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Guys can anybody explain me this nature of new and the use of Integer 

Integer i = new Integer(-10);
Integer j = new Integer(-10);
Integer k = -10;
Integer l=-10;
System.out.println(i==j);
System.out.println(k==l);

answer is false true

next 

    Integer a=128;
    Integer b=128;
    Integer c=127;
    Integer d=127;
    System.out.println(a==b);
    System.out.println(c==d);

answer am getting is false true. Can anybody explain this nature. thanks in advance :)

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In your first example, you're always creating new Integer objects and assigning those references to i and j. For k and l you're using autoboxing, which sometimes creates new objects and sometimes doesn't.

In your second example, you're just using autoboxing - but with different values, which demonstrates the "sometimes" from above.

From section 5.1.7 of the JLS:

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

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 char and short values, as well as int and long values in the range of -32K to +32K.

于 2012-07-31T08:31:07.820 回答