equals on array

[Edmen Tay]

Hi, My question from Inquisition (SCJP5 quiz by Mark Dechamps).

  
int[]a = new int[]{1};
int[]b = new int[]{1};
System.out.println(a.equals(b));//return false
  

The answer is false. Can anyone explain?

When I try,

  
        Integer c = new Integer(1);
        Integer d = new Integer(1);
        System.out.println(c.equals(d));//return true
  

Many thanks,

Edmen.

[Ruben Soto]

It seems equals is not overridden for arrays, which means that equals in the case of arrays will be testing for object identity. However, wrappers do override equals, and two instances of a wrapper class are equal if they are both instances of the same class, and if the values they hold are equal.

[Edmen Tay]

Alright, I think i got what you trying to meant.

for array, it is not overriden and it will run,

  
    public boolean equals(Object obj)
    {
        return this == obj;
    }

for wrapper class, it will be overriden and will run,

  
    public boolean equals(Object obj)
    {
        if(obj instanceof Integer)
            return value == ((Integer)obj).intValue();
        else
            return false;
    }

Please correct if i am wrong.

Many thanks.

Edmen.

[Ruben Soto]

Edmen, I think you got it!

[Ruben Soto]

I forgot to say that there are a couple of methods in the java.util.Arrays class that do what you want:

static boolean equals(Object[], Object[])
and
static boolean equals(primitive[], primitive[])

(K&B, p. 593)

[Wouter Oet]

To compare int[] you can use the equals function in the Arrays class.
, int[])]Arrays

[Punit Singh]

Edmen, did you try this one ?

Integer c = new Integer(128);
Integer d = new Integer(128);
System.out.println(c.equals(d));

[Ruben Soto]

Punit, are you thinking of the equality (==) operator? That's the one that has the restriction for the Integer type of -128 to 127. This case would be no different for equals than the other case.

I forgot to mention that for the == operator to report equal on the Integer objects it is also necessary that they have been created through autoboxing, and not via the new() operator. The new operator will always create a new object on the heap (similar to what happens with Strings and the constant pool.)
[ December 29, 2008: Message edited by: Ruben Soto ]

[Punit Singh]

Ya this restriction is for == operator, I forgot the case, actually I had raised this question for == operator.

[Edmen Tay]

Hi Punit,

Integer c = new Integer(128);
Integer d = new Integer(128);
System.out.println(c.equals(d));

It is true.

Integer MAX VALUE is 2147483647 and MIN VALUE is -2147483648

Edmen