java8新特性-lambda表达式和stream API的简单使用

今天药忘吃喽~ 2021-12-16 09:11 213阅读 0赞

## 一、为什么使用lambda ##

Lambda 是一个 匿名函数，我们可以把 Lambda表达式理解为是 一段可以传递的代码（将代码像数据一样进行传递）。可以写出更简洁、更灵活的代码。作为一种更紧凑的代码风格，使Java的语言表达能力得到了提升。

package com.duchong.java8;
    
    /**
     * @author DUCHONG
     * @since 2019-01-02 15:00
     **/
    public class LambdaTest2 {
    
        public static void main(String[] args) {
    
            //原写法
            new Thread(new Runnable() {
                @Override
                public void run() {
                    System.out.println("run ----hello lambda");
                }
            }).start();
            //lambda表达式写法
            new Thread(()-> System.out.println("run2 ----hello lambda")).start();
        }
    }

![849431-20190102151808692-206935713.png][]

## 二、lambda语法 ##

Lambda 表达式在Java 语言中引入了一个新的语法元素和操作符。这个操作符为 "**->**"， 该操作符被称为 Lambda 操作符或剪头操作符。它将 Lambda 分为两个部分：

*  左侧：指定了 Lambda 表达式需要的所有参数
 *  右侧：指定了 Lambda 体，即 Lambda 表达式要执行的功能。

![849431-20190102152259566-266478792.png][]

![849431-20190102152309649-1753297844.png][]

## 三、引用 ##

### 3.1、方法引用 ###

![849431-20190102152703657-1473285003.png][]

![849431-20190102152712363-1554798381.png][]

![849431-20190102152722112-1127619905.png][]

### 3.2、构造器引用 ###

![849431-20190102152834439-301847195.png][]

### 3.3、数组引用 ###

![849431-20190102152855935-1397629983.png][]

## 四、stream API简单使用 ##

包名：java.util.stream .\*

需求：查询出集合中薪水大于5000 的员工。

Employee.java

package com.duchong.java8;
    
    public class Employee {
    
        private String name;
        private int age;
        private char gender;
        private double salary;
    
        public Employee() {
        }
    
        public Employee(String name, int age, char gender, double salary) {
            this.name = name;
            this.age = age;
            this.gender = gender;
            this.salary = salary;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public int getAge() {
            return age;
        }
    
        public void setAge(int age) {
            this.age = age;
        }
    
        public char getGender() {
            return gender;
        }
    
        public void setGender(char gender) {
            this.gender = gender;
        }
    
        public double getSalary() {
            return salary;
        }
    
        public void setSalary(double salary) {
            this.salary = salary;
        }
    
        @Override
        public String toString() {
            return "Employee [name=" + name + ", age=" + age + ", gender=" + gender
                    + ", salary=" + salary + "]";
        }
    
    }

main

package com.duchong.java8;
    
    import java.util.Arrays;
    import java.util.List;
    import java.util.stream.Collectors;
    
    /**
     * @author DUCHONG
     * @since 2019-01-02 15:00
     **/
    public class LambdaTest2 {
    
        public static void main(String[] args) {
    
    
            List<Employee> employees = Arrays.asList(
                    new Employee("duchong", 18, '男', 0),
                    new Employee("duchong", 17, '男', 0),
                    new Employee("duchong1", 20, '女', 5000),
                    new Employee("duchong2", 18, '女', 8000),
                    new Employee("duchong3", 22, '男', 9000),
                    new Employee("duchong4", 30, '男', 11000)
            );
    
    
            //过滤大于5000
            employees.stream()
                    .filter((e) -> e.getSalary() >= 5000)
                    .forEach(System.out::println);
    
            System.out.println("---------------------------------------");
            //获取名称 不去重
            employees.stream()
                    .map(Employee::getName)
                    .forEach(System.out::println);
            //获取名称 去重
            System.out.println("---------------------------------------");
            employees.stream()
                    .map(Employee::getName)
                    .distinct()
                    .forEach(System.out::println);
    
            //获取唯一性的Name列表
            List<String> employeeList=employees.stream()
                                                .map(Employee::getName)
                                                .distinct()
                                                .collect(Collectors.toList());
        }
    }

结果：

![849431-20190102153455991-1114710139.png][]

转载于:https://www.cnblogs.com/geekdc/p/10208877.html

[849431-20190102151808692-206935713.png]: /images/20211214/f103c296dfb2426abba7b32870ba6123.png
[849431-20190102152259566-266478792.png]: /images/20211214/5b79659b93e0439aa2ee82f9aa6244c3.png
[849431-20190102152309649-1753297844.png]: /images/20211214/c84c2395ed534946b9dab1dd54ab2c10.png
[849431-20190102152703657-1473285003.png]: /images/20211214/7824159e3f2d413eaad799ba28f5610b.png
[849431-20190102152712363-1554798381.png]: /images/20211214/29a0da7559494516b632f2f66aad5512.png
[849431-20190102152722112-1127619905.png]: /images/20211214/1969c06cdf63499da09631afd66f572f.png
[849431-20190102152834439-301847195.png]: /images/20211214/94e95d522e1d4a989049a656d6ffbcbe.png
[849431-20190102152855935-1397629983.png]: /images/20211214/9d7cc1887b844c8eb3117ea1891c8ccf.png
[849431-20190102153455991-1114710139.png]: /images/20211214/0065762d4e6c4992a47f8de7dd136c06.png