Lambda 表达式

实例

1. 使用 Lambda 表达式对列表进行迭代

   // Java 8之前：
   List features = Arrays.asList("Lambdas", "Default Method", "Stream API", "Date and Time API");
   for (String feature : features) {
       System.out.println(feature);
   }
   
   // Java 8之后：
   List features = Arrays.asList("Lambdas", "Default Method", "Stream API", "Date and Time API");
   features.forEach(n -> System.out.println(n));
   
   // 使用Java 8的方法引用更方便，方法引用由::双冒号操作符标示，
   // 看起来像C++的作用域解析运算符
   features.forEach(System.out::println);
   

2. lambdas 实现 Runnable 接口

   // 1.1使用匿名内部类  
   new Thread(new Runnable() {  
       @Override  
       public void run() {  
           System.out.println("Hello world !");  
       }  
   }).start();  
   
   // 1.2使用 lambda expression  
   new Thread(() -> System.out.println("Hello world !")).start();  
   
   // 2.1使用匿名内部类  
   Runnable race1 = new Runnable() {  
       @Override  
       public void run() {  
           System.out.println("Hello world !");  
       }  
   };  
   
   // 2.2使用 lambda expression  
   Runnable race2 = () -> System.out.println("Hello world !");  
   
   // 直接调用 run 方法(没开新线程哦!)  
   race1.run();  
   race2.run();  
   

3. 使用 Lambda 表达式进行事件处理

   // Java 8之前：
   JButton show =  new JButton("Show");
   show.addActionListener(new ActionListener() {
       @Override
       public void actionPerformed(ActionEvent e) {
           System.out.println("Event handling without lambda expression is boring");
       }
   });
   
   // Java 8方式：
   show.addActionListener((e) -> {
       System.out.println("Light, Camera, Action !! Lambda expressions Rocks");
   });
   

4. 使用 Lambdas 排序集合

   String[] players = {"Rafael Nadal", "Novak Djokovic",   
       "Stanislas Wawrinka", "David Ferrer",  
       "Roger Federer", "Andy Murray",  
       "Tomas Berdych", "Juan Martin Del Potro",  
       "Richard Gasquet", "John Isner"};  
   
   // 1.1 使用匿名内部类根据 surname 排序 players  
   Arrays.sort(players, new Comparator() {  
       @Override  
       public int compare(String s1, String s2) {  
           return (s1.substring(s1.indexOf(" ")).compareTo(s2.substring(s2.indexOf(" "))));  
       }  
   });  
   
   // 1.2 使用 lambda expression 排序,根据 surname  
   Comparator sortBySurname = (String s1, String s2) ->   
       ( s1.substring(s1.indexOf(" ")).compareTo( s2.substring(s2.indexOf(" ")) ) );  
   Arrays.sort(players, sortBySurname);  
   
   // 1.3 或者这样,怀疑原作者是不是想错了,括号好多...  
   Arrays.sort(players, (String s1, String s2) ->   
       ( s1.substring(s1.indexOf(" ")).compareTo( s2.substring(s2.indexOf(" ")) ) )   
       );  
   
   // 2.1 使用匿名内部类根据 name lenght 排序 players  
   Arrays.sort(players, new Comparator() {  
       @Override  
       public int compare(String s1, String s2) {  
           return (s1.length() - s2.length());  
       }  
   });  
   
   // 2.2 使用 lambda expression 排序,根据 name lenght  
   Comparator sortByNameLenght = (String s1, String s2) -> (s1.length() - s2.length());  
   Arrays.sort(players, sortByNameLenght);  
   
   // 2.3 or this  
   Arrays.sort(players, (String s1, String s2) -> (s1.length() - s2.length()));  
   
   // 3.1 使用匿名内部类排序 players, 根据最后一个字母  
   Arrays.sort(players, new Comparator() {  
       @Override  
       public int compare(String s1, String s2) {  
           return (s1.charAt(s1.length() - 1) - s2.charAt(s2.length() - 1));  
       }  
   });  
   
   // 3.2 使用 lambda expression 排序,根据最后一个字母  
   Comparator sortByLastLetter =   
       (String s1, String s2) ->   
           (s1.charAt(s1.length() - 1) - s2.charAt(s2.length() - 1));  
   Arrays.sort(players, sortByLastLetter);  
   
   // 3.3 or this  
   Arrays.sort(players, (String s1, String s2) -> (s1.charAt(s1.length() - 1) - s2.charAt(s2.length() - 1)));