lambda表达式推导和使用

lambda

• λ希腊字母表中排序第十一位的字母，英语名称为 Lambda，
• 避免匿名内部类定义过多
• 其实质属于函数式编程的概念

(params) -> expression
(params) -> statement
(params) -> { statements }

new Thread(()->System.out.println("多线程学习。。。")).start();

1、lambda表达式逐级推导

 package com.sxt.thread;

 /**
  * Lambda表达式 简化线程（用一次）的使用
  */
 public class LambdaThread {

     //静态内部类
     static class Test implements Runnable {
         public void run() {
             for (int i = 0; i < 20; i++) {
                 System.out.println("一边听歌");
             }
         }
     }

     public static void main(String[] args) {

         //new Thread(new Test()).start();

         //局部内部类
         class Test2 implements Runnable {
             public void run() {
                 for (int i = 0; i < 20; i++) {
                     System.out.println("一边听歌");
                 }
             }
         }

         new Thread(new Test2()).start();

         //匿名内部类 必须借助接口或是父类
         new Thread(new Runnable() {
             @Override
             public void run() {
                 for (int i = 0; i < 20; i++) {
                     System.out.println("一边听歌");
                 }
             }
         }).start();

         //jdk8简化
         new Thread(() -> {
             for (int i = 0; i < 20; i++) {
                 System.out.println("一边听歌");
             }
         }).start();
     }
 }

2、再次推导，加深印象

 package com.sxt.thread;

 /**
  * @ClassName LambdaTest01
  * @Description TODO
  * @Date 2019/7/23 22:46
  * @Version 1.0
  */
 public class LambdaTest01 {

     //静态内部类
     static class Like2 implements ILike{

         @Override
         public void lambda() {
             System.out.println("I Like Lambda2");
         }
     }

     public static void main(String[] args) {

         ILike like = new Like();
         like.lambda();

         like = new Like2();
         like.lambda();

         //方法内部类
         class Like3 implements ILike{

             @Override
             public void lambda() {
                 System.out.println("I Like Lambda3");
             }
         }
         like = new Like3();
         like.lambda();

         //匿名内部类
         like = new ILike() {
             @Override
             public void lambda() {
                 System.out.println("I Like Lambda4");
             }
         };
         like.lambda();
         //lambda推导必须存在类型
         like = () -> {
             System.out.println("I Like Lambda5");
         };
         like.lambda();
     }
 }

 interface ILike{
     void lambda();
 }

 //外部类
 class Like implements ILike{

     @Override
     public void lambda() {
         System.out.println("I Like Lambda");
     }
 }

3、lambda参数传递（无返回值）以及简化

 package com.sxt.thread;

 /**
  * lambda推导+参数
  */
 public class LambdaTest02 {

     public static void main(String[] args) {
         ILove love = (int a) -> {
             System.out.println("I Like Lambda-->" + a);
         };
         love.lambda(100);

         //简化
         love = (a) -> {
             System.out.println("I Like Lambda-->" + a);
         };
         love.lambda(60);

         //只有一个参数，（）可以省略
         love = a -> {
             System.out.println("I Like Lambda-->" + a);
         };
         love.lambda(80);

         //如果代码只是一行，还可以省略
         love = a -> System.out.println("I Like Lambda-->" + a);
         love.lambda(90);
     }
 }

 interface ILove {
     void lambda(int a);
 }

 //外部类
 class Love implements ILove {

     @Override
     public void lambda(int a) {
         System.out.println("I Like Lambda-->" + a);
     }
 }

4、多个参数+返回值

 package com.sxt.thread;

 /**
  * lambda推导+参数+返回值
  */
 public class LambdaTest03 {

     public static void main(String[] args) {
         IInterest interest = (int a, int c)-> {
             System.out.println("I Like Lambda-->" + (a + c));
             return a + c;
         };

         interest.lambda(100,200);

         interest = (a,c)-> {
             System.out.println("I Like Lambda-->" + (a + c));
             return a + c;
         };
         interest.lambda(200,200);

         //()不可以省略
         /*interest = a,c-> {
             System.out.println("I Like Lambda-->" + (a + c));
             return a + c;
         };*/

         interest = (a,c)-> {
             return a + c;
         };

         interest = (a,c)->a+c;

         interest = (a,c)->100;

         System.out.println(interest.lambda(10,20));

     }

 }

 interface IInterest {
     int lambda(int a, int b);
 }

 //外部类
 class Interest implements IInterest {

     @Override
     public int lambda(int a, int c) {
         System.out.println("I Like Lambda-->" + (a + c));
         return a + c;
     }
 }

5、多线程示例

 package com.sxt.thread;

 /**
  * lambda推导+参数+返回值
  */
 public class LambdaTest04 {

     public static void main(String[] args) {

         new Thread(()->{
             for (int i = 0; i <100 ; i++) {
                 System.out.println("123");
             }
         }).start();

         new Thread(()->System.out.println("456")).start();
     }

 }