This code is the most right code but yet it doesn't works saying * Wrong Answer :( 1/1 test case failed * Sample Test case 0 * Compiler Message * Wrong Answer * Input (stdin) 5 Student Student Rockstar Student Hacker * Your Output (stdout) 3 1 1 * Expected Output 3 1 1

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 []argh)
   {
      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));
   }
}

There is an issue with the testcases for this program

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;

}

This is the code I have written, which passes the testcase, but if I add {} after the if condition as shown below, or try to add any comment, the testcase will fail, which should not happen

if(element instanceof Student) { a++; } //Or if you add any comment like this anywhere in the code, it will fail

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

Use this code This works perfectly 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

This problem helps you understand runtime type checking in Java.

No need to use .getClass() or generics — just use instanceof.

Here is Java InstanceOf Keyword solution - https://programmingoneonone.com/hackerrank-java-instanceof-keyword-problem-solution.html