Immutability

Immutable objects are always thread safe. [1]

Cases

• No fields at all.

class StatelessAdder
{
    public int add(int a, int b) { return a+b;}
}

• Only final fields

class ImmutableAdder
{
    private final int offset;

    public ImmutableAdder(int a) { offset = a;}

    public int addOffSet(int b) { return offset+b;}
}

Applications

• Abstract data types: Immutable objects can serve as instances of simple abstract data types representing values.
• Value containers: Immutable objects can be used when it is necessary to establish some consistent state once and then rely on it foever more.
• Sharing: Immutable objects are useful for sharing, since there are not any concerns about synchronization or access resitrction.

Bibliography

1. Doug lea