Java Instanceof keyword-HackerRank Solution

The Java instanceof operator is used to test if the object or instance is an instanceof the specified type.

In this problem we have given you three classes in the editor:

• Student class
• Rockstar class
• Hacker class

In the main method, we populated an ArrayList with several instances of these classes. count method calculates how many instances of each type is present in the ArrayList. The code prints three integers, the number of instance of Student class, the number of instance of Rockstar class, the number of instance of Hacker class.

 

But some lines of the code are missing, and you have to fix it by modifying only 3 lines! Don't add, delete or modify any extra line.To restore the original code in the editor, click on the top left icon in the editor and create a new buffer.

Sample Input 

 5
 Student
 Student
 Rockstar
 Student
 Hacker

Sample Output

 

 3 1 1

Solution

 

 import java.util.*;


 class Student{}
 class Rockstar{   }
 class Hacker{}


 public class InstanceOFTutorial{
   
   static String count(ArrayList mylist){
      int a = 0,b = 0,c = 0;
      for(int i = 0; i < mylist.size(); i++){
         Object element=mylist.get(i);
         if(element instanceof Student)
            a++;
         if(element instanceof Rockstar)
            b++;
         if(element instanceof Hacker)
            c++;
      }
      String ret = Integer.toString(a)+" "+ Integer.toString(b)+" "+   Integer.toString(c);
      return ret;
   }

   public static void main(String []args){
      ArrayList mylist = new ArrayList();
      Scanner sc = new Scanner(System.in);
      int t = sc.nextInt();
      for(int i=0; i<t; i++){
         String s=sc.next();
         if(s.equals("Student"))mylist.add(new Student());
         if(s.equals("Rockstar"))mylist.add(new Rockstar());
         if(s.equals("Hacker"))mylist.add(new Hacker());
      }
      System.out.println(count(mylist));
   }
 }

 

The instanceof operator of Java is used to determine whether an object(pointed by a reference variable) matches with a specified type or not. This type could be a concrete class-type, an abstract class-type or an interface-type.