instanceof doubt

[aslika bahini]

Hi,

  
interface Foo
{

}
class A implements Foo
{

}
class BinstanceTest extends A
{
  A a = new A();
  BinstanceTest b = new BinstanceTest();
  public static void main(String args[])
  {
   BinstanceTest bobj = new BinstanceTest();
   boolean test1,test2,test3;
   test1 = bobj.a instanceof Foo;
   test2 = bobj.b instanceof A;
   test3 = bobj.b instanceof Foo;
   System.out.println(" "+test1+" "+test2+" "+test3);
  }
}
  

can any explain why the above code throws exception
(Exception in thread "main" java.lang.StackOverflowError)


Thanks in Advance
samura

[Manfred Klug]

Hi samura,

the problem is the b variable in BinstanceTest. When you instantiate a BinstanceTest, a second BinstanceTest is instantiated to initialize the b variable which instantiates a BinstanceTest to initialize the b variable which ...

BinstanceTest bobj = new BinstanceTest()
  BinstanceTest b = new BinstanceTest()
    BinstanceTest b = new BinstanceTest()
      BinstanceTest b = new BinstanceTest()
        BinstanceTest b = new BinstanceTest()
          ...

[aslika bahini]

Thanks Manfred,

   
        interface Face{}
        class Bar implements Face{}
        class Foo extends Bar{}
       

Operands and Results Using instanceof Operator

In pg 286 (k&B book) table 4.1

I didn't get the 5th row..

1st operand = Foo[]
instanceof operand = Foo,Bar,Face
result = false

why the result is false?

Thanks!
samura

[ August 23, 2007: Message edited by: samura babu ]
[ August 23, 2007: Message edited by: samura babu ]

[Akhilesh Trivedi]

First operand is an array of object and second operand is the object itself.

MyClass obj;
MyClass arrObj[];

You can not compare obj with arrObj. However comparison between "arrObj[someIndexHere]" and "obj" would be legal.
[ August 23, 2007: Message edited by: Akhilesh Trivedi ]

[Akhilesh Trivedi]

Originally posted by Manfred Klug:
Hi samura,

the problem is the b variable in BinstanceTest. When you instantiate a BinstanceTest, a second BinstanceTest is instantiated to initialize the b variable which instantiates a BinstanceTest to initialize the b variable which ...

BinstanceTest bobj = new BinstanceTest()
  BinstanceTest b = new BinstanceTest()
    BinstanceTest b = new BinstanceTest()
      BinstanceTest b = new BinstanceTest()
        BinstanceTest b = new BinstanceTest()
          ...

That was really deadly manfred, good catch.

Samura! Good practice would be to have member variable declarations in the class, and initializations at the place/constructor/methods where they are necessary.

[aslika bahini]

Thanks Akhilesh!


regards
samura