Question

Answer the following Java Collection/Map Question:

The Map interface has a method putAll() that adds all entries in map2 into map1. Write your own putAll2 method ( a generic method), given the two maps as parameters the method will add all entries in map2 into map1 and print map1. Show that the method is working in an application class.

Answer 1

Program : Created as PutAll2.java in Eclipse

import java.util.*;
public class PutAll2
{   
void putAll2(Map m2, Map m1)
   {
       Set<Map.Entry<String, Double>> mentry = m2.entrySet();//Creating set
Iterator<Map.Entry<String, Double>> mapIterator = mentry.iterator();//Creating Iterator
while (mapIterator.hasNext())
{
Map.Entry<String, Double> entry = mapIterator.next();
m1.put(entry.getKey(),entry.getValue());//adding map2 element into map1
}
   }
public static void main(String[] args)
{   
PutAll2 mp = new PutAll2();//Creating object of class
Map<String, String> map2 = new HashMap<>(); //creating map2
map2.put("1", "A"); //Adding element to map2
map2.put("2", "B");
map2.put("3", "C");
map2.put("4", "D");
map2.put("5", "E");
System.out.println("Elements in Map2:");
System.out.println(map2); //Printing content of map 2
Map<String, String> map1 = new HashMap<>();//Creating map1
mp.putAll2(map2,map1);//Passing map2 and map1 to method
System.out.println("Elements in Map1:");
System.out.println(map1); //Printing content of map 1   
}
}

Explanation : map2 is created using HashMap. Elements are added into map2. map1 is also created and pass both map1 and map2 to the method putAll2. Which put all elements in map2 into map1. Content of both map is displayed.

Screenshot :