java - java中的内部类和本地内部类有什么区别？

Question

如果一个类是本地内部类，这是否意味着它在另一个类的方法内部，或者它是否意味着它只是在某个地方的另一个方法中定义。

例如，在下面的代码中，MenuListener 是否被视为内部本地类？

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class MenuDemo extends JFrame{
private Container c;
private ImageIcon[] images = new ImageIcon[5];
private JLabel picture;
private JPanel mainPanel;
private JMenuBar menuBar;
private JMenu menu;
private JMenuItem bird,cat,dog,rabbit,pig;

public MenuDemo() {
    super("Menu Demo");

    c = getContentPane();
    c.setLayout(new BorderLayout());

    mainPanel = new JPanel();

    // Store the animal pictures in an array.
    for (int i=0; i<5; i++){
        images[i] = new ImageIcon("image" + i + ".gif");
    }
    //Set up the picture label.
    picture = new JLabel(images[0]);
    picture.setPreferredSize(new Dimension(177,122));
    mainPanel.add(picture, BorderLayout.CENTER);
    c.add(mainPanel);
    buildMenuBar();
    this.setJMenuBar(menuBar);
    pack();
    setVisible(true);
}

private void buildMenuBar(){
    MenuListener listener = new MenuListener();
    menuBar = new JMenuBar();

    menu = new JMenu("Animals");
    menu.setMnemonic(KeyEvent.VK_A);
    menuBar.add(menu);

    bird = new JMenuItem("Bird", KeyEvent.VK_B);
    bird.addActionListener(listener);
    menu.add(bird);

    cat = new JMenuItem("Cat", KeyEvent.VK_C);
    cat.addActionListener(listener);
    menu.add(cat);

    dog = new JMenuItem("Dog", KeyEvent.VK_D);
    dog.addActionListener(listener);
    menu.add(dog);

    rabbit = new JMenuItem("Rabbit", KeyEvent.VK_R);
    rabbit.addActionListener(listener);
    menu.add(rabbit);

    pig = new JMenuItem("Pig", KeyEvent.VK_P);
    pig.addActionListener(listener);
    menu.add(pig);
}

private class MenuListener implements ActionListener {
    public void actionPerformed(ActionEvent e){
        if (e.getSource() == bird)
            picture.setIcon(images[0]);
        else if (e.getSource() == cat)
            picture.setIcon(images[1]);
        else if (e.getSource() == dog)
            picture.setIcon(images[2]);
        else if (e.getSource() == rabbit)
            picture.setIcon(images[3]);
        if (e.getSource() == pig)
            picture.setIcon(images[4]);
    }
}

public static void main(String[] args){
    MenuDemo m = new MenuDemo();
    m.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}   
}

Answer 1

According to some official Oracle Java tutorial ，本地内部类是在代码块中定义的类，而不是另一个类定义的一部分。这意味着在方法或初始化程序 block 中定义的类。

根据该定义，MenuListener不是本地内部类——它只是一个内部类。

所以:

public class Outer {

    public class Inner1 {
    }

    public static class Inner2 {
    }

    public void method(){

        class LocalInner{
        }

        LocalInner yesThisActuallyCompiles = new LocalInner();
    }
}