Compare 2 Integer under 128

Question

    Integer a = 127;
    Integer b = 127;
    System.out.println(a == b);

The result is true, but:

    Integer a = 128;
    Integer b = 128;
    System.out.println(a == b);

The result is false. Why?

Answer 1

You shouldn't compare objects this way in Java. When you compare them like a == b, you compare references but not values.

You should use equals method.

Integer a = 127;
Integer b = 127;

System.out.println(a.equals(b));

If you ask why is this happening for integers under 128: Java uses pools for small values. So, all integers under 128 do not create new instances but use "pooled", cached one.

This question is actually has been asked on SO. Read these articles:

• Why does 128==128 return false but 127==127 return true when converting to Integer wrappers?
• JAVA: Comparison not working when Integer larger than 128
• Why equal operator works for Integer value until 128 number?