Abstract Method in a Class with implemented method

I have a class which already has methods Implemented.I mean thse metgods are not abstract.I want only one method to be abstarct which will be overrideen by its subclass or derived Class
I have never tried this
Does anyone knows how to do this
If yes could you give me syntax of the method
Thanks in advance
CSJakharia

javax.swing.JComponent is an example of an abstract
class with no abstract methods. That is why the
following works:
JComponent component = new JComponent(){};
Not to forget you cannot instantiate abstarct classes
public abstract class Test
public String getName()
return "Mike";
public static void main(String[] args)
Test tt = new Test();
System.out.println(tt.getName());
}and you would get the error
The type Test cannot be instantiated.
You remove the abstract keyword and it would compile
good.No I am not misinterpreting I know what he is saying but I am closing the door of misinterpretation which I felt was possible. ;)
cheers

Similar Messages

In which case we need a class with all methods defined as abstract ?

In which case we need : A class with all methods defined as abstract (or should we go for Interface always in this case)

The concept of interface and abstract class overlaps sometime, but we can have the following thumb rule to use them for our specific need:
1) Interface: This should be use for code structuring. They standardize your application by providing a specific contract within and outside. If you think abstract class also provide structure, then reconsider as it limits the structure re-usability when there are many super-classes to inherit from. Java allow multiple inheritance by interface and not by Abstract class.
2) Abstract Class: This should be use for code-reusability. Interface doesn't have any code so can't be used for code-reusability.
Actually we can use both to provide the best.Taking a refernce to J2EE framework, the "Servlet" is an interface. It laids down the contract/structure for any code to be a servlet.
But the "GenericServlet" class is an abstract class which provides implementation of some of the methods defined in the "Servlet" interface and leave some method abstract.
Thus we see that the "Servlet" interface standardise the structure and the "GenericServlet" abstract class gives code re-usability.
Original Question:
In which case we need a class with all methods defined as abstract ?To this question, as all methods are abstarct we don't have option for code-reusability. so why not add standard structure concept to your application. So if there is not any restriction on making the field variable(if any) as final, we should go with the interface concept.

Testing ActionScript classes with native methods?

Hi,
I have an ActionScript class that I'm writing and would like to test using FlexUnit.
The only issue is that the ActionScript class has a member in it that is a class with native methods.
So, I get the following error when trying to run a test of that ActionScript class:
VerifyError: Error #1079: Native methods are not allowed in loaded code.
Does anyone know of a way to get around this? FlexUnit seems not to like native methods being present.
Thanks,
Matt

Hi casdvm,
by definition, you only own objects that you created using one of the alloc* methods, copy: or new:. All other objects (IIRC with a few noted exceptions) are autoreleased.
If you create convenience methods in your own class, you should follow the same rule. For example, if you have a class Pet and want to implement the method +petWithName, your code might look something like that:
+ petWithName: (NSString *)name
return [[[Pet alloc] initWithName: name] autorelease];
Alex

Enhanced SAP class with new methods - Not showing these from standard task

Dear Gurus,
I have enhanced SAP standard class with new methods. After I have activated my new methods and would like to create a workflow task using these new methods. when I create a task and input object category as "ABAP Class" and object type is SAP enhanced class. When I try to drop down for methods SAP is not showing my new methods. I do not know why. Am I missing any? Any help would be appreciated.
Note: Remember I am trying to use SAP ABAP class custom methods.
Thanks,
GSM

Hi,
Your thread has had no response since it's creation over
2 weeks ago, therefore, I recommend that you either:
- Rephrase the question.
- Provide additional Information to prompt a response.
- Close the thread if the answer is already known.
Thank you for your compliance in this regard.
Kind regards,
Siobhan

ECATT: How to access a protected method of a class with eCATT?

Hi,
These is a class with a protected method. now i am willing to automate the scenario with eCATT. Since the method is Protected i am unable to use createobj and use callmethod. Could anyone suggest me a work around for this ?
Regards
Amit
Edited by: Amit Kumar on Jan 10, 2012 9:53 AM

Hello Anil,
You can write ABAP Code to do that inside eCATT Command.
ABAP.
ENDABAP.
Limitation of doing that is you can only use local variable inside ABAP.... ENDABAP. bracket.
Regards,
Bhavesh

Question about methods in a class that implements Runnable

I have a class that contains methods that are called by other classes. I wanted it to run in its own thread (to free up the SWT GUI thread because it appeared to be blocking the GUI thread). So, I had it implement Runnable, made a run method that just waits for the thread to be stopped:
while (StopTheThread == false)
try
Thread.sleep(10);
catch (InterruptedException e)
//System.out.println("here");
(the thread is started in the class constructor)
I assumed that the other methods in this class would be running in the thread and would thus not block when called, but it appears the SWT GUI thread is still blocked. Is my assumption wrong?

powerdroid wrote:
Oh, excellent. Thank you for this explanation. So, if the run method calls any other method in the class, those are run in the new thread, but any time a method is called from another class, it runs on the calling class' thread. Correct?Yes.
This will work fine, in that I can have the run method do all the necessary calling of the other methods, but how can I get return values back to the original (to know the results of the process run in the new thread)?Easy: use higher-level classes than thread. Specifically those found in java.util.concurrent:
public class MyCallable implements Callable<Foo> {
public Foo call() {
return SomeClass.doExpensiveCalculation();
ExecutorService executor = Executors.newFixedThreadPool();
Future<Foo> future = executor.submit(new MyCallable());
// do some other stuff
Foo result = future.get(); // get will wait until MyCallable is finished or return the value immediately when it is already done.

Help with Declaring a Class with a Method and Instantiating an Object

hello all i am having trouble understanding and completing a lab tutorial again!
im supposed to compile an run this code then save work to understand how to declare aclass with a method an instantiate an object of the class with the following code
// Program 1: GradeBook.java
// Class declaration with one method.
public class GradeBook
// display a welcome message to the GradeBook user
public void displayMessage()
System.out.println( "Welcome to the Grade Book!" );
} // end method displayMessage
} // end class GradeBook
// Program 2: GradeBookTest4.java
// Create a GradeBook object and call its displayMessage method.
public class GradeBookTest
// main method begins program execution
public static void main( String args[] )
// create a GradeBook object and assign it to myGradeBook
GradeBook myGradeBook = new GradeBook();
// call myGradeBook's displayMessage method
myGradeBook.displayMessage();
} // end main
} // end class GradeBookTest4
i saved above code as shown to working directory filename GradeBookTest4.java
C:\Program Files\Java\jdk1.6.0_11\bin but recieved error message
C:\Program Files\Java\jdk1.6.0_11\bin>javac GradeBook4a.java GradeBookTest4.java
GradeBookTest4.java:2: class, interface, or enum expected
^
GradeBookTest4.java:27: reached end of file while parsing
^
2 errors
can someone tell me where the errors are because for class or interface expected message i found a solution which says 'class? or 'interface' expected is because there is a missing { somewhere much earlier in the code. i dont know what "java:51: reached end of file while parsing " means or what to do to fix ,any ideas a re appreciated

Doesn't solve your problem, but this works for me...
public class GradeBook
public void displayMessage() {
    System.out.println( "Welcome to the Grade Book!" );
public static void main( String args[] ) {
    try {
      GradeBook gradeBook = new GradeBook();
      gradeBook.displayMessage();
    } catch (Exception e) {
      e.printStackTrace();
}

What's the differences between a singleton and a class with static methods

Hi everybody.
My question is in the subject. Perhaps "differences" is not the good word. The positive and negative points ?
Imagine you have to write a connection pool, sure you gonna choose a singleton but why ?
Thank you very much.

A class is a class. Java doesn't have (and I wish it
did) a static outer class. Any class can extend
another class or implement an interface.A Class object cannot extend or implement anything - it is not under programmer control in any way. You can create a class which implements interfaces, but calling static methods is completely unrelated. Interfaces only affect instance methods, not class ones. I think all of your comparison to C++ is actually confusing you more. In Java, there is a real class object at runtime, as opposed to C++.
YATArchivist makes a good point about being able to
serialize, altho I've not met that desire in practice.
Maybe a concrete example would help.
mattbunch makes another point that I don't understand.
A class can implement an interface whether it sticks
its data in statics or in a dobject, so I guess I
still don't get that one.See my comment above. Static methods are free from all contractual obligations.
I prefer instance singletons to singleton classes because they are more flexible to change. For instance I created a thread pool singleton which worked by passing the instance around, but later I needed two thread pools so I made a slight modification to the class and poof! no more singleton and 99% of my code compiled cleanly against it.
When possible, I prefer to hand the instance off from object to object rather than have everything call Singleton.instance() since it makes changes like I mentioned earlier more feasible.

Creation of a static class with private methods

I'm new to java programming and am working on a project where I need to have a static class that does a postage calculation that must contain 2 private methods, one for first class and one for priority mail. I can't seem to figure out how to get the weight into the class to do the calculations or how to call the two private methods so that when one of my other classes calls on this class, it retrieves the correct postage. I've got all my other classes working correct and retrieving the information required. I need to use the weight from another class and return a "double". Help!!!
Here's my code:
* Title: Order Control 
* Description: Order Control Calculator using methods and classes
* Copyright: Copyright (c) 2002
* Company: Info 250, sec 001, T/TH 0930
* @author Peggy Blake
* @version 1.0, 10/29/02
import javax.swing.*;
public class ShippingCalculator
static double firstClass, priorityMail;
//how do I get my weight from another class into this method to use??? not sure I understand how it works.
public static double ShippingCalculator(double weight)
String responseFirstClass;
double quantity, shippingCost;
double totalFirstClass, firstClass, priorityMail, totalShipping;
double priorityMail1 = 3.50d;//prioritymail fee up to 1 pound
double priorityMail2 = 3.95d;//prioritymail fee up to 2 pounds
double priorityMail3 = 5.20d;//prioritymail fee up to 3 pounds
double priorityMail4 = 6.45d;//prioritymail fee up to 4 pounds
double priorityMail5 = 7.70d;//prioritymail fee up to 5 pounds
quantity = 0d;//ititialization of quantity
// weight = 0d;//initialization of weight
// shippingCost = 0d;
//calculation of the number of items ordered..each item weights .75 ounces
quantity = (weight/.75);
if (quantity <= 30d)
//add 1 ounce to quantities that weigh less than 30 ounces
weight = (weight + 1);
else
//add 2 ounces to quantities that weigh more than 30 ounces
weight = (weight + 2);
if (weight > 80d)
//message to orderclerk ..order over 5 lbs, cannot process
JOptionPane.showMessageDialog(null, "Order exceeded 5 lbs, cannot process");
//exit system, do not process anything else
System.exit (0);
else
if (weight < 14d)
//send message to customer: ship firstclass or priority, y or n
responseFirstClass = JOptionPane.showInputDialog(null, "Ship first class? y or n?");
if (responseFirstClass.equals("y"))
//compute FirstClass shipping cost
totalFirstClass = ((weight - 1) * .23d) + .34d;
firstClass = totalFirstClass;
else
//compute PriorityMail cost for orders less than 14 ounces
priorityMail = (priorityMail1);
else
if (weight <=16d)
//compute totalshipping for orders up to 16 ounces
priorityMail = (priorityMail1);
else
if (weight <=32d)
//compute totalshipping for orders up to 32 ounces
priorityMail = (priorityMail2);
else
if (weight <=48d)
//compute totalshipping for orders up to 48 ounces
priorityMail = (priorityMail3);
else
if (weight <= 64d)
//compute totalshipping for orders up to 64 ounces
priorityMail = (priorityMail4);
else
//compute totalshipping for orders up to 80 ounces
priorityMail = (priorityMail5);
priorityMail = 0d;
firstClass = 0d;
firstClassMail ();
priorityMailCost ();
//I think this is where I should be pulling the two methods below into my code, but can't figure out how to do it.
shippingCost = priorityMail + firstClass;
return (shippingCost);
}//end method calculate shipping
private static double firstClassMail()//method to get first class ship cost
return (firstClass);
}//end method firstclass shipping
private static double priorityMailCost()//method to get priority mail cost
return (priorityMail);
}//end method priorityMail
}//end class shipping calculator

public class A {
public String getXXX () {
public class B {
A a = new A();
public void init () {
a.getXXX();
}

Extending classes with private methods?

my understanding of extending classes is that you gain all the functions and methods of that class thus You could over ride any one of them. How ever I am confused on weather or not you inherit and can over ride private methods of the class you are extending or if you have to have all methods public in an extended class.
hope that makes sense, an example can bee seen bellow.
package
     public class Class1
          public function apples():void
               //some code
          private fnctuin bananas():void
               //more code
package
     public class Class2 extends Class 1
          override public function apples():void
               //i changed code
          //can I over ride bananas?

you can only override methods that would be inherited. a private method won't be inherited:
http://www.kirupa.com/forum/showthread.php?223798-ActionScript-3-Tip-of-the-Day/page5

Apply static method requirements on class (Static interface methods)?

I have a set of classes where is class is identified with a unique ID number. So each class has a public static int getId() method. Each class also has either a constructor that takes a byte array or a static factory method that takes a byte array.
I would like to maintain a hashmap of these classes keyed to the ID's however I am not sure how to have some interface of abstract parent class that requires each of these classes to implement these static methods.
What I was hoping to do was something like this>>>
 public interface MyClasses{
 static MyClasses createInstance(byte[] data);
 HashMap<Integer, MyClasses> map;
 public void init() {
 map = new HashMap<Integer, MyClasses>();
 map.put(Class1.getId(), Class1.class);
 map.put(Class2.getId(), Class2.class);
 public void createInstance (int id, byte[] data) {
 map.get(id).createInstance(data);
 }Is there some way I could do this?

What about something like this?
public interface Initializable
 public void initialize(byte[] data);
public class Factory
 private final Map<Integer, Initializable> map = new HashMap<Integer, Initializable>();
 public void registerClass(int id, Class klass)
 if (! Initializable.class.isAssignableFrom(klass))
 // you may also want to ensure the class declares a parameterless constructor
 throw new IllegalArgumentException("duff class");
 if (this.map.keySet().contains(id))
 throw new IllegalArgumentException("duff id");
 this.map.put(id, klass);
 public Initializable createInstance(int id, byte[] data)
 // need some exception handling of course
 Initializable i = map.get(id).newInstance();
 i.initialize(data);
 return i;
}

Access instance method of a class inside instance method of another class

Hi Friends
I have to use one c1->m1.
c1 is a public instantiation and m1 is a public Instance Method.
I called this m1 method by creating c1 object for class c1.
But problem is inise M1 method,i have a statement
CALL METHOD mo_central_person->if_hrbas_pd_object~read_infty.
here mo_central_person is of type some other class c2.
As without creating the object,i didn't use the above interface method.
Can please suggst me how to handle this.
Regards,
Sree

class a definition.
public section.
methods : display,
            disp.
data : a(10) type c value '10',
         b(5) type c value 'abc'.
endclass.
class a implementation.
method display.
    write : a.
endmethod.
method disp.
    write : b.
endmethod.
endclass.
class b definition inheriting from a.
public section.
methods : display1.
data : c(7) type c value '7'.
endclass.
class b implementation.
method display1.
   call method display( ).
    write c.
endmethod.
endclass.
start-of-selection.
data : o_obj type ref to b.
create object o_obj.
call method o_obj->display1.
the method display is in class a.
we can call this method in class b using the following statement.
method display1.
   call method display( ).
    write c.
endmethod.

Using a non-static vector in a generic class with static methods

I have a little problem with a class (the code is shown underneath). The problem is the Assign method. This method should return a clone (an exact copy) of the set given as an argument. When making a new instance of a GenericSet (with the Initialize method) within the Assign method, the variables of the original set and the clone have both a reference to the same vector, while there exists two instances of GenericSet. My question is how to refer the clone GenericSet's argument to a new vector instead of the existing vector of the original GenericSet. I hope you can help me. Thanks
package genericset;
import java.util.*;
public class GenericSet<E>{
private Vector v;
public GenericSet(Vector vec) {
v = vec;
private <T extends Comparable> Item<T> get(int index) {
return (Item<T>) v.get(index);
public static <T extends Comparable> GenericSet<T> initialize() {
return new GenericSet<T>(new Vector());
public Vector getVector() {
return v;
public static <T extends Comparable> GenericSet<T> insert (GenericSet<T> z, Item<T> i){
GenericSet<T> g = assign(z);
Vector v = g.getVector();
if (!member(g,i))
v.addElement(i);
return g;
public static <T extends Comparable> GenericSet<T> delete(GenericSet<T> z, Item<T> i){
GenericSet<T> g = assign(z);
Vector v = g.getVector();
if (member(g,i))
v.remove(i);
return g;
public static <T extends Comparable> boolean member(GenericSet<T> z, Item<T> i) {
Vector v = z.getVector();
return v.contains(i);
public static <T extends Comparable> boolean equal(GenericSet<T> z1, GenericSet<T> z2) {
Vector v1 = z1.getVector();
Vector v2 = z2.getVector();
if((v1 == null) && (v2 != null))
return false;
return v1.equals(v2);
public static <T extends Comparable> boolean empty(GenericSet<T> z) {
return (cardinality(z) == 0);
public static <T extends Comparable> GenericSet<T> union(GenericSet<T> z1, GenericSet<T> z2) {
GenericSet<T> g = assign(z1);
for(int i=0; i<cardinality(z2); i++) {
Item<T> elem = z2.get(i);
insert(g, elem);
return g;
public static <T extends Comparable> GenericSet<T> intersection(GenericSet<T> z1, GenericSet<T> z2) {
GenericSet<T> g = initialize();
for(int i=0; i<cardinality(z2); i++) {
Item<T> elem = z2.get(i);
if(member(z1, elem))
insert(g, elem);
return g;
public static <T extends Comparable> GenericSet<T> difference(GenericSet<T> z1, GenericSet<T> z2) {
GenericSet<T> g = initialize();
for(int i=0; i<cardinality(z1); i++) {
Item<T> elem = z1.get(i);
if(!member(z2, elem))
insert(g, elem);
for(int i=0; i<cardinality(z2); i++) {
Item<T> elem = z2.get(i);
if(!member(z1, elem))
insert(g, elem);
return g;
public static <T extends Comparable> GenericSet<T> assign(GenericSet<T> z) {
GenericSet<T> g = initialize();
for(int i=0; i<cardinality(z); i++) {
Item<T> elem = z.get(i);
insert(g, elem);
return g;
public static <T extends Comparable> boolean subset(GenericSet<T> z1, GenericSet<T> z2) {
for(int i=0; i<cardinality(z1); i++) {
Item<T> elem = z1.get(i);
if(!member(z2, elem))
return false;
return true;
public static <T extends Comparable> int cardinality(GenericSet<T> z){
Vector v = z.getVector();
return v.size();
}

The issue is not "reference a non-static interface", but simply that you cannot reference a non-static field in a static method - what value of the field ed would the static method use? Seems to me your findEditorData should look something like this: public static EditorBean findEditorData( String username, EditorBean editorData )
 return editorData.ed.findEditor( username );
 }

Singleton class with static method

Hi,
I have made a fairly simple singletion class STClass. EX:
Consider tow cases
CASE-1:
private static STClass singleInstance;
private static int i;
private STClass()
public static STClass instance()
     if (singleInstance == null)
          singleInstance = new STClass();
          loadConfigFile("XYZ");
     return singleInstance;
private static void loadConfigFile(String fileName)
     //SOME CODE in which use private variable "i"
CASE-2:
private static STClass singleInstance;
private int i;
private STClass()
     loadConfigFile("XYZ");
public static STClass instance()
     if (singleInstance == null)
          singleInstance = new STClass();
     return singleInstance;
private void loadConfigFile(String fileName)
     //SOME CODE in which use private variable "i"
What is the differnce between two case and which one will be best and why???
Someone told me "If u keep variables and methods as static the the whole purpose of singleton class is defeated"
please justify this statement

It seems to me that this way should be more "correct":
public class STClass {
private static STClass singleInstance;
private int i;
private STClass() {
public static STClass getInstance() {
if (singleInstance == null) {
singleInstance = new STClass();
singleInstance.loadConfigFile("XYZ");
return singleInstance;
private void loadConfigFile(String fileName) {
//SOME CODE in which use private variable "i"
}And it is also compatible with your CASE-2.
Hope this helped,
Regards.I wouldnot agree with this piece of code here because of JMM bug. check this
http://www.javaworld.com/jw-02-2001/jw-0209-double-p2.html
What about proposing your own version, explained ?...

How to call setter Method of ActionScript class with in a Flex Application

Hi
I have Action class as shown :
public class MyClass
private var name:String
public function get name():String {
    return _initialCount;
public function set name(name:String):void {
    name = name;
Now please let me know how can i access this Action class under my Flex Application and call the setter Method of it to set the value for the name .
For example on entering some data in a TextInput and click of a submit Button , on to the Event Listener , i want to call the set name method of my ActionScript class .
Please share your ideas on this .

Thanks Gordon for your resonse .
Say for example my Action class is like this :
public class MyClass
private var name:String
public function get name():String {
    return name;
public function set name(name:String):void {
    name = name;
This is inside the MXML
I know this way we can do it
public var myclass:MyClass = new MyClass();
myclass.name="Kiran";
Now my query is can we do in this way also ??
myclass.set name(SomeTextInput.text);
Please share your views on this , waiting for your replies .
Thanks in advance .

Abstract Method in a Class with implemented method

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