What's the purpose of partitioningBy

Question

For example, if I intend to partition some elements, I could do something like:

Stream.of(\"I\", \"Love\", \"Stack Overflow\")
      .collect(Collectors.part         


        

Answer 1

partitioningBy method will return a map whose key is always a Boolean value, but in case of groupingBy method, the key can be of any Object type

//groupingBy
Map> list2 = new HashMap>();
list2 = list.stream().collect(Collectors.groupingBy(p->p.getAge()==22));
System.out.println("grouping by age -> " + list2);

//partitioningBy
Map> list3 = new HashMap>();
list3 = list.stream().collect(Collectors.partitioningBy(p->p.getAge()==22));
System.out.println("partitioning by age -> " + list2);

As you can see, the key for map in case of partitioningBy method is always a Boolean value, but in case of groupingBy method, the key is Object type

Detailed code is as follows:

    class Person {
    String name;
    int age;

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

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public String toString() {
        return this.name;
    }
}

public class CollectorAndCollectPrac {
    public static void main(String[] args) {
        Person p1 = new Person("Kosa", 21);
        Person p2 = new Person("Saosa", 21);
        Person p3 = new Person("Tiuosa", 22);
        Person p4 = new Person("Komani", 22);
        Person p5 = new Person("Kannin", 25);
        Person p6 = new Person("Kannin", 25);
        Person p7 = new Person("Tiuosa", 22);
        ArrayList list = new ArrayList<>();
        list.add(p1);
        list.add(p2);
        list.add(p3);
        list.add(p4);
        list.add(p5);
        list.add(p6);
        list.add(p7);

        // groupingBy
        Map> list2 = new HashMap>();
        list2 = list.stream().collect(Collectors.groupingBy(p -> p.getAge() == 22));
        System.out.println("grouping by age -> " + list2);

        // partitioningBy
        Map> list3 = new HashMap>();
        list3 = list.stream().collect(Collectors.partitioningBy(p -> p.getAge() == 22));
        System.out.println("partitioning by age -> " + list2);

    }
}