Question

Consider a third-party class like

class A {
    private int value;
    public int getValue() {
        return value;
    }
    public void setValue(int value) {
        this.value = value;
    }
}

which I make immutable like

final class ImmutableA extends A {
    public ImmutableA(int value) {
        super.setValue(value);
    }
    public void setValue(int value) {
        throw new UnsupportedOperationException();
    }
}

The visibility guarantee for final fields doesn’t apply here. My question is if other threads are guaranteed to see the correct state of ImmutableA.

If not, is there a solution? Using delegation is not an option since I need ImmutableA to be an A.

Answer 1

You could use synchronized, though this may slow down the getter:

final class ImmutableA extends A 
{
    public ImmutableA(int value) {
        synchronized (this) {
            super.setValue(value);
        }
    }

    public void setValue(int value) {
        throw new UnsupportedOperationException();
    }

    public synchronized int getValue() {
        return super.getValue();
    }
}