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This article shows you what is the use of Lambda expression in Java. The content is concise and easy to understand. It will definitely brighten your eyes. I hope you can get something through the detailed introduction of this article.

Lambda

Lambda is an anonymous function, and we can think of a lambda expression as a piece of code that can be passed.

Lambda succinctly passes code or methods as parameters for execution.

The core of functional programming is to take the function as a value.

Functional interface: an interface with only one abstract method is called a functional interface. Functional interfaces can be annotated with @ FunctionalInterface.

The lambda expression is split into two parts

Left: parameter list for lambda expression

Right: the function to be performed in the lambda expression, that is, the lambda body

Syntax format 1: no parameter, no return value @ Testpublic void test () {/ / ()-> System.out.println ("Hello"); Runnable a = new Runnable () {@ Override public void run () {System.out.println ("Hello")}}; / / equivalent to Runnable A1 = ()-> System.out.println ("Hello"); a1.run () Syntax format 2: there is one parameter, no return value (if only one parameter parenthesis can be omitted) @ Testpublic void test () {/ / Consumer annotated interface (functional interface) unique abstract method void accept (T t); / / left parameter-> right executor Consumer con = (x)-> System.out.println (x) / / x-> System.out.println (x); con.accept ("h");} syntax format 3: there are more than two parameters, and there are multiple statements in the lambda body (if there is only one statement in the lambda body, return and curly braces can be omitted) @ Testpublic void test () {/ / Comparator is annotated @ FunctionalInterface interface for example abstract method int compare (To1TO2) Comparator com = (xQuery y)-> {System.out.println ("h0"); return (x

< y) ? -1 : ((x == y) ? 0 : 1); }; com.compare(1,2);} 注意：lambda表达式的参数类型可以省略不写，因为jvm编译器可以从上下文推断出数据类型。即"类型推断"如果要在参数里面写数据类型，都要写上。 实例实例1：class Employee { private String name; private int age; private double salary; //省略 get and set and constructor}interface MyPredicate { boolean test(T t);}public class Test{ static List list = Arrays.asList( new Employee("张三",10,1), new Employee("里斯",20,1), new Employee("王五",16,1), new Employee("二三",30,1) ); public static List filterEmployee(List list,MyPredicate mp){ List emps = new ArrayList(); for (Employee employee : list) { if(mp.test(employee)){ emps.add(employee); } } return emps; } @org.junit.Test public void test1(){ //需要使用自定义的方法 List list2 = filterEmployee(list,(e) ->

E.getAge () > = 15); list2.stream () .map (Employee::getName) .forEach (System.out::println);} @ org.junit.Test public void test2 () {/ / you can use stream to filter list collections without using the custom interface List list2 = list.stream (). Filter ((e)-> e.getAge () > = 15) .filtering (Collectors.toList ()) List2.stream () .map (Employee::getName) .forEach (System.out::println);}} instance 2:

Create a MyFun interface with @ FunctionalInterface annotations and create an abstract method Integer getValue (Integer num); do something on the variables in the Test class.

@ FunctionalInterfaceinterface MyFun {Integer getValue (Integer num);} public class Test {@ org.junit.Test public void Test () {operation (100Magnenum-> + num);} / * * param1 num: the number of integers passed in * param2 mf: to manipulate the integer in a certain way. * * / public Integer operation (Integer num,MyFun mf) {return mf.getValue (num);}} class Employee {private String name; private int age; private double salary; @ Override public String toString () {return "[" + this.name+ "," + this.getAge () + "," + this.getSalary () + "]" } / / omit getter and setter and constructor} public class Test {List list = Arrays.asList (new com.bilibili.lambda.test1.Employee ("Zhang San", 10jue 1), new com.bilibili.lambda.test1.Employee ("Reese", 20pr 1), new com.bilibili.lambda.test1.Employee ("Wang Wu", 16jue 1), new Employee ("Er3", 30jin1) @ org.junit.Test public void test () {Collections.sort (list, (E1 Magee e2)-> {if (e1.getAge () = = e2.getAge ()) {return e1.getName () .compareTo (e2.getName ());} else {/ / compare age return Integer.compare (e1.getAge (), e2.getAge ()) For (Employee e: list) {System.out.println (e);} four core functional interfaces

Consumer: consumer interface void accept (T t)

Supplier: co-get interface T ()

Function: functional interface T represents the parameter, and R represents the return value R apply (T t)

Predicate: assertive interface boolean test (T t)

Class Test {@ org.junit.Test publilc void test () {happy (10000, (money)-> System.out.println ("happy consumption" + money+ "yuan");} public void happy (double money,Consumer con) {con.accept (money);}} lambda method reference

Method reference: if the inner method in the lambda body has been implemented, we can use "method reference"

(it can be understood as another form of lambda when a method is referenced)

There are three main grammatical formats:

Object:: instance method name

Class:: static method name

Class:: instance method name

Class Test {/ / object: instance method name @ org.junit.Test public void test () {Consumer con = (x)-> System.out.println (x); con.accept (""); Consumer con2 = System.out::println; con2.accept ("") } / / Class: static method name @ org.junit.Test public void test2 () {Comparator com = (XMague y)-> Integer.compare (XMague y); Comparator com2 = Integer::compare; com.compare (1Magi 2); com2.compare (1Mague 2) } / / Class: instance method name @ org.junit.Test () {BiPredicate bp = (xPowery)-> x.equals (y); bp.test ("a", "a"); BiPredicate bp2 = String::equals;}} lambda constructor reference

Format:

CalssName::new

Class Test {@ org.junit.Test public void test () {Supplier sup = ()-> new String (); / / the constructor reference here depends on the number of parameters of the interface method. Here the functional interface T get (); is a no-parameter abstract method, so String is also an instantiated no-parameter constructor when instantiating other classes are also applicable to Supplier sup2 = String::new; String str = sup2.get ();}} the above is what is the use of Lambda expression in Java, have you learned any knowledge or skills? If you want to learn more skills or enrich your knowledge reserve, you are welcome to follow the industry information channel.

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