ID:
a = new A1();
break;
case A2_ID:
a = new A2();
break;
a.load(is);
}The example above assumes you have control over the layout of the data in the stream (here for a given A instance, the attributes defined in A are read first, then come the subclass-specific attributes.
The outcome is: you don't have to create a new A( ) to later create another instance, of a subclass.I like the idea. In the AFactory, is the "A instance;" read as "A a;" ?
Is there a way to let the super class A itself identify the type of the object and then extend from A to either A1 or A2 ?Note I initially read this question as "can an instance of a class mutate into another class", to which the answer is no (an object has one single, immutable class; it is an instance of this class, and of any superclass and superinterface, but won't change its class at runtime).Yes, I have been thinking about a way for mutating into a subclass to keep the already initialized values from the A class without copying or parsing again. But preventing an instance of an A class will be my way. So, in this aspect, Java didn't changed in the last 10 years... It's a long time ago I've used Java for some real projects.
You can, however, create an instance of another class, that copies the values off a priori A instance. Your example code was one way, another way could be to have a "copy constructor":
public class A {
public A(A model) {
this.att1 = model.att1;
this.att2 = model.att2;
public class A1 {
public A1(A model) {
super(model);
... // do whatever A1-specific business
)Still, I prefer my former solution less disturbing: I find the temporary A instance redundant and awkward.Nice to know. I prefer the first solution too.
Thank you again for the help and advices. My mind is searching sometimes for strange solutions, where the real is so close ;-)
Andreas

Sub-class objects changing lovu2019s in XI 3.0

Hello all,
I have a XI 3.0 universe where I have several classes and sub-classes like this;
Class1
....Subclass1
.............Object 1
.............Object 2
.............Object 3
....Subclass2
.............Object 4
.............Object 5
.............Object 6
...Subclass3
.............Object 7
.............Object 8
.............Object 9
Class2
....Subclass1b
.............Object 10
.............Object 11
.............Object 12
While updating the objects lovu2019s (for sorting) in the properties window, Iu2019ve noticed that beginning with Object 4 that the lovu2019s are changing back to that of Object 1, this is also the case for Object 5 (changes to Object 2u2019s lov) all the way through Object 12. It seems that no mater how often I set and apply the sorted lov for all objects, they take on the settings of the objects in the first sub-class in my universe. When querys are ran from WebIntelligence, they display the correct SQL (and return no results as there is no data in my dev database as yet). Objects in other classes (not sub-classes) seem to be fine. Has anyone seen this type of behavior before?
Iu2019m thinking that I will need to go to 3.1 and suspect this may be a bug, any thoughts or comments are appreciated....

Hi Didier,
I did copy some some of the objects from a subclass to another, and to make sure this was not the issue, I re-created new ones and had the same issue. I was not aware that previous BOE versions (LOVs) had the issue though, which makes some sense.
At the moment, I'm suspecting this is a bug so I am asking the client to upgrade to 3.1 to see if the issue persist (I suspect it may), if so I will then open up a tech support case.
Thanks, Joe Szabo

Is it possible to OVERLOAD a super-class method in a sub-class?

Hi all,
I have a query that
Is it possible to OVERLOAD a super-class method in a sub-class?
If it is possible, please give me an example.
Thanks,
Hari

Hi,
Is the method int Display(int a){} overloading
the super-class's void Display() method? If
possible, please clarify this and how it would be
method overloading?
hanks,
Hari
Hi Hari,
Yes, it is possible. Look at this piece of code:
class Senior
     void Display()
          System.out.println("Super class method");
class Junior extends Senior
     int Display(int a)
          System.out.println("Subclass method: "+a);
          return(a+10);
     }> }
class example
     public static void main(String args[])
          Junior j = new Junior();
          j.Display();
System.out.println("Subclass method
od "+j.Display(5));
Is this what you were asking? Hope this helped.Hi,
I guess you guys are confused here...
Overloading is achieved by methods in the same class...
Overriding is across a superclass subclass methds.

Java Sub-Classing Error. Please Help!

I am trying to understanding some classing sub-classing and the convertion exercise. The errors appear with the code at the bottom at compilation.
HelloWorld.java:7: cannot resolve symbol
symbol : method uniqueInSubSayHello()
location: class SayHello
sh2.uniqueInSubSayHello();
^
HelloWorld.java:11: cannot resolve symbol
symbol : method uniqueInSubSayHello()
location: class SayHello
sh2.uniqueInSubSayHello();
^
class HelloWorld {
     public static void main (String args[]) {
          subSayHello subsh=new subSayHello();
          SayHello sh2=subsh;
          sh2.haha();
          sh2.uniqueInSubSayHello();
     int callUnique() {
          sh2.uniqueInSubSayHello();
class SayHello {
     public SayHello() {
     public void haha() {
class subSayHello extends SayHello {
     public subSayHello() {
     void uniqueInSubSayHello() {

On line 7, sh2 points to an object of type SayHello (as you assigned two lines earlier) and therefore does not know about method UniqueUnSubSayHello.
On line 11, sh2 has not been declared, since sh2 is not a variable declared globally within class SayHello. Therefore, it is not found.
Best regards,
Cemil

Exception in super and sub class

when super class method throws an exception then sub class overridden method can throws child exception but when we talk about constructor why we throws parent class exception in derived class constructor????

tcbhardwaj wrote:
C() throws Throwable // why here parent of Exception class
void ok() throws ArithmeticException // why here child of RunTimeException classFirst, you never need to declare a throws clause for unchecked exceptions--RuntimeException, Error, and their descendants.
However, there are a couple of general rules for checked exceptions (such as IOException, SQLException, etc.). As you're studying these, keep in mind that a throws clause is a contract that promises what the method will not do. In particular, it doesn't promise that the method will throw those exceptions. It promises that it will not throw any other checked exceptions not covered by that throws clause.
1. A child method that overrides a parent method cannot throw any checked exception outside what's covered by the parent's throws clause. So if the parent method declared throws IOException, the child cannot declare throws Exception, or throws SQLException, because both of those are outside the IOException "sub-hierarchy."
2. A child method that overrides a parent method can declare to throw less than the parent throws. This is because, if the parent promises not to throw outside of some set, and the child promises not throw outside of a subset of that set, then clearly he's also not throwing outside of the parent's set. If the parent method declares throws SQLException, IOException, then the child can declare no exceptions at all, or just SQLException, or just IOException, or any combination of any of the subclasses of SQLE and IOE.
Rules 1 and 2 do not apply in the case of constructors, because no constructor can ever override another constructor.
3. When any method or constructor, A, invokes any other method or constructor, B, then any checked exception declared to be thrown by B must be either caught or declared to be thrown by A. If A catches or throws a parent of an exception thrown by B, then he's also implicitly catching or throwing the one that B mentions.

Do sub classes get their own copy of base class static members?

Hi,
I am sub classing a certain classwhich has a static member boolean used for status updating. I have two sub classes, each needing its own static copy of the boolean. Do they get their own copy, or must I redeclare the member in each sub class?
AC

You must re-declare them (hiding the superclass member) if you wish the subclass members to be "independent".
class Coin {
    public static int FOO;
    public static int BAR;
class Coin2 extends Coin {
    public static int BAR = 2;
    public static void main(String[] args) {
        FOO = 1;
        System.out.println("Coin FOO = " + Coin.FOO); // 1
        System.out.println("Coin2 FOO = " + Coin2.FOO); // 1
        System.out.println("Coin BAR = " + Coin.BAR); // 0
        System.out.println("Coin2 BAR = " + Coin2.BAR); // 2
}HTH! :o)

Servicegen include sub class used by serviceClass

I have AbstractWSBE class which will expose service to users, how can I include
all other classs used by the AbstractWSBE webservice class using servicegen?
should I use comma to list all other sub class with AbstractWSBE?
<servicegen
destEar="${ear_file}"
warName="${war_file}">
<service
javaClassComponents="com.netsboss.WSBE.inf.AbstractWSBE"
targetNamespace="${namespace}"
serviceName="WSBE"
serviceURI="/WSBE"
generateTypes="True"
expandMethods="True" >
</service>
</servicegen>

The javaClassComponent specified in the servicegen cannot be
abstract. At deploy time WS runtime need to create an instance
of this class.
http://manojc.com
"Stephen Zeng" <[email protected]> wrote in message
news:3edebe0a$[email protected]..
>
I have AbstractWSBE class which will expose service to users, how can Iinclude
all other classs used by the AbstractWSBE webservice class usingservicegen?
>
should I use comma to list all other sub class with AbstractWSBE?
<servicegen
destEar="${ear_file}"
warName="${war_file}">
<service
javaClassComponents="com.netsboss.WSBE.inf.AbstractWSBE"
targetNamespace="${namespace}"
serviceName="WSBE"
serviceURI="/WSBE"
generateTypes="True"
expandMethods="True" >
</service>
</servicegen>

Servicegen for sub-class inside vector variable of Super

java.lang.NoSuchMethodError
at com.netsboss.WSBE.model.QueryItemCodec.typedInvokeGetter(QueryItemCod
ec.java:87)
at com.netsboss.WSBE.model.QueryItemCodec.invokeGetter(QueryItemCodec.ja
va:56)
at weblogic.xml.schema.binding.BeanCodecBase.gatherContents(BeanCodecBas
e.java:295)
at weblogic.xml.schema.binding.CodecBase.serializeFill(CodecBase.java:25
3)
at weblogic.xml.schema.binding.CodecBase.serialize(CodecBase.java:195)
at weblogic.xml.schema.binding.RuntimeUtils.invoke_serializer(RuntimeUti
ls.java:184)loop
at weblogic.xml.schema.binding.RuntimeUtils.invoke_serializer(RuntimeUti
ls.java:170)
QueryItem {
private Vector airItiners;
public Vector getAirItiners() {
return airItiners;
public class AirItinerary implements Serializable{}
QueryItem is my return class. The return result will include sub class AirItinerary
in QueryItem's Vector. I notice servicegen will only generate stub and web.xml
for QueryItem.
I get above error, when the result return to client. How to generate necessary
sub-class inside a vector variable of Super class?
Stephen

Hi Stephen,
write my own ser/deser? Any other quick way?Our excellent support group ([email protected]) may be able to help with
an alternative solution. If you could create a small reproducer, then
this will help them with a clear picture of your goal.
One more problem, wls deloy my WSBE.ear as a war correctly. But error show noDouble check the console log for any messages. Also try:
http://[host]:[port]/[contextURI]/[serviceURI]
See: http://edocs.bea.com/wls/docs70/webserv/client.html#1051033 and
also check the console to verify the app is or is not deployed. See:
http://edocs.bea.com/wls/docs70/programming/deploying.html
HTHs,
Bruce
Stephen Zeng wrote:
>
Hi Bruce:
Our company use wsl7.0. We are not able to update to wls8 in this project. Do
I have to
write my own ser/deser? Any other quick way?
sub class variable:
public class AirItinerary implements Serializable{
private String air;
private Vector flightItem; //sub class of AirItineray
One more problem, wls deloy my WSBE.ear as a war correctly. But error show no
deloyment found. web-services.xml has been generated by servicegen under web-inf
path. Thanks Bruce.
Stephen
Bruce Stephens <[email protected]> wrote:
Hi Stephen,
The java.util.vector should be converted to a SOAP Array, see:
http://edocs.bea.com/wls/docs81/webserv/assemble.html#1060696 however
the issue of the sub-class is most likely the problem. Can you simplify
the data types? You may just have to write your own ser/deser, see:
http://edocs.bea.com/wls/docs81/webserv/customdata.html#1060764
This is with WLS 8.1, right?
Thanks,
Bruce
Stephen Zeng wrote:
java.lang.NoSuchMethodError
at com.netsboss.WSBE.model.QueryItemCodec.typedInvokeGetter(QueryItemCod
ec.java:87)
at com.netsboss.WSBE.model.QueryItemCodec.invokeGetter(QueryItemCodec.ja
va:56)
at weblogic.xml.schema.binding.BeanCodecBase.gatherContents(BeanCodecBas
e.java:295)
at weblogic.xml.schema.binding.CodecBase.serializeFill(CodecBase.java:25
3)
at weblogic.xml.schema.binding.CodecBase.serialize(CodecBase.java:195)
at weblogic.xml.schema.binding.RuntimeUtils.invoke_serializer(RuntimeUti
ls.java:184)loop
at weblogic.xml.schema.binding.RuntimeUtils.invoke_serializer(RuntimeUti
ls.java:170)
QueryItem {
private Vector airItiners;
public Vector getAirItiners() {
return airItiners;
public class AirItinerary implements Serializable{}
QueryItem is my return class. The return result will include sub classAirItinerary
in QueryItem's Vector. I notice servicegen will only generate stuband web.xml
for QueryItem.
I get above error, when the result return to client. How to generatenecessary
sub-class inside a vector variable of Super class?
Stephen

Can we chagne Super class method parameters in Sub class

Hi,
I created a super class. In that class i created a method. That method is having 4 input parameters and 4 export parameters.
I created a sub class for that super class. I need to use only 2 input parameters in this class rather than 4 parameters. I want to delete 2 Input parameters in the sub class of the super class method. Is it possible.
If possible. can we give an simple code or pseudo code?
regards,
krishna

Hi,
I think you can not.
Because, only public attributes can be inherited and they will remain public in the subclass.
for further detail check,
http://help.sap.com/saphelp_nw70/helpdata/en/1d/df5f57127111d3b9390000e8353423/content.htm
regards,
Anirban

Calling sub class method from superclass constructure

hi all
i have seen a program in which a super class constructure class methods of sub class before initialization of fields in subclass ,i want how this is posibble ?
thanks in advance

Hear is the code n other thing i have used final variable without initialization n compiler dosen't report error
abstract class Test
public Test()
System.out.println("In DemoClass Constructer");
this.show();
public void show()
System.out.println("In DemoClass Show() method");
class Sub1 extends Test
private final float number;
public Sub1(float n)
this.number=n;
System.out.println((new StringBuilder()).append("Number is==").append(number).toString());
int j;
public void show()
System.out.println("In Sub1 Class Show method ");
public class DemoClass
public static void main(String s[])
Sub1 obj1=new Sub1(5);
Sub1 obj2=new Sub1(6);
thanks for reply

Why are protected fields not-accessible from sub-classed inner class?

I ran across a situation at work where we have to sub-class an inner class from a third-party package. So, it looks something like this...
package SomePackage;
public class Outer {
   protected int x;
   public class Inner {
package OtherPackage;
public class NewOuter extends Outer {
   public class NewInner extends Outer.Inner {
}Now the NewInner class needs to access protected variables in the Outer class, just like the Inner class does. But because NewOut/NewInner are in a different package I get the following error message.
Variable x in class SomePackage.Outer not accessible from inner class NewOuter. NewInner.You can still access those protected variables from the NewOuter class though. So, I can write accessor methods in NewOuter for NewInner to use, but I am wondering why this is. I know that if NewOuter/NewInner are in the same package as Outer/Inner then everything works fine, but does not when they are in different packages.
I have to use JDK1.1.8 for the project so I don't know if there would be a difference in JDK1.2+, but I would think that nothing has changed. Anyway, if you know why Java disallows access as I have detailed please let me know.

Although I don't have the 1.1.8 JDK installed on my system, I was able to compile the following code with the 1.3.1_01 JDK and run it within a Java 1.1.4 environment (the JVM in the MSIE 5.5 browser). As long as you don't access any of the APIs that were introduced with 1.2+ or later, the classes generated by the JDK 1.2+ javac are compatible with the 1.1.4+ JVM.
//// D:\testing\SomePackage\Outer.java ////package SomePackage ;
public class Outer {
    protected int x ;
    public Outer(int xx) {
        x = xx ;
    public class Inner {
}//// D:\testing\OtherPackage\NewOuter.java ////package OtherPackage;
import SomePackage.* ;
public class NewOuter extends Outer {
    public NewOuter(int xx) {
        super(xx) ;
    public class NewInner extends Outer.Inner {
        public int getIt() {
            return x ;
}//// D:\testings\Test.java ////import OtherPackage.* ;
import java.awt.* ;
import java.applet.* ;
public class Test extends Applet {
    public void init () {
        initComponents ();
    private void initComponents() {
        add(new Label("x = ")) ;
        int myx = new NewOuter(3288).new NewInner().getIt() ;
        TextField xfld = new TextField() ;
        xfld.setEditable(false) ;
        xfld.setText(Integer.toString(myx)) ;
        add(xfld) ;
}//// d:\testing\build.cmd ////set classpath=.;D:\testing
cd \testing\SomePackage
javac Outer.java
cd ..\OtherPackage
javac NewOuter.java
cd ..
javac Test.java//// d:\testing\Test.html ////<HTML><HEAD></HEAD><BODY>
<APPLET CODE="Test.class" CODEBASE="." WIDTH=200 HEIGHT=100></APPLET>
</BODY></HTML>

Sub Class in applet

I have written an applet that does a mathematical operation on numbers then shows a diagram on the clicking of a button.
On the clicking of the button I removed the previous two panels and repainted the GUI with the diagram, created using a sub class/ The class header and constuctor is shown below for the sub class.
In netbeans, using applet viewer this works.
Yet for some reason when the applet code is used in a web page the main applet comes up fine and is operational but when clicking the diagram button nothing happens.
II would appreciate any help going?
Thanks
public class VennChart extends JPanel
      /**provides a venn diagram of fucntion
       *@param g is graphics component
      public void paintComponent(Graphics g)
         //frame initialisation
         super.paintComponent(g);
         //code to draw diagram
if(ae.getSource()==graph)
            pane.remove(holder);
            pane.remove(status);
            pane.repaint();
            pane.add(exit, "North");
            VennChart chart = new VennChart();
            temp = chart; //temporary JPanel variable to hold diagram
            pane.add(temp, "Center");
            pane.validate();
}

What error message do you get in the java console?

How do i Index on a Sub class

Hi,
Please let me know if there is a way to index on the vairable in a sub class.
Thanks & regards,
Ebe

Hi Cameron,
The design of the Object is as follows.
Object
--- getSubObjectList() - Returns SubObjectList
----- Contains the list of SubObject
---- SubObject Contains attributes which i query upon.
Please let me know a way how to index on these attributs. Please find the code am using below
Below is the extract method of my Extractor Class
public final class ObjectGraphNavigationValueExtractor extends
AbstractExtractor implements ValueExtractor, ExternalizableLite
public Object extract(Object object) {
if(this.path.equals("attr1") || this.path.equals("attr2")){
MyObject obj =
(MyObject)object;
SubObjectList subList = (SubObjectList) obj.getSubObjectList();
Object aoExtracted[] = subList.toArray();
for(int i=0;i<aoExtracted.length;i++){
SubObject objSubObject =
(SubObject) aoExtracted;
return new BeanWrapperImpl(SubObject).getPropertyValue(this.path);
return new BeanWrapperImpl(object).getPropertyValue(this.path);
I have applied index as follows.
cache.addIndex(new ObjectGraphNavigationValueExtractor("attr1"),true,null);
cache.addIndex(new ObjectGraphNavigationValueExtractor("attr2"),true,null);
Regards,
Ebe

Can we change the Super class attribute scope in Sub class

Hi.
I created a super class. In that i have 4 attributes. That attributes are PUBLIC.
I created a sub class. In that i got all super class attributes. I want to change that attributes as a Private. Is it possible.
If it is possible.Give me an Example with code or Pseudo code.
Regards.
Krishna.

Hi Krishna,
It is not possible... If you declare the Attributes again in Subclass of the same name as that of Super class
then the way of accessing them would be different from that of attributes in the main class.
Hope this would help you
Good luck
Narin

Instantiation of a sub class

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