1.内部类

1 package innerClass; 2  3 import java.awt.*; 4 import java.awt.event.*; 5 import java.util.*; 6 import javax.swing.*; 7 import javax.swing.Timer; 8  9 /**10  * This program demonstrates the use of inner classes.11  * @version 1.11 2015-05-1212  * @author Cay Horstmann13  */14 public class InnerClassTest15 {16    public static void main(String[] args)17    {18       TalkingClock clock = new TalkingClock(1000, true);19       clock.start();20 21       // keep program running until user selects "Ok"22       JOptionPane.showMessageDialog(null, "Quit program?");23       System.exit(0);24    }25 }26 27 /**28  * A clock that prints the time in regular intervals.29  */30 class TalkingClock31 {32    private int interval;33    private boolean beep;34 35    /**36     * Constructs a talking clock37     * @param interval the interval between messages (in milliseconds)38     * @param beep true if the clock should beep39     */40    public TalkingClock(int interval, boolean beep)41    {42       this.interval = interval;43       this.beep = beep;44    }45 46    /**47     * Starts the clock.48     */49    public void start()50    {51       ActionListener listener = new TimePrinter();52       Timer t = new Timer(interval, listener);53       t.start();54    }55 56    public class TimePrinter implements ActionListener57    {58       public void actionPerformed(ActionEvent event)59       {60          System.out.println("At the tone, the time is " + new Date());61          if (beep) Toolkit.getDefaultToolkit().beep();62       }63    }64 }

2.匿名内部类

1 package anonymousInnerClass; 2  3 import java.awt.*; 4 import java.awt.event.*; 5 import java.util.*; 6 import javax.swing.*; 7 import javax.swing.Timer; 8  9 /**10  * This program demonstrates anonymous inner classes.11  * @version 1.11 2015-05-1212  * @author Cay Horstmann13  */14 public class AnonymousInnerClassTest15 {16    public static void main(String[] args)17    {18       TalkingClock clock = new TalkingClock();19       clock.start(1000, true);20 21       // keep program running until user selects "Ok"22       JOptionPane.showMessageDialog(null, "Quit program?");23       System.exit(0);24    }25 }26 27 /**28  * A clock that prints the time in regular intervals.29  */30 class TalkingClock31 {32    /**33     * Starts the clock.34     * @param interval the interval between messages (in milliseconds)35     * @param beep true if the clock should beep36     */37    public void start(int interval, boolean beep)38    {39       ActionListener listener = new ActionListener()40          {41             public void actionPerformed(ActionEvent event)42             {43                System.out.println("At the tone, the time is " + new Date());44                if (beep) Toolkit.getDefaultToolkit().beep();45             }46          };47       Timer t = new Timer(interval, listener);48       t.start();49    }50 }

第二种方法比第一种更为简洁，多年来，Java程序员习惯的做法是用匿名内部类实现事件监听器和其他回调。

上述两种方法可以用lambda来实现，更为简洁

1 public void start(int interval, boolean beep) {2         Timer t = new Timer(interval, event -> {3             System.out.println("At the tone, the time is " + new Date());4             if (beep) Toolkit.getDefaultToolkit().beep();5         });6         t.start();7 }

3.匿名内部类的一个使用技巧--“双括号初始化”

假设你想构造一个数组列表，并将它传递到一个方法：

1 ArrayList
     
       friends = new ArrayList<>();2 friends.add("Harry");3 friends.add("Tony");4 invite(friends);
     

如果不在需要这个数组列表，最好让他作为一个匿名列表，方法如下：

invite(new ArrayList
     
      () {
   { add("Harrry"); add("Tony"); }});
     

外层括号建立了ArrayList的一个匿名子类，内层括号则是一个对象构造块。

 4.静态内部类

1 package staticInnerClass; 2  3 /** 4  * This program demonstrates the use of static inner classes. 5  * @version 1.02 2015-05-12 6  * @author Cay Horstmann 7  */ 8 public class StaticInnerClassTest 9 {10    public static void main(String[] args)11    {12       double[] d = new double[20];13       for (int i = 0; i < d.length; i++)14          d[i] = 100 * Math.random();15       ArrayAlg.Pair p = ArrayAlg.minmax(d);16       System.out.println("min = " + p.getFirst());17       System.out.println("max = " + p.getSecond());18    }19 }20 21 class ArrayAlg22 {23    /**24     * A pair of floating-point numbers25     */26    public static class Pair27    {28       private double first;29       private double second;30 31       /**32        * Constructs a pair from two floating-point numbers33        * @param f the first number34        * @param s the second number35        */36       public Pair(double f, double s)37       {38          first = f;39          second = s;40       }41 42       /**43        * Returns the first number of the pair44        * @return the first number45        */46       public double getFirst()47       {48          return first;49       }50 51       /**52        * Returns the second number of the pair53        * @return the second number54        */55       public double getSecond()56       {57          return second;58       }59    }60 61    /**62     * Computes both the minimum and the maximum of an array63     * @param values an array of floating-point numbers64     * @return a pair whose first element is the minimum and whose second element65     * is the maximum66     */67    public static Pair minmax(double[] values)68    {69       double min = Double.POSITIVE_INFINITY;70       double max = Double.NEGATIVE_INFINITY;71       for (double v : values)72       {73          if (min > v) min = v;74          if (max < v) max = v;75       }76       return new Pair(min, max);77    }78 }

优点：1.避免编写两个函数，一个计算最小值，一个计算最大值，只需要遍历一次就可以了。

 　　  2.Pair是一个十分大众化的名字，其他程序员很有可能会使用这个名字，这样就会产生名字冲突，解决这个问题的办法是将Pair定义为ArrayAlg的内部公有类，通过ArrayAlg.Pair来访问它。