Java 8 Lambda表达式 - 嵌套类中的多个方法怎么样 [英] Java 8 Lambda Expressions - what about multiple methods in nested class

问题描述

我正在阅读以下新功能： http://www.javaworld.com/article/2078836/java-se/love-and-hate-for-java-8.html

I'm reading about the new features at: http://www.javaworld.com/article/2078836/java-se/love-and-hate-for-java-8.html

我看到了以下示例：

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 MouseListener ，有人会怎么做他们想在匿名类中实现多个方法，例如：

What would someone do with a MouseListener if they wanted to implement multiple methods within the anonymous class, e.g.:

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);
}

......依此类推？

... and so on?

推荐答案

来自JLS 9.8

功能界面是一个界面只有一个抽象方法，因此
表示单个函数契约。

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

Lambdas需要这些功能接口因此受到限制他们的单一方法。匿名接口仍然需要用于实现多方法接口。

Lambdas require these functional interfaces so are restricted to their single method. Anonymous interfaces still need to be used for implementing multi-method interfaces.

addMouseListener(new MouseAdapter() {

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

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

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