Question

Apply The knowledge of “Mapping Models to code” Concept to write Chunks of java
code which maps the following relationships:
a. Aggregation
b. Composition
c. Generalization
d. Realization
e. Dependency

Answer 1

Aggregation Example HAS A Relationship

class Author
{
String authorName;
int age;
String place;

// Author class constructor
Author(String name, int age, String place)
{
this.authorName = name;
this.age = age;
this.place = place;
}
}

class Book
{
String name;
int price;
// author details
Author auther;
Book(String n, int p, Author auther)
{
this.name = n;
this.price = p;
this.auther = auther;
}
public static void main(String[] args) {
Author auther = new Author("John", 42, "USA");
Book b = new Book("Java for Begginer", 800, auther);
System.out.println("Book Name: "+b.name);
System.out.println("Book Price: "+b.price);
System.out.println("------------Auther Details----------");
System.out.println("Auther Name: "+b.auther.authorName);
System.out.println("Auther Age: "+b.auther.age);
System.out.println("Auther place: "+b.auther.place);
}
  
}

Composition Example Part Of Relationship

// Java program to illustrate
// the concept of Composition
import java.io.*;
import java.util.*;

// class book
class Book
{

   public String title;
   public String author;
  
   Book(String title, String author)
   {
      
       this.title = title;
       this.author = author;
   }
}

// Libary class contains
// list of books.
class Library
{

   // reference to refer to list of books.
   private final List<Book> books;
  
   Library (List<Book> books)
   {
       this.books = books;
   }
  
   public List<Book> getTotalBooksInLibrary(){
      
   return books;
   }
  
}

// main method
class GFG
{
   public static void main (String[] args)
   {
      
       // Creating the Objects of Book class.
       Book b1 = new Book("EffectiveJ Java", "Joshua Bloch");
       Book b2 = new Book("Thinking in Java", "Bruce Eckel");
       Book b3 = new Book("Java: The Complete Reference", "Herbert Schildt");
      
       // Creating the list which contains the
       // no. of books.
       List<Book> books = new ArrayList<Book>();
       books.add(b1);
       books.add(b2);
       books.add(b3);
      
       Library library = new Library(books);
      
       List<Book> bks = library.getTotalBooksInLibrary();
       for(Book bk : bks){
          
           System.out.println("Title : " + bk.title + " and "
           +" Author : " + bk.author);
       }
   }
}

Generalization Example

class Father {
   public void work()
   {
       System.out.println("Earning Father");
   }
}

class Son extends Father {
   public void play()
   {
       System.out.println("Enjoying son");
   }
}

class Main {
   public static void main(String[] args)
   {
       // father is a superclass reference
       Father father;

       // new operator returns a subclass reference
       father = (Father) new Son();

       // which is widened using casting
       // and stored in father variable
       // Though casting is done but it is not needed
       father.work();

       // Uncomment next lone to see the error
       // father.play();
   }
}

Realization Example Implementing the interface

public interface Figure {
    public double area();
}

public class Rectangle implements Figure {

    public double length = 10.0;
    public double width = 10.0;

    public double area() {

        return length * width;
    }
}

public class Circle implements Figure {
    public double pie = 3.27;
    public double radius = 5.0;

    public double area() {

        return pie * radius * radius;
    }
}

Dependency Example dependent upon something (use of this keyword)

import java.util.logging.Logger;

public class MyClass

{

private Logger logger;

public MyClass(Logger logger)

{

this.logger = logger;

logger.info("This is a log message.")

}

}

You can also do integration of all part of things to make a whole java project. and these examples given here are independent of each other.

Thanks.