lambda expression format

Lambda expressions

Lambda is an anonymous function, we can put Lambda expressions it can be understood as a piece of code passed (pass code that will be the same as the data). You can write simpler, more flexible code. As a more compact code style, the Java language skills has improved.

Lambda expressions left: Lambda expressions argument list;
right Lambda expressions: Function Lambda expressions need to be performed, i.e. Lambda body;

Lambda expression syntax

• A syntax: no parameters, no return value

public void test1(){
    int num = 0; //匿名函数用成员变量，jdk1.7前，必须final修饰

    Runnable r = new Runnable() {
        @Override
        public void run() {
            System.out.println("Hello World!" + num);
        }
    };
    r.run();

    //Lambda表达式写法
    Runnable r1 = () -> System.out.println("Hello Lambda!");
    r1.run();
}

• Two syntax: There is a parameter, and no return value

public void test2(){
    //Consumer 消费型接口 属于Java8 内置的四大核心函数式接口之一
    //若只有一个参数，小括号可以省略不写
    //Consumer<String> con = (x) -> System.out.println(x);
   Consumer<String> con = x -> System.out.println(x);
   con.accept("武汉加油！");
}

• Three syntax: two or more parameters, return values, and more than one statement Lambda body

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

• Syntax four: Lambda body if only one statement, return and curly braces can be omitted

public void test4(){
    Comparator<Integer> com = (x, y) -> Integer.compare(x, y);
}

• Syntax five: data type parameter list of Lambda expressions can be omitted, because the JVM compiler infer from the context, data types, namely "type inference"

public void test5(){
    //String[] strs;
    //strs = {"aaa", "bbb", "ccc"};

    List<String> list = new ArrayList<>();
    show(new HashMap<>());
}

public void show(Map<String, Integer> map){

}

Two, Lambda expressions need to support "function interface" of the
function interface: The interface is only one interface abstract method, called functional interface. You can use annotations @FunctionalInterface modification, you can check whether the function interface

@FunctionalInterface //函数式接口的注解
public interface MyFun {
	public Integer getValue(Integer num);
}

//对一个数进行运算
@Test
public void test6(){
    System.out.println(operation(100, (x) -> x * x));
    System.out.println(operation(200, (y) -> y + 200));
}