What is Composition in Java?

// Java program to Illustrate Concept of Composition

// Importing required classes

import java.io.*;

import java.util.*;

// Class 1

// Helper class

// Book class

class Book {

// Member variables of this class

public String title;

public String author;

// Constructor of this class

Book(String title, String author)

{

// This keyword refers top current instance

this.title = title;

this.author = author;

}

}

// Class 2

// Helper class

// Library class contains list of books.

class Library {

// Reference to the list of books.

private final List<Book> books;

// Constructor of this class

Library(List<Book> books)

{

// This keyword refers to current instance 

this.books = books;

}

// Method of this class

// Getting the list of books

public List<Book> getListOfBooksInLibrary()

{

return books;

}

}

// Class 3

// Main class

class Infinity_board {

// Main driver method

public static void main(String[] args)

{

// Creating the objects of first class 

// inside main() method

Book b1

= new Book("EffectiveJ Java", "Infinity");

Book b2

= new Book("Thought in Java", "Board");

Book b3 = new Book("Java: Best website",

"Board Infinity");

// Creating the list of

// no. of books.

List<Book> book = new ArrayList<Book>();

// Adding books to List object

// using standard add() method

book.add(b1);

book.add(b2);

book.add(b3);

// Creating an object of second class

Library library = new Library(book);

// Calling method of class 2 and storing list of

// books in List Here List is declared of type

// Books(user-defined)

List<Book> books

= library.getListOfBooksInLibrary();

// Iterating over for each loop

for (Book bk : books) {

// Print and display the title and author of