This and Super keyword

[Prashant Ameta]

Hii , m quite new to the Java world and m looking for some very general examples,actually explaination for "This" and "Super" key words!!!i hav a book but it looks very BOOKISH

Thanks and Regards
Prashant Ameta

[John McClellan]

If you're really new to programming in general, not just Java, this may be a topic you'll want to cover later. this refers to the object that the method using that keyword is a part of, and in a way, so does super. However this uses the regular class basically, whereas super uses the base class.

public class A {
    public int num() {
        return 0;
    }
}

public class B extends A {
    public int num() {
        return 1;
    }

    public int numSwitch(boolean useBase) {
        if (useBase) {
            return super.num();
        } else {
            return this.num(); // or it could be return num(); - same thing
        }
    }
}

[Bear Bibeault]

this and super. Case counts!

[Bill Gorder]

this - a final reference to the current object. Can be used in any non-static context for example inside the body of an instance method.

there is also the this() construct. This is useful for overloading constructors. this() must be the first statement in a constructor and will invoke the local constructor with a corresponding parameter list.

super() is used in a subclass to invoke the superclass constructor with a corresponding parameter list. super() must also be the first statement in a constructor.

So in short this() is used for chaining local constructors when super() chains subclass constructors to superclass constructors.

[Campbell Ritchie]

I think you have been given examples of most of their uses, and welcome to the Ranch

[salvin francis]

Checkout another usage of "this" keyword:

  class SomeOtherBase {

    long someVariable = 10; //-- SomeOtherBase

    public void display() {}
  }


  class BaseClass {

    long someVariable = 300; // -- BaseClass

    public void testMethod() {
      new SomeOtherBase() {

        @Override
        public void display() {
          // Access BaseClass variable :
          long value = BaseClass.this.someVariable;

          // Access SomeOtherBase class variable :
          value = this.someVariable;

        }
      };
    }
  }

[Campbell Ritchie]

Do you need BaseClass.this there? I thought you only used ClassName.this inside inner or nested classes.

[Prashant Ameta]

thanks alot BEar,Sherrif and Mr.Gorder
thanks a ton JOhn and Salvin....thats exactly what i was looking for.
and now i know how to ask questions...

[salvin francis]

Campbell Ritchie wrote:Do you need BaseClass.this there?

Yes, since we want to access the someVariable from BaseClass

Campbell Ritchie wrote:I thought you only used ClassName.this inside inner or nested classes.

My program works


Checkout this program:

class SomeOtherBase {

	public void display() {}


	public void someMethod(){
		System.out.println("This is Method within SomeOtherBase");
	}

}


class BaseClass {

	public void someMethod(){
		System.out.println("This is Method within BaseClass");
	}

	public void testMethod() {
		SomeOtherBase sob =	new SomeOtherBase() {

			@Override
			public void display() {
				// Access BaseClass method :
				BaseClass.this.someMethod();

				// Access SomeOtherBase class method :
				this.someMethod();

			}
		};
		
		sob.display();
	}
	
	
	public static void main(String args[]){
		System.out.println("In main");
		new BaseClass().testMethod();
	}
}

/*
>java BaseClass
In main
This is Method within BaseClass
This is Method within SomeOtherBase
>Exit code: 0
*/

[Campbell Ritchie]

salvin francis wrote: . . . My program works . . .

Wrong response.

The correct response is to point out what I missed, that you are actually inside an inner class. Sorry for my mistake.