Collectors.groupingBy 使用

 

本文主要介绍一下lambda表达式中的Collectors.groupingBy的使用。

//groupingBy使用
        System.out.println("=======groupingBy==========");
        Stream stream = Stream.of(new Person("1", "aa", "12"), new Person("1", "bb", "13"), new Person("3", "cc", "14"));
        System.out.println(stream.collect(Collectors.groupingBy(x -> x.id)));
 
        //groupingBy
        Map> tempMap = Stream.of(new Person("1", "aa", "12"), new Person("1", "bb", "13"), new Person("3", "cc", "14"))
                .collect(Collectors.groupingBy(x -> x.id));
        for (String s : tempMap.keySet()) {
            tempMap.get(s).stream().forEach(x -> System.out.println(x));
        }
 
        Map> collectGroup = Stream.of(1, 2, 3, 4)
                .collect(Collectors.groupingBy(it -> it > 3));
        System.out.println("collectGroup : " + collectGroup);

这里用到的Person类的代码：

class Person {
    String id;
    String name;
    String age;
 
    public String getId() {
        return id;
    }
 
    public void setId(String id) {
        this.id = id;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public String getAge() {
        return age;
    }
 
    public void setAge(String age) {
        this.age = age;
    }
 
    public Person() {
    }
 
    public Person(String id, String name, String age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }
 
    @Override
    public String toString() {
        return "Person{" +
                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                ", age='" + age + '\'' +
                '}';
    }
}

看一下运行结果：