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();
    }

}