Integer Wrapper class comparison with == and !=

[Abhijeet Seal]

Hi All,

I have following code :

class d{
	public static void main(String arg[]){

	Integer i1 = 1000;
	Integer i2 = 1000;
	if(i1 != i2) System.out.println("different objects");

	Integer i3 = 10;
	Integer i4 = 10;
	if(i3 == i4) System.out.println("same object");
	
}

}

It gives following output:

different objects
same object.

My question is why is i1!=i2 is true and i3 == i4 also true. because both i1 and i2 have same values and i3 and i4 have same values, so any one of the if conditions should be false .
I am confused here, please help.


Thanks,
Abhijeet

[Jeanne Boyarsky]

Abhijeet,
Welcome to CodeRanch! This is a great question.

Java optimizes by reusing the same object for smaller numbers. Any Integer objects below 256 use the same object. That's why it works for 10. It is a number smaller than 256.

[Abhijeet Seal]

Thanks Jeanne

[Jesper de Jong]

Actually, it's not 256, as Jeanne says. Class Integer caches Integer objects with values between -128 and 127 (by default - it's possible to change this with a system setting).

Abhijeet Seal wrote:because both i1 and i2 have same values and i3 and i4 have same values, so any one of the if conditions should be false .

The == operator only checks if the things on the left and right side of the == refer to the exact same object. It does not look at the what value the object contains.