lamda表達式

Lambda 表達式的簡單例子:
// 1. 不需要參數,返回值爲 5
() -> 5

// 2. 接收一個參數(數字類型),返回其2倍的值
x -> 2 * x

// 3. 接受2個參數(數字),並返回他們的差值
(x, y) -> x – y

// 4. 接收2個int型整數,返回他們的和
(int x, int y) -> x + y

// 5. 接受一個 string 對象,並在控制檯打印,不返回任何值(看起來像是返回void)
(String s) -> System.out.print(s)

public class Java8Tester {
   public static void main(String args[]){
      Java8Tester tester = new Java8Tester();
        
      // 類型聲明
      MathOperation addition = (int a, int b) -> a + b;
        
      // 不用類型聲明
      MathOperation subtraction = (a, b) -> a - b;
        
      // 大括號中的返回語句
      MathOperation multiplication = (int a, int b) -> { return a * b; };
        
      // 沒有大括號及返回語句
      MathOperation division = (int a, int b) -> a / b;
        
      System.out.println("10 + 5 = " + tester.operate(10, 5, addition));
      System.out.println("10 - 5 = " + tester.operate(10, 5, subtraction));
      System.out.println("10 x 5 = " + tester.operate(10, 5, multiplication));
      System.out.println("10 / 5 = " + tester.operate(10, 5, division));
        
      // 不用括號
      GreetingService greetService1 = message ->
      System.out.println("Hello " + message);
        
      // 用括號
      GreetingService greetService2 = (message) ->
      System.out.println("Hello " + message);
        
      greetService1.sayMessage("Runoob");
      greetService2.sayMessage("Google");
   }
    
   interface MathOperation {
      int operation(int a, int b);
   }
    
   interface GreetingService {
      void sayMessage(String message);
   }
    
   private int operate(int a, int b, MathOperation mathOperation){
      return mathOperation.operation(a, b);
   }
}

輸出結果爲:

$ javac Java8Tester.java 
$ java Java8Tester
10 + 5 = 15
10 - 5 = 5
10 x 5 = 50
10 / 5 = 2
Hello Runoob
Hello Google