Overriding of Abstract Method in Java

Question

Abstract method's property is that it doesn't have body, and so when concrete class extends abstract class, it must implement that abstract method.

So my question is how can an abstract method can be overridden when it doesn't have a body? Isn't it implemented, not overridden?

You should have gone through the tutorial before asking such basic stuff http://docs.oracle.com/javase/tutorial/java/IandI/abstract.html — AurA, Jul 03 '13 at 07:43
http://stackoverflow.com/questions/1005898/java-should-i-add-an-override-annotation-when-implementing-abstract-methods — sanbhat, Jul 03 '13 at 07:43

darijan · Answer 1 · 2015-12-23T12:31:16.933

12

Abstract class with an abstract method.

The method is also marked with abstract and has no body.

public abstract class A {
    public abstract void method();
}

Concretization in the class B that extends abstract class A. Also, the method loses the abstract keyword and gets the body.

public class B extends A {
    @Override
    public void method() {
        System.out.println("Hello");
    }
}

edited Dec 23 '15 at 12:31

answered Jul 03 '13 at 07:42

darijan

9,725
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Here non abstract method overriding a abstract method so i am little bit confuse about it. – user2151689 Jul 03 '13 at 08:54
Yes, `abstract` is a kind of a "sign" that this method **must** be overridden in some of the future methods. A method that overrides must have tame same method signature, but lose the `abstract` keyword. – darijan Jul 03 '13 at 08:59

score 3 · Answer 2 · answered Jul 03 '13 at 07:44

public abstract class BaseClass {
    public abstract void doSomething();
}

public class ConcreteClass extends BaseClass {
    @Override
    public void doSomething() {
        System.out.println("Hi!");
    }
}

public class AnotherConcreteClass extends BaseClass {
    @Override
    public void doSomething() {
        System.out.println("Hello!");
    }
}

The implementation of the doSomething method that gets executed will depend on the runtime type of the object you are calling doSomething upon.

score 2 · Answer 3 · answered Jul 03 '13 at 07:42

Just by providing an implementation for the method , provide it with a body.

public abstract class Base {
   public abstract void someMethod(); // no implementation here
}

public class Sub extends Base {
   @Override
   public void someMethod() {
    //It is Overridden
   }
}

score 2 · Answer 4 · answered Jul 03 '13 at 07:44

2

public abstract class A {  
    public abstract String getValue();
}

public class B extends A {

    @Override
    public String getValue(){
        return "I'm Overriden";
    }
}

It's the same like in any other class.

answered Jul 03 '13 at 07:44

ssindelar

2,833
1
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36

score 1 · Answer 5 · answered Jul 03 '13 at 07:42

When you are implementing a superclass method in subclass, it will override. So Even if the superclass method is abstract, if you implement it in subclass, then it will override it.

So,

public class SuperClass{
   public abstract void someMethod();
}

 public class SubClass{
   public void someMethod(){

           System.out.println("subclass method");

   }
 }

score 1 · Answer 6 · answered Jul 03 '13 at 07:42

1

Foo.java

public abstract class Foo {
  public abstract void doStuff();
}

Bar.java

public class Bar extends Foo {
    @Override
    public void doStuff() {
        // doStuff
    }
}

answered Jul 03 '13 at 07:42

tom

18,953
4
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35

score 1 · Answer 7 · answered Jul 03 '13 at 07:42

1

Abstract method can be overridden just like overriding other normal methods, by providing an implementation.

answered Jul 03 '13 at 07:42

aksh1t

5,410
1
37
55

score 1 · Answer 8 · answered Jul 03 '13 at 07:43

1

This is the same as any other method override:

public abstract class AbstractClass {
    public abstract void abstractMethod();
}

...

public class ConcreteClass {

    @Override
    public void abstractMethod() {
        ....
    }
}

answered Jul 03 '13 at 07:43

robjohncox

3,639
3
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Overriding of Abstract Method in Java

8 Answers8