Question

HashMap is a Map based collection class that is used for storing Key & value pairs, it is denoted as HashMap<Key, Value> or HashMap<K, V>. This class makes no guarantees as to the order of the map. It is similar to the Hashtable class except that it is unsynchronized and permits nulls(null values and null key).

5.Write a Java program to test if a map contains a mapping for the specified key.a.Add values in the Hash mapb.Printthe mapc.Check for a specified key, print result

6.Write a Java program to copy all of the mappings from the specified map to another map. Use iterator with both for each and whileloop,print out the key with the matching value.

You can combine them into one single program.

Answer 1

5 ).

Code:

package demo;

import java.util.HashMap;
import java.util.Scanner;

public class HashMap1 {

   public static void main(String[] args) {
//       create a hashmap
       HashMap<Integer,String> map=new HashMap<Integer,String>();

       //       create a scanner object
       Scanner in = new Scanner(System.in);
      
//       put values into the map like student roll number and name
       map.put(1,"Arjun"); //Put elements in Map
       map.put(2,"Ravi");
       map.put(3,"Kiran");   
       map.put(4,"Suresh");
       map.put(5, "Tarun");
         
//       print the map
       System.out.println(map);
         
//       read the search key from the user
       System.out.println("Enter the key to Search");
         
       int key = in.nextInt();
         
//       check if the entered key is present or not
       if(map.containsKey(key)){
   System.out.println("The hashmap contains key " + key+" value is " + map.get(key));
   }
      
//       if the key is not present
       else {
   System.out.println("The hashmap does not contains key "+key);
   }
   }

}

//--------------------------------------------------------------------------------------------------------------------------------------------------------

6 ).

Code:

package demo;

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

public class HashMap2 {

   public static void main(String[] args) {
      
//       create two hashmaps map1 and map2
       HashMap<Integer,String> map1=new HashMap<Integer,String>();//Creating HashMap
       HashMap<Integer,String> map2=new HashMap<Integer,String>();
      
//       insert elements into the hash map for example key is roll number and name is value
   map1.put(1,"Arjun");
   map1.put(2,"Ravi");
   map1.put(3,"Kiran");   
   map1.put(4,"Suresh");
   map1.put(5, "Tarun");
     
//   insert some student names and roll numbers to map2
   map2.put(6,"Karna"); //Put elements in Map
   map2.put(7,"Narayana");
   map2.put(8,"Surya");   
   map2.put(9,"Shiva");
   map2.put(10, "Kanish");
     
     
//   copy all the map1 elements to map2
   map2.putAll(map1);
     
   System.out.println("...................ForEach...........................");
     
//   iteration using for each through the map2
   map2.forEach((k,v) -> System.out.println("Key - "+ k + " & " +"Value - "+ v));
     
     
     
     
   System.out.println(".................Using while loop.........................");

//   using while loop to print hash map
//   create an object for iterator and use it to print hashmap
     
   Iterator iterator = map2.entrySet().iterator();
     
//   check if the hash map contains next element
while (iterator.hasNext()) {
     
//       
Map.Entry entry = (Map.Entry) iterator.next();
  
// print the key and value

System.out.println("Key - "+entry.getKey()+" & Value - "+ entry.getValue());
}
   }
}