immutable-deepcopy

gistfile1.txt

// Java Program to Create An Immutable Class

import java.util.HashMap;
import java.util.Map;

final class Student {

	private final String name;
	private final int rollNo;
	private final Map<String, String> map1;

	public Student(String name, int rollNo, Map<String, String> map1)
	{

		this.name = name;
		this.rollNo = rollNo;
		Map<String, String> tempMap = new HashMap<>();
		for (Map.Entry<String, String> entry :
			metadata.entrySet()) {
			tempMap.put(entry.getKey(), entry.getValue());
		}
		this.map1 = tempMap;
	}


	public String getName() { return name; }


	public int getRollNo() { return rollNo; }

	// Note that there should not be any setters

	public Map<String, String> getMap1()
	{

		// Creating Map with HashMap reference
		Map<String, String> tempMap = new HashMap<>();

		for (Map.Entry<String, String> entry :
			this.map1.entrySet()) {
			tempMap.put(entry.getKey(), entry.getValue());
		}
		return tempMap;
	}
}



class Main1 {


	public static void main(String[] args)
	{

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

		Student s = new Student("John", 101, map);
		
		System.out.println(s.getName());
		System.out.println(s.getRollNo());
		System.out.println(s.getMap1());

		map.put("3", "third"); // Remains unchanged due to deep copy in constructor
		
		System.out.println(s.getMap1());
		
		s.getMap1().put("4", "fourth"); // Remains unchanged due to deep copy in getter
		
		System.out.println(s.getMap1());
	}
}