Abstract Methods

[Vishnu Munnangi]

Hi every one,

In one of the mock exams i came over this question...

Abstract method cannot be final. True or False ?

The answer given is True.

In some book i read that abstract methods can have final methods, in which case the subclasses of the abstract class need not give implementation to those methods which are declared as final in the base class.

Can any one clarify this...

Thanks in advance

[Vishnu Munnangi]

I just executed the program and i got compile time error that illegal combination of modifiers static and abstract.

I should have asked this question after compiling the program.

Sorry for the inconvenience

[Anthony Villanueva]

Originally posted by vishnu priya parimi:
Abstract method cannot be final. True or False ?

It also helps to consult the
JLS.

[Peixiao Lin]

True. Abstract class need to be implemented by subclass, so can not be final. But it can have non-abstract methods in it which can be declared as final if you don't want subclass override those methods or make them abstract.

[Jeroen Wenting]

An abstract CLASS can have final methods.
An abstract METHOD can not be final.

Abstract means: MUST be implemented by subclasses
Final means: MAY NOT be implemented by subclasses.

Thus abstract final would mean: MUST be implemented but MAY NOT be implemented by subclasses, which is impossible.

Therefore the combination is not allowed.

As an abstract class can have non-abstract methods, some of those methods may be final.

[Thomas Drew]

The following code did compile and run. I declared the final varible as private. It appears that you can place a final varible in an abstract class if it is declared as private.

/*
 * foo.java
 *
 * Created on October 7, 2004, 7:34 AM
 */
 
 
public class foo extends foo2 {
    
    /** Creates a new instance of foo */
    public foo() {
    }
    public static void main(String args[]){
     foo newfoo = new foo();
     newfoo.dosomething();
    }
}
 
abstract class foo2 {
    private final int minifoo= 3;
    int minifoo3;
    
    public void dosomething() {
     System.out.println("I'm Doing something"); 
      
    }
    
}
 

([C0DE][/C0DE] tags added.)
[ October 07, 2004: Message edited by: Barry Gaunt ]

[Barry Gaunt]

suri, please read our Javaranch Naming Policy and change your displayed name to comply with it. Please use two names in the format <first name> <family name>.

Thankyou
-Barry

[David Ulicny]

Because private are not inherited.

[Barry Gaunt]

Thomas, you can place any final variable of any access specification (public, private, protected, default) in a abstract class:

public abstract class Abstract
{
    public final int x = 42;
    protected final int z = 42;
    final int w = 42;
    private int v = 42;
 
    public int sampleMethod(int y)
    {
        return x + y;
    }
}