使用参数在对象上调用非静态方法引用

Question

我正在创建一个事件处理框架并希望执行以下操作：

// E: event listener interface, T: event class
class EventManager<E, T> {

    ArrayList<E> listeners = new ArrayList<E>();

    // `method` is some sort of reference to the method to call on each listener. There is no `MethodReference` type, I just put it there as I'm not sure what type should be in its place
    protected void notifyListeners(MethodReference method, T eventObj) {
        for (E listener : listeners) // call `method` from `listener` with `eventObj` as an argument
   }
}

class SpecialisedEventManager extends EventManager<SomeListener, SomeEvent> {

    // Some method that would want to notify the listeners
    public void foo() {
        ...
        // I would like onEvent() to be called from each listener with new SomeEvent() as the argument
        notifyListeners(SomeListener::onEvent, new SomeEvent());
        ...
    }

    // Some other method that would want to notify the listeners
    public void bar() {
        ...
        notifyListeners(SomeListener::onOtherEvent, new SomeEvent());
        ...
    }

}

interface SomeListener {
    public void onEvent(SomeEvent event);
    public void onOtherEvent(SomeEvent event);
}

但我不确定如何引用 onEvent() 和 onOtherEvent() 方法，以便使用适当的参数从每个侦听器对象调用它们。有什么想法吗？

Answer 1

方法引用只是实现功能接口的一种方式，因此您必须自己定义一个合适的接口或search the predefined types 进行匹配。

由于您的侦听器方法使用目标侦听器实例和事件对象，并且 return 没有值，因此 BiConsumer 是合适的类型：

protected void notifyListeners(BiConsumer<E,T> method, T eventObj) {
    for(E listener: listeners)
        method.accept(listener, eventObj);
}

方法引用 SomeListener::onEvent 和 SomeListener::onOtherEvent 具有 “Reference to an instance method of an arbitrary object” 的形式，其中调用者提供目标实例来调用方法，类似于 lambda 表达式 (l,e) -> l.onEvent(e) (l,e) -> l.onOtherEvent(e)，这就是目标实例成为第一个功能参数的原因。

使用参数在对象上调用非静态方法引用

Calling non-static method reference on an object with an argument

java

events

event-handling

java-8