如何删除用作侦听器的lambda表达式/方法句柄？

Question

Java 8引入了lambda表达式,这是一件好事.但现在考虑重写这段代码:

class B implements PropertyChangeListener {
    void listenToA(A a) {
        a.addPropertyChangeListener(this);
    }

    void propertyChange(PropertyChangeEvent evt) {
        switch(evt.getPropertyName()) {
            case "Property1":
                doSomething();
                break;
            case "Property2":
                doSomethingElse();                case "Property1":
                doSomething;
                break;

                break;
    }

    void doSomething() { }
    void doSomethingElse() { }
}

class A {
    final PropertyChangeSupport pcs = new PropertyChangeSupport(this);

    void addPropertyChangeListener(PropertyChangeListener listener) {
        pcs.addPropertyChangeListener(listener);
    }

    void removePropertyChangeListener(PropertyChangeListener listener) {
        pcs.removePropertyChangeListener(listener);
    }
}

随着lambda表达式和方法的引用,它已不再是需要有B落实PropertyChangeListner,我们可以写

class B {
    void listenToA(A a) {
        // using method reference
        a.addPropertyChangeListener("Property1", this::doSomething);
        // using lambda expression
        a.addPropertyChangeListener("Property2", e -> doSomethingElse());
    }

    void doSomething(PropertyChangeEvent evt) { }
    void doSomethingElse() { }
}

class A {
    final PropertyChangeSupport pcs = new PropertyChangeSupport(this);

    void addPropertyChangeListener(String name, PropertyChangeListener listener) {
        pcs.addPropertyChangeListener(name, listener);
    }

    void removePropertyChangeListener(String name, PropertyChangeListener listener) {
        pcs.removePropertyChangeListener(name, listener);
    }
}

我认为新代码不仅更短,而且更简洁,更易于理解.但是在阅读了这里给出的答案之后(这个问题的副本,但我认为问题和答案更加清晰),我看不出有办法实现一个stopListening()可以再次删除监听器的方法.

我确信我不是第一个偶然发现这一点的人.那么有没有人找到一个很好的解决方案,如何使用方法句柄,如本例所示,并仍然能够在以后再次删除侦听器？

UPDATE

那很快.在Mike Naklis和Hovercraft Full Of Eels的答案的基础上,我最终得到了这个:

class B {
    void listenToA(A a) {
        a.addPropertyChangeListener("Property1", doSomething);
        a.addPropertyChangeListener("Property2", doSomethingElse);
    }

    final PropertyChangeListener doSomething = evt -> {};
    final PropertyChangeListener doSomethingElse = evt -> {};
}

Answer 1

您可以按如下方式声明您的侦听器:

private final PropertyChangeListener myProperty1Listener = this::doSomething;
private final PropertyChangeListener myProperty2Listener = e -> doSomethingElse());

然后,您可以添加您的侦听器:

// using method reference
a.addPropertyChangeListener( "Property1", myProperty1Listener );
// using lambda expression
a.addPropertyChangeListener( "Property2", myProperty2Listener );

你可以删除它们:

a.removePropertyChangeListener( "Property1", myProperty1Listener );
a.removePropertyChangeListener( "Property2", myProperty2Listener );