6. Lambda expressions

Lambda expressions

• Understanding Functional Interface is the key to learning Java8 Lambda expressions
• In order to avoid excessive definitions of anonymous inner classes, Lambda expressions are essentially the concept of functional programming.
• functional interface
  • Any interface that contains only one abstract method is a functional interface
  • For functional interfaces, we can create objects of the interface through lambda expressions

	package com;

/**
 * 推导Lambda表达式
 */
public class Lambda {
    // 3.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();


        // 4.局部内部类
        class Like3 implements ILike{
            @Override
            public void lambda() {
                System.out.println("i like lambda3");
            }
        }

        like = new Like3();
        like.lambda();

        // 5.匿名内部类 没有类的名称，必须借助接口或者弗列
        like = new ILike(){
            @Override
            public void lambda() {
                System.out.println("i like lambda4");
            }
        };
        like.lambda();

        // 6.用lambda简化
        like = ()->{
            System.out.println("i like lambda5");
        };
        like.lambda();
    }

}

// 1.定义一个函数式接口
interface ILike{
    void lambda();
}

// 2.实现类
class Like implements ILike{
    @Override
    public void lambda() {
        System.out.println("i like lambda");
    }
}

lambda expression: the premise is that it must be a functional interface

package com.lambda;

/**
 * 总结
 *      lambda表达式方法体中只能有一行代码的情况下才能简化为一行，如果有多行，那么就必须用{}代码块包裹
 *      前提是 接口为函数式接口
 *      多个参数也可以去掉参数类型，要去掉就都去掉，必须加上括号
 */
public class Lambda2 {
    public static void main(String[] args) {
        ILove love = null;

        // lambda表示简化
        love = (int a)-> {
            System.out.println("i love you " + a);
        };
        love.love(520);

        // 简化1.参数类型
        love = (a)-> {
            System.out.println("i love you " + a);
        };
        love.love(521);

        // 简化2.括号
        love = a -> {
            System.out.println("i love you " + a);
        };
        love.love(522);

        // 简化3.去掉花括号
        love = a -> System.out.println("i love you " + a);
        love.love(523);
    }

}

interface ILove{
    void love(int a);
}