Java8函数式编程例子

灰太狼 2022-04-24 08:46 202阅读 0赞

### 创建pojo ###

public class UserDemo {
    
        private String id;
    
        private String name;
    
        private Integer age;
    
        // 自行补充get/set方法
    }

### 例子 ###

package com.wu.parker.common.demo.util;
    
    import java.util.ArrayList;
    import java.util.Collections;
    import java.util.Comparator;
    import java.util.List;
    import java.util.stream.Collectors;
    
    /**
     * 函数式编程例子
     * @author wusq
     * @date 2019/4/20
     */
    public class StreamMain {
    
        static List<UserDemo> userDemoList;
    
        /**
         * 初始化集合
         */
        static void init(){
    
            userDemoList = new ArrayList<>();
    
            UserDemo a = new UserDemo();
            a.setId("a");
            a.setName("user-a");
            a.setAge(28);
            userDemoList.add(a);
    
            UserDemo b = new UserDemo();
            b.setId("b");
            b.setName("user-b");
            b.setAge(18);
            userDemoList.add(b);
    
            UserDemo c = new UserDemo();
            c.setId("c");
            c.setName("user-c");
            c.setAge(38);
            userDemoList.add(c);
    
        }
    
        /**
         * 过滤年龄小于20的数据
         */
        static void filter(){
            userDemoList = userDemoList.stream().filter(o -> o.getAge() < 20).collect(Collectors.toList());
        }
    
        /**
         * 获取id的List
         */
        static void getIdList(){
            List<String> list = userDemoList.stream().map(UserDemo::getId).collect(Collectors.toList());
            list.forEach(o -> System.out.println(o));
        }
    
        /**
         * 拼接ID
         */
        static void joinId(){
    
            String ids = userDemoList.stream().map(UserDemo::getId).collect(Collectors.joining(","));
            System.out.println(ids); // 输出a,b,c
    
            // 加上前后缀
            ids = userDemoList.stream().map(UserDemo::getId).collect(
                    Collectors.joining(",", "prifix-", "-suffix"));
            System.out.println(ids); // 输出prifix-a,b,c-suffix
    
        }
    
        /**
         * 年龄排序
         */
        static void sort(){
            Collections.sort(userDemoList, Comparator.comparing(UserDemo::getAge));
        }
    
        /**
         * 年龄求和
         */
        static void sum(){
            int amout = userDemoList.stream().map(UserDemo::getAge).reduce(Integer::sum).get();
            System.out.println(amout);
        }
    
        /**
         * 打印
         */
        static void print(){
            userDemoList.forEach(o -> System.out.println(o.getId() + o.getName() + o.getAge()));
        }
    
        public static void main(String[] args) {
    
            init();
    
            filter();
            // joinId();
            // sort();
            // sum();
            // getIdList();
    
            print();
        }
    }

源代码：[https://github.com/wu-boy/parker][https_github.com_wu-boy_parker] parker-common模块。  
参考资料：《Java8函数式编程》，译者王群锋。

[https_github.com_wu-boy_parker]: https://github.com/wu-boy/parker