Access overriden method of an abstract class

class Abstract
abstract void abstractMethod(); //Abstract Method
void get()
System.out.print("Hello");
class Subclass extends Abstract
void abstractMethod()
System.out.print("Abstract Method implementation");
void get()
System.out.print("Hiiii");
In the above code, i have an abstract class called "Abstract", which has an abstract method named "abstractMethod()" and another method called "get()".
Now, this class is extended by "Subclass", it provides implementation for "abstractMethod()", and also overrides the "get()" method.
Now my problem is that i want to access the "get()" method of "Abstract" class. Since it is an abstract class, i cant create an object of it directly, and if i create an object like this:
Abstract obj = new Subclass();
then, obj.get() will call the get() method of Subclass, but how do i call the get() method of Abstract class.
Thanks in advance

hey thanks a lot,, i have another doubt regarding Abstract classes.
i was just trying something, in the process, i noticed that i created an abstract class which does not have any abstract method, it gave no compilation errors. was wondering how come this is possible, and what purpose does it solve?

Similar Messages

Calling a method from an abstract class in a seperate class

I am trying to call the getID() method from the Chat class in the getIDs() method in the Outputter class. I would usually instantiate with a normal class but I know you cant instantiate the method when using abstract classes. I've been going over and over my theory and have just become more confused??
Package Chatroom
public abstract class Chat
   private String id;
   public String getID()
      return id;
   protected void setId(String s)
      id = s;
   public abstract void sendMessageToUser(String msg);
Package Chatroom
public class Outputter
public String[] getIDs()
     // This is where I get confused. I know you can't instantiate the object like:
        Chat users=new Chat();
        users.getID();
I have the two classes in the package and you need to that to be able to use a class' methods in another class.
Please help me :(

I have just looked over my program and realised my class names are not the most discriptive, so I have renamed them to give you a clearer picture.
package Chatroom
public abstract class Chatter
private String id;
public String getID()
return id;
protected void setId(String s)
id = s;
I am trying to slowly build a chatroom on my own. The Chatter class is a class that will be used to represent a single logged in user and the user is given an ID when he logs in through the setId and getID() methods.
package Chatroom;
import java.util.Vector;
public class Broadcaster
private Vector<Chatter> chatters = new Vector<Chatter>();
public String[] getIDs()
// code here
The Broadcaster class will keep a list of all logged-in users keeps a list of all the chats representing logged-in users, which it stores in a Vector.I am trying to use the getIDs() method to return an array of Strings comprising the IDs of all logged-in users, which is why im trying to use the getID() method from the Chat class.
I apologise if I come across as clueless, it's just I have been going through books for about 4 hours now and I have just totally lossed all my bearings

Non-abstract methods in a Abstract class

Abstract Class can contain Non-abstract methods.
and Abstract Classes are not instantiable as well
So,
What is the purpose of Non-abstract methods in a Abstract class.
since we can't create objects and use it
so these non-abstract methods are only available to subclasses.
(if the subclass is not marked as abstract)
is that the advantage that has.(availability in subclass)
??

For example, the AbstractCollection class (in
java.util) provides an implementation for many of the
methods defined in the Collection interface.
Subclasses only have to implement a few more methods
to fulfill the Collection contract. Subclasses may
also choose to override the AbstractCollection
functionality if - for example - they know how to
provide an optimized implementation based on
characteristics of the actual subclass.Another example is the abstract class MouseAdapter that implements MouseListener, MouseWheelListener, MouseMotionListener, and that you can use instead of these interfaces when you want to react to one or two types of events only.
Quoting the javadocs: "If you implement the MouseListener, MouseMotionListener interface, you have to define all of the methods in it. This abstract class defines null methods for them all, so you can only have to define methods for events you care about."

Access DataControls methods in a java class

Hi All,
Jdeveloper Version 11.1.5
I have created DataControls for SessionFacade web service.
Inside the datacontrol there is a method getAllDepartments() which have a Return type which includes DaertmentId,DepartmentName,....
I want to know how can i access this method inside a Java Class and create a list of only departmentId.

You would need to add the method in the data control as a method action in your pageDef.
After that, you could access the method as mentioned above.
Thanks,
Navaneeth

How to access private method of an inner class using reflection.

Can somebody tell me that how can i access private method of an inner class using reflection.
There is a scenario like
class A
class B
private fun() {
now i want to use method fun() of an inner class inside third class i.e "class c".
Can i use reflection in someway to access this private method fun() in class c.

I suppose for unit tests, there could be cases when you need to access private methods that you don't want your real code to access.
Reflection with inner classes can be tricky. I tried getting the constructor, but it kept failing until I saw that even though the default constructor is a no-arg, for inner classes that aren't static, apparently the constructor for the inner class itself takes an instance of the outer class as a param.
So here's what it looks like:
        //list of inner classes, if any
        Class[] classlist = A.class.getDeclaredClasses();
        A outer = new A();
        try {
            for (int i =0; i < classlist.length; i++){
                if (! classlist.getSimpleName().equals("B")){
//skip other classes
continue;
//this is what I mention above.
Constructor constr = classlist[i].getDeclaredConstructor(A.class);
constr.setAccessible(true);
Object inner = constr.newInstance(outer);
Method meth = classlist[i].getDeclaredMethod("testMethod");
meth.setAccessible(true);
//the actual method call
meth.invoke(inner);
} catch (Exception e) {
throw new RuntimeException(e);
Good luck, and if you find yourself relying on this too much, it might mean a code redesign.

Method inheritence from abstract classes, and arguments

I'm trying to do something a little weird. I'm writing a pretty complicated wrapper/adapter for two platforms, and I'd like to have an abstract method passed on to child classes, but with the type of the single argument specified by the child class. Is this possible?
Example
public abstract class AbstractParent {
public abstract void foo([ambiguousType] arg);
public class ChildOne extends AbstractParent {
public void foo(TypeA arg) {
//body
public class ChildTwo extends AbstractParent {
public void foo(TypeB arg) {
//body
}TypeA and TypeB have no common supertype beyond Object, and I'd rather not just do instanceof checks and throw errors. Does anyone know of a solution? Can I elaborate any better?

Perhaps you could use generics?
    public abstract class AbstractParent<E> {
        public abstract void foo(E arg);
    public abstract class ChildOne extends AbstractParent<String> {
        public void foo(String arg) {
    public abstract class ChildTwo extends AbstractParent<Integer> {
        public void foo(Integer arg) {
    }

Access fo Method parameters to Anonymous Class ?

Can somebody please provide some more information on the statement below? I am also searching for some sample code implementations of it. It would help the cause better.
+"Methods of the object of the anonymous class need access to final local variables and method parameters belonging to the method in which the anonymous class is defined. "+
Thanks in Advance

We're concerned here with "local" classes, i.e. classes defined inside methods (not all anonymous classes are local, and not all local classes are anonymous).
The thing about local classes is that, unlike local variables etc., instances of a local class may survive the method returning. For example a local class might be a listener which gets added to a swing component, it could be a Runnable that get's launched as a thread.
Local classes get to access local variables and parameters of the method in which they are declared but the variables or parameters have to be declared final because, since the class needs to be able to access the value of the local variable even after the method exits, and the variable ceases to exist, what actually happens it that the value of the variable is copied into a special field of the anonymous class, and if the variable could be changed after the class was defined, the two copies would then disagree.

Method signature (Chapter : Abstract class and Polymorphism)

Hi all,
I found some quaint thing about signature method. It's said: "A child class may define additional methods with signatures different from the parent's method." but
"It is an error if a child defines a method with the same signature as a parent method, but with a different return type."
The thing is: return type is not belong to method's signature !!!
Can someone explain this point?
Thanks and have a nice day ( 11:00 am in Germany)
H.A

"It is an error if a child defines a method with the
same signature as a parent method, but with a
different return type."
The thing is: return type is not belong to method's
signature !!!
Can someone explain this point?Yes.
Even though return type isn't part of the "signature" (as the JLS defines "signature"), the JLS requires that child methods with the same signature as parent classes have the same return type.
Think about it for a minute: Return type isn't part of the signature, but it is part of the contract. If Parent has public Whatsit foo() then it's promising that every instance of Parent, AND every instance of any Child that is a subclass of Parent (since a Child also IS A Parent), will have that method, and callers of that method will receive a Whatsit as a return value.
If I try to override it in Child with public Doobley foo() then a call might try to do this: Parent parent = factory.createParent(); // happens to return a Child, which is allowed, because a Child is a Parent
Whatsit w = parent.foo(); // OH NO! We got bad a Doobley instead of a Watsit! See the problem?
Now, it turns out that 1.5 adds covariant return types, which allows a child method to return a subtype of what the parent returns. So the above would work IFF Doobley is a subclass or subinterface of Whatsis, or is a class that implements Whatsis. This works because the child is still keeping the parent's contract. He's just actually promising a bit more than what the parent promises.

Accessing a method from an outside Class

I am working on a program that will create an array list and hashmap of 3 shapes--squares,triangles and circles. I have created classes for each shape as well as a class that creates arrays of these shapes (called ShapeGenerator).
Now I need to create a class that will call ShapeGenerator to create the shapes and then put them into an arraylist and hashmap. Right now I just can't get seem to call the methods from ShapeGenerator to create the arrays. What follows is the code I've written. Any guidance would be appreciated. Thanks in advance...
public class ShapeMaker{
     public ShapeMaker(){
public ShapeGenerator[] makeShapes(){
     ShapeGenerator[] myShapeGenerator = new ShapeGenerator();
     myShapeGenerator.createSquares(5);
     return createSquares;
public static void main(String[] args){
     ShapeMaker mySM = new ShapeMaker();
     mySM.makeShapes();
     System.out.println("I made a Shape");
}

ShapeGenerator[] myShapeGenerator = new ShapeGenerator();
new ShapeGenerator will return a single instance of ShapeGenerator - Not an array.
to create a new ShapeGenerator:
ShapeGenerator sg=new ShapeGenerator();
then your method call:
Object squares[]= sg.createSquares(5);
or you could just do:
Object squares[]=new ShapeGenerator().createSquares(5);
makeShapes() should then return an array of Object (or even better do you have a base Shape class?)
So we finally end up with something like:
public class ShapeMaker{
public ShapeMaker(){
public Object[] makeShapes(){
ShapeGenerator myShapeGenerator = new ShapeGenerator();
return myShapeGenerator.createSquares(5);
public static void main(String[] args){
ShapeMaker mySM = new ShapeMaker();
mySM.makeShapes();
System.out.println("I made a Shape");
Excuse any typos but I have not tried to compile this as I don't have a myShapeGenerator etc and I'm too tired (or lazy) to write one.
Good luck.

Abstract Classes and Method

Hi all,
I want to appear for SCJP exam and studying for the same ,
Can anyone tell whether concrete methods in an abstract class can be overridden by its subclass or not ... ???
Thanks in advance ,
Suvo

Hai
Actually the overridden concept is supported when the methods are default, protected, public with some constraints, not only when they are protected and public.
The access specifier in the overriding method (in the derived class) should not be more limiting than that of the overriden method (in the base class). This means that if the access specifier for base class method is protected then the access specifier for the derived class method should not be default or private but can be protected, public. The order of increasing visibility of various specifiers is:
default
protected
public
Thanks,
Hari
Edited by: Hari on Jun 3, 2011 8:45 PM

Protected methods in abstract classes

Hello All
I have some problem which I cannot find a workaround for.
I have three classes:
package my.one;
public abstract class First {
protected void do();
protected void now();
package my.one;
public class NotWantToHave extends First {
protected First obj;
public NotWantToHave(First O) { obj = O; }
public void do() { obj.do(); }
public void now() { obj.now(); }
package my.two;
public class Second extends my.one.First {
protected void do() { System.out.println("Second does"); }
protected void now() { System.out.println("Second does now"); }
package my.three;
public class Three extends my.one.First {
protected my.one.First obj;
public Three(my.one.First O) { obj = O; }
protected void do() { System.out.println("Doing"); }
protected void now() { obj.now(); } // Not possible, see later text
Problem is, as one can read in http://java.sun.com/docs/books/tutorial/java/javaOO/accesscontrol.html , it says that you cannot access protected members and methods from classes if they are in a different package. However, since my class Three should not concern about the method now() but should use from some other class that implements (i.e. class Second), the question I have is how to do?
One way would be to implement a class that simply make a forward call to any protected method in the same package the abstract class is in like in class NotWantToHave and pass it to the constructor of class Third while this class was created with an instance of class Second. However, such a call would look very clumsy (new my.three.Third(new my.one.NotWantToHave(new my.two.Second()));). Furthermore, everyone could create an instance of class NotWantToHave and can invoke the methods defined as protected in class First, so the access restriction would be quite useless.
Does anyone has a good idea how to do?

Hi
One way I found is to have a nested, protected static final class in my super-class First and provide a protected static final method that returns a class where all methods of the super-class are made public and thus accessible from sub-classes at will. The only requirement is that a sub-class must invoke this method to encapsulate other implementations of the super-class and never publish the wrapper class instance. This will look as follows:
package my.one;
public abstract class First {
protected final static class Wrap extends First { // extend First to make sure not to forget any abstract method
    protected First F;
    public void do() { F.do(); }
    public void now() { F.now(); }
    protected Wrap(First Obj) { F = Obj; }
} // end Wrap
protected final static First.Wrap wrap(First Obj) { return new First.Wrap(Obj); }
protected abstract void do();
protected abstract void now();
} // end First*******
package my.two;
public class Second extends my.one.First {
protected void do() { System.out.println("Second does"); }
protected void now() { System.out.println("Second does now"); }
} // end Second*******
package my.three;
public class Three extends my.one.First {
protected my.one.First.Wrap obj;
public Three(my.one.First O) { obj = my.one.First.wrap(O); }
protected void do() { System.out.println("Doing"); }
protected void now() { obj.now(); } // Not possible, see later text
} // end Third*******
In this way, I can access all methods in the abstract super class since the Wrap class makes them public while the methods are not accessible from outside the package to i.e. a GUI that uses the protocol.
However, it still looks clumsy and I would appreciate very much if someone knows a more clear solution.
And, please, do not tell me that I stand on my rope and wonder why I fall down. I hope I know what I am doing and of course, I know the specification (why else I should mention about the link to the specification and refer to it?). But I am quite sure that I am not the first person facing this problem and I hope someone out there could tell me about their solution.
My requirements are to access protected methods on sub-classes of a super-class that are not known yet (because they are developed in the far, far future ...) in other sub-classes of the same super-class without make those methods public to not inveigle their usage where they should not be used.
Thanks

What are abstract classes/methods and what are they for?

Hi,
I've just heard about abstract classes and methods and I'm just wondering what exactly they're used for, and why are they there for the Graphics class for example?
Cheers.

raggy wrote:
bastones_ wrote:
Hi,
I've just heard about abstract classes and methods and I'm just wondering what exactly they're used for, and why are they there for the Graphics class for example?
Cheers.Hey bro, I'll try to solve your problemYou have to know two important concepts for this part. 1 is Abstract classes and the other is Interface classes. Depends on the nature of the project, you need to set certain level of standards and rules that the other developers must follow. This is where Abstract classes and Interface classes come into picture.
Abstract classes are usually used on small time projects, where it can have code implementation like general classes and also declare Abstract methods (empty methods that require implementation from the sub-classes).Wrong, they are used equally among big and small projects alike.
Here are the rules of an Abstract class and method:
1. Abstract classes cannot be instantiatedRight.
2. Abstract class can extend an abstract class and implement several interface classesRight, but the same is true for non-abstract classes, so nothing special here.
3. Abstract class cannot extend a general class or an interfaceWrong. Abstract classes can extend non-abstract ones. Best example: Object is non-abstract. How would you write an abstract class that doesn't extend Object (directly or indirectly)?
4. If a class contains Abstract method, the class has to be declared Abstract classRight.
5. An Abstract class may or may not contain an Abstract methodRight, and an important point to realize. A class need not have abstract methods to be an abstract class, although usually it will.
6. Abstract method should not have any code implementations, the sub-classes must override it (sub-class must give the code implementations). An abstract method must not have any implementation code code. It's more than a suggestion.
7. If a sub-class of an Abstract class does not override the Abstract methods of its super-class, than the sub-class should be declared Abstract also.This follows from point 4.
9. Abstract classes can only be declared with public and default access modifiers.That's the same for abstract and non-abstract classes.

Final methods in abstract classes?

Hi, why is it possible to define a final method in an abstract class? The theory behind a final method doesn't say that a final method couldn't be overridden?
Marco

So it's formally correct but it doesn't have any
sense, does it?You sound very confused. A final method in an
abstract class has just the same semantics and
makes just as much sense as in a non-abstract
class.
The semantics of a final method is simply that
it cannot be overridden in subclassed. Both
abstract and non-abstract classes can be
subclasses. So why do you think there should be any
difference?Actually i was confused now it's clear. I was too binded to the concept that the extending class SHOULD(not for a formal reason, but for a 'design' one) write the implementation of the methods defined in the abstract class. Now i see that, actually, by defining a final method in an abstract class we are defining our design as implemented and clients(i.e. subclasses) can only use it.
Thank you,
Marco

Abstract class and a static method

Can i call a static method within an abstract class ?

public class AbstractDemo {
public static void main(String[] args) {
    BiPlane biPlane = new BiPlane();
    System.out.println("biplane propulsion = " + biPlane.getPropulsionType());
    JumboJet jumboJet = new JumboJet();
    System.out.println("jet load = " + jumboJet.confirmMaxLoad());
    System.out.println("jet speed = " + jumboJet.getTopSpeed());
    System.out.println(Airplane.confirmMaxLoad());
abstract class Airplane {
static String confirmMaxLoad() {
    return "go_get_um, yeehaa!";
public abstract String getPropulsionType();
abstract String getTopSpeed();
class BiPlane extends Airplane {
public BiPlane() {
    System.out.println("BiPlane constructor");
static String confirmMaxLoad() {
    return "400 lbs";
public String getPropulsionType() {
    return "propeller";
final String getTopSpeed() {
    return "130 knots";
class JumboJet extends Airplane {
public JumboJet() {
    System.out.println("JumboJet constructor");
public String getPropulsionType() {
    return "jet";
public String getTopSpeed() {
    return "mach .87";
}

Implement method inside abstract class?

hello everyone:
I have a question regarding implementation of method inside a abstract class. The abstract class has a static method to swamp two numbers.
The problem ask if there is any output from the program; if no output explain why?
This is a quiz question I took from a java class. I tried the best to recollect the code sample from my memory.
if the code segment doesn't make sense, could you list several cases that meet the purpose of the question. I appreciate your help!
code sample
public abstract class SwampNumber
   int a = 4;
   int b = 2;
   System.out.println(a);
   System.out.println(b);
   swamp(a, b);
   public static void swamp(int a, int b)
     int temp = a;
         a = b;
         b = a;
     System.out.println(a);
     System.out.println(b);

It won't compile.
You can't instantiate an abstract class before you know anything.
//somewhere in main
SwampNumber myNum = new SwampNumber();
//Syntax ErrorQuote DrClap
This error commonly occurs when you have code that >>is not inside a method.
The only statements that can appear outside methods >>in a Java class are >>declarations.Message was edited by:
lethalwire

Access overriden method of an abstract class

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