对Java8 stream的简单实践

Posted 2021-01-25 苍青浪

最近学习很多Java8方面的新特性，特地做了一些简单的实践和总结。

import java.util.*;
import java.util.stream.Collectors;

public class StreamTest {
    static class User{
        private String name;
        private int age;

        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 User(String name, int age) {
            this.name = name;
            this.age = age;
        }

        @Override
        public String toString() {
            return name;
        }

// 重写hashCode
        @Override
        public int hashCode() {
            int n = 31;
            n = n * 31 + age;
            n = n* 31 + name.hashCode();
            return n;

        }

        @Override
        public boolean equals(Object obj) {
            if (!(obj instanceof User)) {
                return false;
            }
            User user1 = (User) obj;
            return this.name.equals(user1.name)
                    && Integer.valueOf(age).equals(user1.age);
        }
    }
    public static void main(String[] args) {
        List<User> list = new ArrayList<>();
        User user1 = new User("zdx", 12);
        User user2 = new User("zdx1", 12);
        User user3 = new User("zdx2", 18);
        User user4 = new User("zdx3", 22);
        list.add(user1);
        list.add(user2);
        list.add(user3);
        list.add(user4);

        // 将 Stream 转化为List 并且实现去重
        List list1 = list.stream().distinct().collect(Collectors.toList());
        list1.forEach(System.out::println);

        // 将 Stream 转化为 Map
        // 实现此方法需要注意添加进Map的的 key 值不可以重复，否则会抛出异常！！！！
        Map<String, Integer> map = list.stream().collect(Collectors.toMap(User::getName, User::getAge));
        for (String key: map.keySet()) {
            System.out.println(key);
        }


//         去重实现方法一
        List<User> result = new LinkedList<>();
        for (User user : list) {
            boolean b = result.stream().anyMatch(u -> u.name.equals(user.name));
            if (!b) {
                result.add(user);
            }
        }

        result.forEach(System.out::println);


//         利用HashSet实现list的去重
        Set<User> set = new HashSet<>(list);
        set.forEach(System.out::println);
    }
}