100 == 100 but 1000 != 1000 - what's going on? [boxing, ==, and equals()]

[Piotr Milewski]

I read K&B. Page 235 and 236, but it's not essential info.

I wrote something similar like their code. I'm confused.

Why:

Integer i1 = 100;
Integer i2 = 100;
System.out.println("== : " + (i1 == i2));
System.out.println("!= : " + (i1 != i2));
System.out.println("i1.equals(i2) : " + (i1.equals(i2)));

produces:
== : true
!= : false
i1.equals(i2) : true

and

Integer i1 = 1000;
Integer i2 = 1000;
System.out.println("== : " + (i1 == i2));
System.out.println("!= : " + (i1 != i2));
System.out.println("i1.equals(i2) : " + (i1.equals(i2)));

produces:
== : false
!= : true
i1.equals(i2) : true


[ September 21, 2007: Message edited by: Piotr Milewski ]
[ September 21, 2007: Message edited by: Piotr Milewski ]

[Vinayagar Karpagam]

Hi,

The integer values from -128 to 127 are stored into a pool just like String pool. So, for those values, when you do Integer i1 = 100; it is actually Integer.valueOf(100); which creates an Integer object with value as 100 and adds it to the pool. When Integer i2 = 100; is executed, an Integer object with value as 100 will be available in the pool and that will be used.

Hope this helps.
[ September 21, 2007: Message edited by: Vinayagar Karpagam ]

[ahmed yehia]

Integer literals between -128 and 127 will result true comparing with ==.

[Piotr Milewski]

Thanks a lot.

So this "integer pool" contains only values between -128 and 127, correct? (not between 0 and 127) Am I correct?

[Collins Mbianda]

Per Java Language Specification

If the value p being boxed is true, false, a byte, a char in the range \u0000 to \u007f, or an int or short number between -128 and 127, then let r1 and r2 be the results of any two boxing conversions of p. It is always the case that r1 == r2.

[Piotr Milewski]

Thanks, that's enough to finish this case successfully

Thanks a lot!