What are the benefits of IntegerCache while using Integer? [duplicate]

Question

In Integer class, there is private static class IntegerCache.

What is the use of this class?

What are the benefits of it while using Integer?

Answer 1

Values between -128 and 127 are cached for reuse. This is an example of the flyweight pattern, which minimizes memory usage by reusing immutable objects.

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Beyond being an optimization, this behaviour is part of the JLS, so the following may be relied upon:

Integer a = 1;
Integer b = 1;
Integer c = 999;
Integer d = 999;
System.out.println(a == b); // true
System.out.println(c == d); // false