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Stream 流之 distinct

一、方法概述

如果想要对流中元素进行去重可以使用 distinct 方法

二、案例

1、根据 hashcode 和 equal 进行去重

public class StreamDemo {
    public static void main(String[] args) {
        List<Person> personList = Arrays.asList(
                new Person(1, "大毛", 30, 175),
                new Person(2, "二毛", 25, 170),
                new Person(2, "二毛", 25, 170),
                new Person(4, "小毛", 30, 175));
 
        // 获取 person 类型流
        Stream<Person> personStream = personList.stream();
        // distinct 方法根据 hashcode 和 equal 方法去判定是否是同一个元素,使用前一定要重写 hashcode 和 equal 方法
        Stream<Person> distinctStream = personStream.distinct();
 
        // 遍历新流 sortedStream 中的元素
        distinctStream.forEach(System.out::println);
    }
}

2、自定义去重(根据指定属性进行去重)

public class StreamDemo {
    public static void main(String[] args) {
        List<Person> personList = Arrays.asList(
                new Person(1, "大毛", 30, 175),
                new Person(2, "二毛", 25, 170),
                new Person(2, "三毛", 25, 170),
                new Person(4, "小毛", 30, 175));
 
        // 获取 person 类型流
        Stream<Person> personStream = personList.stream();
        // 根据自定义的 key 去重
        Stream<Person> distinctStream = personStream.filter(distinctByKey((item) -> item.getAge() + "@" + item.getHeight()));
        // 遍历新流 sortedStream 中的元素
        distinctStream.forEach(System.out::println);
    }
 
    // 自定义去重方法
    static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {
        Map<Object, Boolean> seen = new ConcurrentHashMap<>();
        return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
    }
}