Home/ Questions/Q 876597
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-15T11:27:32+00:00

Possible Duplicate: Weird Java Boxing Recently I saw a presentation where was the following

  • 0

Possible Duplicate:
Weird Java Boxing

Recently I saw a presentation where was the following sample of Java code:

Integer a = 1000, b = 1000;  
System.out.println(a == b); // false  
Integer c = 100, d = 100;  
System.out.println(c == d); // true

Now I’m a little confused. I understand why in first case the result is “false” – it is because Integer is a reference type and the references of “a” and “b” is different.

But why in second case the result is “true”?

I’ve heard an opinion, that JVM caching objects for int values from -128 to 127 for some optimisation purposes. In this way, references of “c” and “d” is the same.

Can anybody give me more information about this behavior? I want to understand purposes of this optimization. In what cases performance is increased, etc. Reference to some research of this problem will be great.

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    I want to understand purposes of this
    optimization. In what cases
    performance is increased, etc.
    Reference to some research of this
    problem will be great.

    The purpose is mainly to save memory, which also leads to faster code due to better cache efficiency.

    Basically, the Integer class keeps a cache of Integer instances in the range of -128 to 127, and all autoboxing, literals and uses of Integer.valueOf() will return instances from that cache for the range it covers.

    This is based on the assumption that these small values occur much more often than other ints and therefore it makes sense to avoid the overhead of having different objects for every instance (an Integer object takes up something like 12 bytes).

    • 0