Why is avoiding Boolean instantiation a good idea?

Question

PMD is warning me to avoid Boolean instantiation (for efficiency reasons). I have something like this

Boolean variable = new Boolean(somestringIGotRepresentingABoolean);

And I'm supposed to use this

Boolean variable = Boolean.valueOf(somestringIGotRepresentingABoolean);

Why is that better?

Answer 1

The reason is that new Boolean always returns a new instance. Since Boolean instances are immutable it does not make sense to have more than 2 instances. One for false and one for true.

Try this and you will see

Boolean boolean1 = new Boolean("true");
Boolean boolean2 = new Boolean("true");
Boolean boolean3 = new Boolean("true");

System.out.println(System.identityHashCode(boolean1));
System.out.println(System.identityHashCode(boolean2));
System.out.println(System.identityHashCode(boolean3));

Boolean valueOf1 = Boolean.valueOf("true");
Boolean valueOf2 = Boolean.valueOf("true");

System.out.println(System.identityHashCode(valueOf1));
System.out.println(System.identityHashCode(valueOf2));