JAVA EE: How to find the oldest male person using max method of Java 8 Stream

Monday 16 October 2017

How to find the oldest male person using max method of Java 8 Stream | Streams in Java 8

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Person.java

enum Gender
{
    MALE, FEMALE
}

public class Person
{
    private String name;
    private String email;
    private Gender gender;
    private int age;

    public Person(String name, String email, Gender gender, int age)
    {
        super();
        this.name = name;
        this.email = email;
        this.gender = gender;
        this.age = age;
    }

    public String getName()
    {
        return name;
    }

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

    public String getEmail()
    {
        return email;
    }

    public void setEmail(String email)
    {
        this.email = email;
    }

    public Gender getGender()
    {
        return gender;
    }

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

    public int getAge()
    {
        return age;
    }

    public void setAge(int age)
    {
        this.age = age;
    }

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

}

StreamMaxDemo.java

import java.util.ArrayList;
import java.util.List;
import java.util.Optional;

public class StreamMaxDemo
{
    public static void main(String[] args)
    {
        List<Person> personList = new ArrayList<>();

        personList.add(new Person("Alice","alice@gmail.com",    Gender.FEMALE, 26));
        personList.add(new Person("Bob","bob@gmail.com", Gender.MALE, 32));
        personList.add(new Person("Carol","carol@gmail.com",Gender.FEMALE, 23));
        personList.add(new Person("David","david@gmail.com",    Gender.MALE, 39));
        personList.add(new Person("Eric","eric@gmail.com", Gender.MALE, 26));
        
        /*
         * Similar to the min() operation, the max() is a special reduction
         * operation that returns the maximum element in the stream according to
         * the specified comparator.
         * 
         * The following code finds the oldest male person in the list:
         */
        Optional<Person> optional = personList.stream()
                .filter(p -> p.getGender().equals(Gender.MALE))
                .max((p1, p2) -> p1.getAge() - p2.getAge());
        if (optional.isPresent())
        {
            Person oldestMan = optional.get();
            System.out.println("The oldest man is: " + oldestMan.getName()
                    + " (" + oldestMan.getAge() + ")");
        }

    }

}