HashMapArrayListApproach/HashMapFunctionalityWithLoop.java at master · vaibhavchugh09/HashMapArrayListApproach · GitHub

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package com.practice;

import java.util.ArrayList;
import java.util.HashMap;

public class HashMapFunctionalityWithLoop {

	private HashMap<String, ArrayList<String>> hasmp_list;

	private ArrayList<String> aa;

// Try this method and you will get the blank array
	private void wrongApproachExecuteMethod() {

		hasmp_list = new HashMap<String, ArrayList<String>>();
		for (int j = 0; j < 5; j++) {
			for (int i = 0; i < 10; i++) {
				aa = new ArrayList<String>();
				aa.add(String.valueOf(i));

				hasmp_list.put(String.valueOf(j), aa);
				aa.clear(); // here we are clearing the data of arraylist and it will
				// directly reflect with hashmap because of same object.


				System.out.println(String.valueOf(hasmp_list) + " Wrong Execution Method of hashmapValue");

			}
		}

	}

	private void rightApproachExecuteMethod() {

		hasmp_list = new HashMap<String, ArrayList<String>>();
		for (int j = 0; j < 5; j++) {
			for (int i = 0; i < 10; i++) {
				aa = new ArrayList<String>();

				if (hasmp_list.get(String.valueOf(j)) == null) {

					hasmp_list.put(String.valueOf(j), new ArrayList<String>());

				}
				hasmp_list.get(String.valueOf(j)).add(String.valueOf(i));

				aa.clear();

						System.out.println(String.valueOf(hasmp_list) + " Right Execution Method of hashmapValue");


			}
		}

	}

	private void withoutUsingClearMethodWrongApproachExecuteMethod() {

		hasmp_list = new HashMap<String, ArrayList<String>>();
		for (int j = 0; j < 5; j++) {
			for (int i = 0; i < 10; i++) {
				aa = new ArrayList<String>();
				aa.add(String.valueOf(i));

				hasmp_list.put(String.valueOf(j), aa);
				// aa.clear(); // if we comment clear method in this approach

						// this will return you a value which is added last in the arraylist.
						System.out.println(String.valueOf(hasmp_list) + " Wrong Execution Method of hashmapValue");


			}
		}

	}

	public static void main(String[] args) {

		HashMapFunctionalityWithLoop hh = new HashMapFunctionalityWithLoop();
		hh.wrongApproachExecuteMethod();
		hh.rightApproachExecuteMethod();
		hh.withoutUsingClearMethodWrongApproachExecuteMethod();

	}

}