JAVA EE: How to get the sum of ages of all male authors younger than 50

Tuesday 18 July 2017

How to get the sum of ages of all male authors younger than 50 | Java 8 streams tutorial

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https://www.youtube.com/watch?v=_kVLMbpop-I&list=UUhwKlOVR041tngjerWxVccw

Author.java

public class Author
{
    private String name;
    private String email;
    private int age;
    private char gender;

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

    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 int getAge()
    {
        return age;
    }

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

    public char getGender()
    {
        return gender;
    }

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

}

Book.java

public class Book
{

    private String name;
    private Author author;
    private double price;

    public Book(String name, Author author, double price)
    {
        super();
        this.name = name;
        this.author = author;
        this.price = price;
    }

    public String getName()
    {
        return name;
    }

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

    public Author getAuthor()
    {
        return author;
    }

    public void setAuthor(Author author)
    {
        this.author = author;
    }

    public double getPrice()
    {
        return price;
    }

    public void setPrice(double price)
    {
        this.price = price;
    }

}

StreamDemo.java

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

/**
 *
 * How to get the sum of ages of all male authors younger than 50.
 *
 */
public class StreamDemo
{
    public static void main(String[] args)
    {
        List<Book> bookList = new ArrayList<Book>();

        // Adding Books
        bookList.add(new Book("Java Basics",
                new Author("Peter", "peter@yahoo.com", 20, 'M'),1000.50));

        bookList.add(new Book("Mysql Basics",
                new Author("Steve", "steve@yahoo.com", 30, 'M'),2000.0));

        bookList.add(new Book("Oracle Basics",
                new Author("John", "john@yahoo.com", 40, 'M'),3000.0));

        bookList.add(new Book("Angular Basics",
                new Author("Juli", "juli@yahoo.com", 55, 'F'),3000.0));

        bookList.add(new Book("Jquery Basics",
                new Author("Dave", "dave@yahoo.com", 65, 'M'),1000.0));

        /*
         * Using the same original stream we once again map the
         * elements from Books to Authors and filter just on those
         * authors that are male. Next we map the elements from
         * Authors to author ages which gives us a stream of ints. We
         * filter ages to just those that are less than 50 and use a
         * reduce operation and Integer::sum to total the ages.
         */

        Integer sumOfMaleAuthorAge = 
                 bookList.stream()//Stream<Book>
                .map(Book::getAuthor) //Stream<Book> to Stream<Author>.
                .filter(author -> author.getGender() == 'M') // filter the male Authors.
                .map(Author::getAge)//Stream<Author> to Stream<age>.
                .filter(age -> age < 50)//filter the age<50.
                .reduce(0, Integer::sum);// calculate the sum of ages.

        System.out.println("sumOfMaleAuthorAge = " + sumOfMaleAuthorAge);

    }
}