Java 8 Lambda 表达式 - 嵌套类中的多个方法怎么样

Question

我正在阅读有关新功能的信息:http://www.javaworld.com/article/2078836/java-se/love-and-hate-for-java-8.html

我看到了下面的例子:

使用匿名类:

button.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent ae) {
        System.out.println("Action Detected");
    }
});

使用 Lambda:

button.addActionListener(e -> {
    System.out.println("Action Detected");
});

如果有人想在匿名类中实现多个方法，他们会用 MouseListener 做什么，例如:

public void mousePressed(MouseEvent e) {
    saySomething("Mouse pressed; # of clicks: "
               + e.getClickCount(), e);
}

public void mouseReleased(MouseEvent e) {
    saySomething("Mouse released; # of clicks: "
               + e.getClickCount(), e);
}

...等等？

Answer 1

来自 JLS 9.8

A functional interface is an interface that has just one abstract method, and thus represents a single function contract.

Lambda 需要这些功能接口(interface)，因此仅限于它们的单一方法。实现多方法接口(interface)仍然需要使用匿名接口(interface)。

addMouseListener(new MouseAdapter() {

    @Override
    public void mouseReleased(MouseEvent e) {
       ...
    }

    @Override
    public void mousePressed(MouseEvent e) {
      ...
    }
});