Introduction

This program helps to reverse Key to Value and Value to Key for a Map Data Structure. There are various ways to write the program and the KW team will prepare a program using a few of them. Please find the program written in Java Programming Language below –

Program Code

package com.kw.sample;

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

import org.apache.commons.collections.MapUtils;

/**
 * This class helps to explain reverse a Map.
 * 
 */
public class KWReverseMap {

	/**
	 * This method helps to start the program execution.
	 * 
	 * @param args
	 */
	public static void main(String[] args) {

		System.out
				.println("*********** Reverse Map Program Started *************");
		// Instantiate Map object
		Map<String, String> map = new HashMap<String, String>();
		// Add the Key and Value
		map.put("a", "1");
		map.put("d", "1");
		map.put("b", "2");
		map.put("c", "3");
		map.put("d", "4");
		map.put("d", "41");

		// Call the method to reverse the Map Key Value
		reverseAMap1(map);


		System.out.println(invertMap(map));
	}

	/**
	 * This method helps to reverse the Key to Value and Value to Key for a Map.
	 * 
	 * @param map
	 */
	private static void reverseAMap1(Map map) {

		System.out.println("+++++ Original Map Elements ++++++");
		// Print the Map elements
		System.out.println(map);
		// Call method to revert the Map using invertMap from MapUtils class.
		// This class available in Apace Common Jar file and it should be there
		// in the class path.
		Map<String, String> test1 = MapUtils.invertMap(map);

		System.out.println("+++++ Map Elements After Reverse ++++++");
		// Print the Map elements
		System.out.println(test1);
	}

	/**
	 * This method helps to invert the Maps Key Value Pair interchangeable.
	 * 
	 * @param <A>
	 * @param <B>
	 * @param map
	 * @return
	 */
	private static <A, B> Map<B, A> invertMap(Map<A, B> map) {
		System.out.println("*********** invertMap Method *************");
		Map<B, A> reverseMap = new HashMap();
		for (Map.Entry<A, B> entry : map.entrySet()) {
			reverseMap.put(entry.getValue(), entry.getKey());
		}
		return reverseMap;
	}
}

Output

*** Reverse Map Program Started *** +++++ Original Map Elements ++++++ {d=41, b=2, c=3, a=1} +++++ Map Elements After Reverse ++++++ {3=c, 2=b, 1=a, 41=d} * invertMap Method *
{3=c, 2=b, 1=a, 41=d}