Group List items Several Lists using Stream Java 8

Group List items into Several Lists using Stream in Java 8 is easy.

We have a list of Persons and we want to group them into Female, Male, Unknown list using Stream and Collectors in Java 8.

PersonBean

Below is a simple class that represents a person. It has a name and gender fields. The toString() method has been overridden to display its fields’ contents in human-readable form.

package streamexample.malefemale;

/**
 * Simple JavaBean that represents a person.
 * 
 * @author turreta.com
 *
 */
public class PersonBean {

    private String name;

    // female, male, or unknown
    private String gender;

    public PersonBean(String name, String gender) {
        super();
        this.name = name;
        this.gender = gender;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    @Override
    public String toString() {
        return "PersonBean [name=" + name + ", gender=" + gender + "]";
    }

}

package streamexample.malefemale;

/**

* Simple JavaBean that represents a person.

* @author turreta.com

public class PersonBean {

private String name;

// female, male, or unknown

private String gender;

public PersonBean(String name, String gender) {

super();

this.name = name;

this.gender = gender;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public String getGender() {

return gender;

}

public void setGender(String gender) {

this.gender = gender;

}

@Override

public String toString() {

return "PersonBean [name=" + name + ", gender=" + gender + "]";

}

Main Class

Below is the main class that uses Stream, and Collectors.

package streamexample.malefemale;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class MaleAndFemaleDemo {

    public static void main(String[] args) {

        final String FEMALE = "female";
        final String MALE = "male";
        final String UNKNOWN = "unknown";

        List<PersonBean> listOfPersons = new ArrayList<>();
        listOfPersons.add(new PersonBean("Aiza", FEMALE));
        listOfPersons.add(new PersonBean("Rowena", FEMALE));
        listOfPersons.add(new PersonBean("Mirsa", FEMALE));

        listOfPersons.add(new PersonBean("Allan", MALE));
        listOfPersons.add(new PersonBean("Pedro", MALE));
        listOfPersons.add(new PersonBean("Rody", MALE));

        listOfPersons.add(new PersonBean("Bot1", UNKNOWN));
        listOfPersons.add(new PersonBean("QA", UNKNOWN));
        listOfPersons.add(new PersonBean("TestUser", UNKNOWN));

        Map<String, List<PersonBean>> myMap = splitByGender(listOfPersons.stream());

        myMap.forEach((k, v) -> System.out.println("Gender : " + k + ", Listing : " + v));

    }

    public static Map<String, List<PersonBean>> splitByGender(Stream<PersonBean> stream) {
        return stream.collect(Collectors.groupingBy(person -> person.getGender()));
    }
}

package streamexample.malefemale;

import java.util.ArrayList;

import java.util.List;

import java.util.Map;

import java.util.stream.Collectors;

import java.util.stream.Stream;

public class MaleAndFemaleDemo {

public static void main(String[] args) {

final String FEMALE = "female";

final String MALE = "male";

final String UNKNOWN = "unknown";

List<PersonBean> listOfPersons = new ArrayList<>();

listOfPersons.add(new PersonBean("Aiza", FEMALE));

listOfPersons.add(new PersonBean("Rowena", FEMALE));

listOfPersons.add(new PersonBean("Mirsa", FEMALE));

listOfPersons.add(new PersonBean("Allan", MALE));

listOfPersons.add(new PersonBean("Pedro", MALE));

listOfPersons.add(new PersonBean("Rody", MALE));

listOfPersons.add(new PersonBean("Bot1", UNKNOWN));

listOfPersons.add(new PersonBean("QA", UNKNOWN));

listOfPersons.add(new PersonBean("TestUser", UNKNOWN));

Map<String, List<PersonBean>> myMap = splitByGender(listOfPersons.stream());

myMap.forEach((k, v) -> System.out.println("Gender : " + k + ", Listing : " + v));

}

public static Map<String, List<PersonBean>> splitByGender(Stream<PersonBean> stream) {

return stream.collect(Collectors.groupingBy(person -> person.getGender()));

}

Output

myMap will have 3 lists for each gender – male, female, and unknown.

Gender : female, Listing : [PersonBean [name=Aiza, gender=female], PersonBean [name=Rowena, gender=female], PersonBean [name=Mirsa, gender=female]]
Gender : male, Listing : [PersonBean [name=Allan, gender=male], PersonBean [name=Pedro, gender=male], PersonBean [name=Rody, gender=male]]
Gender : unknown, Listing : [PersonBean [name=Bot1, gender=unknown], PersonBean [name=QA, gender=unknown], PersonBean [name=TestUser, gender=unknown]]

Gender : female, Listing : [PersonBean [name=Aiza, gender=female], PersonBean [name=Rowena, gender=female], PersonBean [name=Mirsa, gender=female]]

Gender : male, Listing : [PersonBean [name=Allan, gender=male], PersonBean [name=Pedro, gender=male], PersonBean [name=Rody, gender=male]]

Gender : unknown, Listing : [PersonBean [name=Bot1, gender=unknown], PersonBean [name=QA, gender=unknown], PersonBean [name=TestUser, gender=unknown]]