Why this Output?

[Swati Kadam]

abstract class GreaterOne {
abstract void doSomething () ;
};
 
class Test {
 
GreaterOne doSomething ( ) {

class Inner extends GreaterOne {
 
void doSomething ( ) {
System . out .println ( " I Am Weasel " ) ;
}
};
return new Inner ( ) ;
}
};
 
class ZZY {
 
public static void main ( String ka  [ ] ) {
Test t = new Test ( ) ;
GreaterOne g = t . doSomething ( ) ;
g . doSomething ( ) ;
}
};

Output of this program is I am Weasel...
After callin g.doSomething(); not output is displayed for this call....
Why is it so?


[BSouther: Added UBB CODE tags]
[ March 05, 2008: Message edited by: Ben Souther ]

[marc weber]

Well, it's not for lack of spaces or semicolons.

There are two methods here called "doSomething," but these are entirely different methods.

In the class Test, doSomething() creates an instance of Inner. A reference to that instance is upcast to type GreaterOne and returned by the method. Nothing is output.

In the class Inner, doSomething() prints "I Am Weasel."

[Uttara Rishi]

I still dont get it!

 
 
GreaterOne doSomething ( ) {
 
class Inner extends GreaterOne {
 
void doSomething ( ) {
System . out .println ( " I Am Weasel " ) ;
}
}
return new Inner ( ) ;
}
}
 
class ZZY {
 
public static void main ( String ka [ ] ) {
Test t = new Test ( ) ; //Line 1
GreaterOne g = t . doSomething ( ) ; // Line 2
g . doSomething ( ) ;  // Line 3
}
}
 
 
   

Line 1 : Instantiates a new Test object.

Line 2: Calls the doSomething() method which prints "I am a Weasel".

Line 3 : Does nothing!!!

In the class Test, doSomething() creates an instance of Inner. A reference to that instance is upcast to type GreaterOne and returned by the method. Nothing is output.

I dont get it!! Why is the output not executed?
Can somebody please explain?


Uttara Rishi
[ March 05, 2008: Message edited by: Uttara Rishi ]

[marc weber]

Originally posted by Uttara Rishi:
...Line 2: Calls the doSomething() method which prints "I am a Weasel".

Line 3 : Does nothing!!!...

No, line 2 does not result in any output. Line 2 calls doSomething in Test. That method contains a local class definition for Inner. But all the method does is create a new instance of Inner (based on the local definition) and return a reference.

Line 3 uses the reference to call doSomething in Inner, and that is where the output occurs.

abstract class GreaterOne {
  abstract void doSomething();
}
 
class Test {
  GreaterOne doSomething() {
    System.out.println(" Entered doSomething of Test.");
 
    //START LOCAL CLASS DEFINITION
    class Inner extends GreaterOne {
      void doSomething() {
        System.out.println(" Entered doSomething of Inner.");
        System.out.println(" I Am Weasel.");
        System.out.println(" Leaving doSomething of Inner.");
      }
    }
    //END LOCAL CLASS DEFINITION
 
    System.out.println(" Leaving doSomething of Test.");
    return new Inner();
  }
}
 
class ZZY {
  public static void main(String[] ka) {
    Test t = new Test();
    System.out.println("In main, calling t.doSomething...");
    GreaterOne g = t.doSomething();
    System.out.println("In main, calling g.doSomething...");
    g.doSomething();
  }
}

[marc weber]

Again, there are 2 separate doSomething() methods.

In Test, doSomething() is basically just...

GreaterOne doSomething () {
    //Inner class definition
    return new Inner();
}

In Inner, doSomething() is just...

void doSomething() {
    System.out.println("I Am Weasel.");
}

[Uttara Rishi]

Thanks marc .I got it!!

[Swati Kadam]

By commenting out which line will the following class compile with no errors ?

class ZZY {

transient final int i = 0;
transient final static int j = 10 ;
int k = 78 ;

char jack(){
return 'a';
}

public static void main ( String args [ ]) { // ---> 1
new ZZY ( ) . jack ( ) ; // ---> line 2
int d = new ZZY ( ) . j + new ZZY ( ) . i ; // ---> line 3
new ZZY ( ) . k ; // ---> line 4
System.out.println(newZZY().i+" "+new ZZY().j);//--> line 5
}
}


In this program you have to comment line 4...
new zzy().K; In this line new ZZY() returns object of class zzy and you can access any instance variable as object.varname...
but here why we cant access it?

[marc weber]

Originally posted by Swati Kadam:
...you can access any instance variable as object.varname...
but here why we cant access it?

The reference is fine. The problem is that you're not doing anything with that line, so it's not a statement. If you use this reference in a complete statement, then it's fine. For example...

int x = new ZZY().k;

[Nadeem Khan]

Basically what you meant to say was that you cannot access a mehtod local inner class's methods from outside that method where its defined. am i right marc?