FinalClassExample.java

package com.demo.program.immutable;

import java.util.HashMap;
import java.util.Iterator;



public final class FinalClassExample {

    private final int id;

    private final String name;

    private final HashMap<String, String> testMap;

    public int getId() {
        return id;
    }


    public String getName() {
        return name;
    }

    /**
     * Accessor function for mutable objects
     */
    @SuppressWarnings("unchecked")
	public HashMap<String, String> getTestMap() {
        //return testMap;
        return (HashMap<String, String>) testMap.clone();
    }

    /**
     * Constructor performing Deep
     *
     * @param i
     * @param n
     * @param hm
     */

    public FinalClassExample(int i, String n, HashMap<String, String> hm) {
        System.out.println("Performing Deep for Object initialization");
        this.id = i;
        this.name = n;

        HashMap<String, String> tempMap = new HashMap<>();
        String key;

        Iterator<String> it = hm.keySet().iterator();

        while (it.hasNext()) {
            key = it.next();
            tempMap.put(key, hm.get(key));
        }
        this.testMap = tempMap;
    }


    /**
     * Constructor performing Shallow
     * @param i
     * @param n
     * @param hm
     */
    /**
     public FinalClassExample(int i, String n, HashMap<String,String> hm){
     System.out.println("Performing Shallow  for Object initialization");
     this.id=i;
     this.name=n;
     this.testMap=hm;
     }
     */

    /**
     * To test the consequences of Shallow  and how to avoid it with Deep  for creating immutable classes
     *
     * @param args
     */
    public static void main(String[] args) {


        HashMap<String, String> h1 = new HashMap<String, String>();
        h1.put("1", "first");
        h1.put("2", "second");

        String s = "original";

        int i = 10;

        FinalClassExample ce = new FinalClassExample(i, s, h1);

        //Lets see whether its copy by field or reference
        System.out.println(s == ce.getName());
        System.out.println(h1 == ce.getTestMap());
        //print the ce values
        System.out.println("ce id:" + ce.getId());
        System.out.println("ce name:" + ce.getName());
        System.out.println("ce testMap:" + ce.getTestMap());
        //change the local variable values
        i = 20;
        s = "modified";
        h1.put("3", "third");
        //print the values again
        System.out.println("ce id after local variable change:" + ce.getId());
        System.out.println("ce name after local variable change:" + ce.getName());
        System.out.println("ce testMap after local variable change:" + ce.getTestMap());

        HashMap<String, String> hmTest = ce.getTestMap();
        hmTest.put("4", "new");

        System.out.println("ce testMap after changing variable from accessor methods:" + ce.getTestMap());

    }

}