what is dereference?

[dolly shah]

public class Autobox2 {
    public static void main(String...args){
        Float A=9.0f;
        float a=(float)9.0;
        System.out.println(A.equals(a));
        System.out.println(a.equals(A));//line 1 
        System.out.println(a<=A);
        System.out.println(A<=a);
    }
}

This example is from Whizlabs. This code wont compile. The reason they have given is at line 1 we are attempting to dereference the primitive type float. I even heard "deference" word first time. Can anyone please help me?

[Raghavan Muthu]

I know one such term 'dereferencing' with respect to 'C'/'C++' Pointers, which actually means 'taking out the value stored in a particular memory address being pointed to by this pointer value'.

If, p is a pointer to an integer and it can be used as follows.

  int i, *p;
  p = &i;
  i = 5;
  i++;  // incrementing the value of 'i' directly
  ([B]*p[/B])++; // incrementing the value of 'i' indirectly through its pointer
        // by [B]dereferencing[/B] the pointer variable

Here, they would have meant to say the same 'unboxing' i think. As, boxing and unboxing are the means to convert your primitive to wrappers and vice versa.

does that help dolly shah?
[ October 08, 2007: Message edited by: Raghavan Muthu ]

[marc weber]

Variables do not hold objects. Instead, variables hold references to objects.

So myVariable is just a reference -- not the object itself. But in order to call a method, we need the actual object. The dot operator "dereferences" the variable and "gets" the object.

myVariable.myMethod();
          ^
          |
          dot operator [B]dereferences[/B] the variable holding a reference
          and gives us an object that we can call a method on

However, a primitive variable holds the actual value. It does not just reference it. Therefore, primitive variables cannot be dereferenced. So if you try to use the dot operator on a primitive variable, you will get the "cannot be dereferenced" error.

[dolly shah]

Thanks marc. I did not know this before.