Monday, June 23, 2008

Wrapper Objects, Autoboxing, ==

Let us look at the following Java code:

Integer lInt1 = 5000;
Integer lInt2 = 5000;
if (lInt1 != lInt2) {
System.out.println("Different Objects");

Integer lInt3 = 100;
Integer lInt4 = 100;
if (lInt3 == lInt4) {
System.out.println("Same Object");

When compiled and run, the output will be:

Different Objects
Same Object

Apparently, in order to save memory, when using autoboxing to create two instances of the Integer (and Short) wrapper objects, they will be always == if the primitive values that they hold are from -128 to 127. Why on earth would the Java gods only allow this to happen for values from that interval, and not make it for any (legal) value possible?

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