java-lambda(笔记)

作用

1. 避免匿名内部类定义过多
2. 使代码简洁
3. 去掉了没有意义的代码，只留下核心

函数式接口

只包含一个抽象方法的函数式接口

对于函数式接口，可用lambda表达式

推导lambda表达式

1. 最早期版本（用了多态，父类引用指向子类对象，有继承的方法用子类的）

   package com.zihan.thread;
   
   /*
    推导lambda表达式
    */
   public class lambda {
       public static void main(String[] args) {
           ILike like = new like();
           like.lambda();
       }
   }
   
   //定义一个函数式接口
   interface ILike{
       void lambda();
   }
   //实现类
   class like implements ILike{
       public void lambda(){
           System.out.println("111222");
       }
   }
   

2. 优化之后用静态内部类

   注意static class这一块，下面属于类型转换，高转低

   package com.zihan.thread;
   
   /*
    推导lambda表达式
    */
   public class lambda {
       //3.静态内部类
       static class like2 implements ILike{
           public void lambda(){
               System.out.println("111222");
           }
       }
   
   
       public static void main(String[] args) {
           ILike like = new like();
           like.lambda();
           like = new like2();
           like.lambda();
       }
   }
   
   //定义一个函数式接口
   interface ILike{
       void lambda();
   }
   //实现类
   class like implements ILike{
       public void lambda(){
           System.out.println("111222");
       }
   }
   

3. main 方法里写局部内部类

   package com.zihan.thread;
   
   /*
    推导lambda表达式
    */
   public class lambda {
       //3.静态内部类
       static class like2 implements ILike{
           public void lambda(){
               System.out.println("111222");
           }
       }
   
   
       public static void main(String[] args) {
           ILike like = new like();
           like.lambda();
           like = new like2();
           like.lambda();
           //4.局部内部类
           class like3 implements ILike{
               public void lambda(){
                   System.out.println("111222");
               }
           }
           like = new like3();
           like.lambda();
       }
   
   
   
   }
   
   //定义一个函数式接口
   interface ILike{
       void lambda();
   }
   //实现类
   class like implements ILike{
       public void lambda(){
           System.out.println("111222");
       }
   }
   

4. 用了匿名内部类

   package com.zihan.thread;
   
   /*
    推导lambda表达式
    */
   public class lambda {
       //3.静态内部类
       static class like2 implements ILike{
           public void lambda(){
               System.out.println("111222");
           }
       }
   
   
       public static void main(String[] args) {
           ILike like = new like();
           like.lambda();
           like = new like2();
           like.lambda();
           //4.局部内部类
           class like3 implements ILike{
               public void lambda(){
                   System.out.println("111222");
               }
           }
           like = new like3();
           like.lambda();
   
           //5.匿名内部类
           like = new ILike() {
               @Override
               public void lambda() {
                   System.out.println("111222");
               }
           };
           like.lambda();
       }
   
   
   
   }
   
   //定义一个函数式接口
   interface ILike{
       void lambda();
   }
   //实现类
   class like implements ILike{
       public void lambda(){
           System.out.println("111222");
       }
   }
   

5. 用lambda解决

   package com.zihan.thread;
   
   /*
    推导lambda表达式
    */
   public class lambda {
       //3.静态内部类
       static class like2 implements ILike{
           public void lambda(){
               System.out.println("111222");
           }
       }
   
   
       public static void main(String[] args) {
           ILike like = new like();
           like.lambda();
           like = new like2();
           like.lambda();
           //4.局部内部类
           class like3 implements ILike{
               public void lambda(){
                   System.out.println("111222");
               }
           }
           like = new like3();
           like.lambda();
   
           //5.匿名内部类
           like = new ILike() {
               @Override
               public void lambda() {
                   System.out.println("111222");
               }
           };
           like.lambda();
           //6. 用lambda简化
           like = ()->{
               System.out.println("111222");
           };
           like.lambda();
       }
   
   
   
   }
   
   //定义一个函数式接口
   interface ILike{
       void lambda();
   }
   //实现类
   class like implements ILike{
       public void lambda(){
           System.out.println("111222");
       }
   }
   

   静态内部类要放在psvm外面，其余内部类放在psvm中，因为static在主方法之前

6. 带参数的例子

   package com.zihan.thread;
   
   public class Lambda2 {
       static class Love implements Ilove {
           @Override
           public void love(int a) {
               System.out.println("i love " + a);
           }
       }
   
       public static void main(String[] args) {
   
   
           Ilove love = (int a) -> {
               System.out.println("i love " + a);
           };
           love.love(3);
   
           //简化一，去参数类型
           love = ( a) -> {
               System.out.println("i love " + a);
           };
           love.love(4);
           //简化二，去参数括号
           love = a -> {
               System.out.println("i love " + a);
           };
           love.love(5);
           //简化三，取代码体花括号
           love = a -> System.out.println("i love " + a);;
           love.love(521);
       }
   }