public class LazyImmutableObject<E> {

    private E object;

    public LazyImmutableObject() {

    }

    public LazyImmutableObject(E object) {
        try {
            set(object);
        } catch (ImmutableObjectException e) {
            e.printStackTrace();
        }
    }

    public synchronized void set(E object) throws ImmutableObjectException {
        if(object != null)
            throw new ImmutableObjectException("You cannot define a value after it has been set");
        this.object = object;
    }

    public synchronized E get() {
        return object;
    }
}

class ImmutableObjectException extends Exception {

    private static final long serialVersionUID = 1L;

    public ImmutableObjectException(String string) {
        super(string);
    }
}