Does Java return by reference or by value

Question

I have a HashMap:

private HashMap cardNumberAndCode_ = new HashMap();

And later I do this:

Answer 1

The Integer variable contains a reference to an Object. The Integer object is immutable and you cannot change it. When you perform

balance = 10; // replace the previous Integer reference with a different one.

The normal way to do this is to use

cardNumberBalance_.put(cardNumber, 10);

An alternative which is not used so often is to use AtomicInteger or use your own MutableInteger

private final Map cardNumberAndCode_ = new HashMap();

AtomicInteger balance = cardNumberBalance_.get(cardNumber);
balance.set(10);