Are Java wrapper classes really immutable?

java wrapper
PetrosB picture PetrosB · Nov 7, 2010 · Viewed 15.4k times · Source

Java Wrapper classes are supposed to be immutable. This means that once an object is being created, e.g., 

Integer i = new Integer(5);

its value cannot be changed. However, doing 

i = 6;

is perfectly valid.

So, what does immutability in this context mean? Does this have to do with auto-boxing/unboxing? If so, is there any way to prevent the compiler from doing it?

Thank you

Answer

bmargulies picture bmargulies · Nov 7, 2010

i is a reference. Your code change the reference i to point to a different, equally immutable, Integer.

final Integer i = Integer.valueOf(5);

might be more useful.

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