JAVA in -> Lambda function

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-> is Lambda expressions, also known as Lambda function, the new features of Java 8.

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Lambda can be read as "wave motor."
Lambda allowed to function as an argument of a method (function as a parameter passed into the process).
Lambda expressions can make use of the code becomes more simple and compact.

The basic syntax Lambda expressions:

(parameters) -> expression
或
(parameters) ->{ statements; }

The following are important characteristics of a lambda expression:

Optional type declaration: do not need to declare the parameter type, the compiler can be unified identification parameter value.
The optional parameters in parentheses: no need to define a parameter in parentheses, but a number of parameters need to be defined parentheses.
Optional braces: if the body contains a statement, you do not need to use braces.
Optional return keyword: If the subject is only one expression that returns a value, the compiler will automatically return value, braces need to specify clear expression that returns a value

Lambda expressions Examples of
simple example Lambda expressions:
a:

    // 1. 不需要参数,返回值为 5  
    () -> 5  
      
    // 2. 接收一个参数(数字类型),返回其2倍的值  
    x -> 2 * x  
      
    // 3. 接受2个参数(数字),并返回他们的差值  
    (x, y) -> x – y  
      
    // 4. 接收2个int型整数,返回他们的和  
    (int x, int y) -> x + y  
      
    // 5. 接受一个 string 对象,并在控制台打印,不返回任何值(看起来像是返回void)  
    (String s) -> System.out.print(s)

two:

String[] days = {" Monday", "Tuesday",  
       "Wednesday", "Thursday",
       "Friday",  "Saturday",    
       "Sunday"};  
List<String> allDays =  Arrays.asList(days);  
  
// 以前的循环方式  
for (String allDay : allDays) {  
     System.out.print(allDay + "; ");  
}  
  
// 使用 lambda 表达式以及函数操作(functional operation)  
allDays.forEach((allDay) -> System.out.print(allDay + "; "));  
   
// 在 Java 8 中使用双冒号操作符(double colon operator)  
allDays.forEach(System.out::println);

These three are the same output

We usually write for loop, use a lambda expression form will be different, but the result is the same. The code looks a little on the high force grid.

//双冒号运算操作符是类方法的句柄，lambda表达式的一种简写  
方法调用
person -> person.getAge();
可以替换成
Person::getAge

x -> System.out.println(x)
可以替换成
System.out::println

Lambda function briefly summarize the advantages and disadvantages
advantages: simplicity, reduce code redundancy
Disadvantages: difficult to understand, difficult to debug

With more words, you get used to it.