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Thread: Why and where abstract methods & classes and static methods are used?

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    Default Why and where abstract methods & classes and static methods are used?

    Hello to all ,
    Actually I know how to declare and implement abstract method's and classes and static method's,
    But the confusion is that where is exactly used ?? as i got this question in interview also,
    just wanna know where it is exactly used and why is needed .
    as we declare abstract method in super class and implement in subclass ,but we can do this in subclass also without declaring in super class why and where is needed,
    please reply me soon??


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    Default Re: Why and where abstract methods & classes and static methods are used?

    By declaring an abstract method in an abstract class and then inheriting the abstract method, you are able to create many different implementations of one method and invoke that method in your code without having to know what subclass you are invoking it on. Alternatively, you can use a non-abstract method to call an abstract method, which when you implement it will have a proper algorithm.

    For example, look at the code below (will not compile as is since classes were not created properly, but the rest of it would work):
    public abstract class A {
    	public int getValue() {
    		return calculate(5);
    	}
    	public abstract int calculate(int n);
    }
     
    public class B extends A{
    	@Override
    	public int calculate(int n) {
    		return n+5;
    	}
    }
     
    public class C extends A{
    	@Override
    	public int calculate(int n) {
    		return n+10;
    	}
    }
     
    public class Runner {
    	public static void main(String args[]) {
    		A obj1 = new B();
    		A obj2 = new C();
     
    		//Call obj1's implementation
    		System.out.println(obj1.calculate(7)+" equals 12");
    		System.out.println(obj1.getValue()+" equals 10");
    		//Call obj2's implementation
    		System.out.println(obj2.calculate(7)+" equals 17");
    		System.out.println(obj2.getValue()+" equals 15");
     
    		//Add both objects to an array
    		A[] objects = new A[2];
    		objects[0] = obj1;
    		objects[1] = obj2;
     
    		//Print the getValue() method of each object in the array
    		for(int i=0;i<objects.length;i++) {
    			System.out.println(objects[i].getValue());
    		}
    	}
    }

    That code will produce the output:
    12 equals 12
    10 equals 10
    17 equals 17
    15 equals 15
    10
    15
    I'll let you read over that. If you need anything clarified, feel free to ask.
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    Default Re: Why and where abstract methods & classes and static methods are used?

    I'd start by defining each.
    Useful links: How to Ask Questions the Smart Way | Use Code Tags | Java Tutorials
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    Default Re: Why and where abstract methods & classes and static methods are used?

    Please read the forum rules. I have merged your duplicate thread. You've got two people replying to your same question in different locations - not very considerate of the volunteers time.

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    Default Re: Why and where abstract methods & classes and static methods are used?

    And post #4 applies not just to double posts in a single forum, but to cross posts as well.

    This thread has been cross posted here:

    http://www.java-forums.org/advanced-java/61365-why-where-abstract-methods-classes-static-methods-used.html

    Although cross posting is allowed, for everyone's benefit, please read:

    Java Programming Forums Cross Posting Rules

    The Problems With Cross Posting


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    Red face Re: Why and where abstract methods & classes and static methods are used?

    an abstract method have no body while the body of the abstract method is in some other class.
    abstract class provide default functionality for the subclass.
    Last edited by captain kashif; July 13th, 2012 at 02:37 PM.

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    Default Re: Why and where abstract methods & classes and static methods are used?

    Hi aussiemcgr ..Thank you for your instant help..
    I'm getting exactly, what u said..but can you give me some real world example of abstract method and classes that where it is used,
    I mean like where it has to be needed to get abstract method & classes,..??

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    Default Re: Why and where abstract methods & classes and static methods are used?

    I provide an example of why and where for abstraction here.
    Last edited by helloworld922; July 14th, 2012 at 01:48 AM.

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