2007-10-28 - きしだのはてな

Integer a = 130;
Integer b = 130;
System.out.println(a == b);
の場合は、falseになります。

2007-10-28 - きしだのはてな

一応、言語仕様的には

Discussion

Ideally, boxing a given primitive value p, would always yield an identical reference. In practice, this may not be feasible using existing implementation techniques. The rules above are a pragmatic compromise. The final clause above requires that certain common values always be boxed into indistinguishable objects. The implementation may cache these, lazily or eagerly. For other values, this formulation disallows any assumptions about the identity of the boxed values on the programmer's part. This would allow (but not require) sharing of some or all of these references. This ensures that in most common cases, the behavior will be the desired one, without imposing an undue performance penalty, especially on small devices. Less memory-limited implementations might, for example, cache all characters and shorts, as well as integers and longs in the range of -32K - +32K.

Java SE Specifications

とあるのでSunの実装がそうなだけで
他の実装や今後は変わる場合がありますよ♪

まぁ、きしださんの言うとおり
ちゃんと意識して注意して使えば便利なので
問題ないとは思いますが