Java8 Lambda expression of the new features (b)

Lambda expression syntax basis: introducing a new one operator (referred to as arrow operator or operator Lambda): "->" the operator of the expression is split into two parts: the left: Lambda expressions parameter list right: Lambda required in the operation of the functions performed

1. 语法格式一：无参数，无返回值
               () -> System.out.println("Hello Lambda!");

2. 语法格式二：有一个参数，无返回值（参数可不加括号）
               (x) -> System.out.println(x); 或者 x -> System.out.println(x);

3. 语法格式三：有两个以上的参数，且Lambda体重有多条语句；有两个以上的参数，且Lambda体重有一条语句，大括号和return都可省略
               Comparator<Integer> com = (x, y) -> {
                   System.out.println("函数式接口");
                   return Integer.compare(x, y);
               };
   
               Comparator<Integer> com = (x, y) ->  Integer.compare(x, y);

4. 语法格式四：Lambda表达式中的参数列表的类型可以不用说明，jvm编译器会通过上下文进行推断出数据类型，即“类型推断”

package lambda;

import org.junit.Test;

import java.util.Comparator;
import java.util.function.Consumer;

public class TestLambda2 {

    @Test
    public void test1() {
        Runnable r = () -> System.out.println("Hello Lambda!");
        r.run();
    }

    @Test
    public void test2() {
        Consumer c = x -> System.out.println(x);
        c.accept("清风徐来");
    }

    @Test
    public void test3() {
        Comparator<Integer> com = (x, y) -> {
            System.out.println("函数式接口");
            return Integer.compare(x, y);
        };
//        Comparator<Integer> com = (x, y) ->  Integer.compare(x, y);
    }

    @Test
    public void test4() {
        Integer num = operation(100, (x) -> x * x);
        System.out.println(num);
    }

    //对一个数进行运算
    public Integer operation(Integer num, MyFun mf) {
        return mf.getValue(num);
    }
}

MyFun的定义参考前一节：https://blog.csdn.net/qq_38358499/article/details/104636487
注意：lambda需要“函数式接口”的支持，
      函数式接口：接口中只有一个抽象方法的接口，称为函数式接口。可以使用注解修饰：@FunctionalInterface，来检查是否是函数式接口