Java Challenge - Prime Number Finder

This community-built FAQ covers the “Prime Number Finder” code challenge in Java. You can find that challenge here, or pick any challenge you like from our list.

Top Discussions on the Java challenge Prime Number Finder

There are currently no frequently asked questions or top answers associated with this challenge – that’s where you come in! You can contribute to this section by offering your own questions, answers, or clarifications on this challenge. Ask a question or post a solution by clicking reply (reply) below.

If you’ve had an “aha” moment about the concepts, formatting, syntax, or anything else with this challenge, consider sharing those insights! Teaching others and answering their questions is one of the best ways to learn and stay sharp.

Join the Discussion. Help a fellow learner on their journey.

Ask or answer a question about this exercise by clicking reply (reply) below!
You can also find further discussion and get answers to your questions over in #get-help.

Agree with a comment or answer? Like (like) to up-vote the contribution!

Need broader help or resources? Head to #get-help and #community:tips-and-resources. If you are wanting feedback or inspiration for a project, check out #project.

Looking for motivation to keep learning? Join our wider discussions in #community

Learn more about how to use this guide.

Found a bug? Report it online, or post in #community:Codecademy-Bug-Reporting

Have a question about your account or billing? Reach out to our customer support team!

None of the above? Find out where to ask other questions here!

import java.util.*;

public class PrimeFinder {
  public static void main(String[] args) {
    System.out.println(primeFinder(13));
  }

  public static ArrayList primeFinder(int n) {
    ArrayList<Integer> primeNumbers = new ArrayList<Integer>();
    if(n<2) {
      return primeNumbers;
    }
    for (int i=2; i<=n; i++){
      for(int j=2; j<=i; j++){
        if(i%j==0 && i!=j){
          break;
        }else if(i==j){
          primeNumbers.add(j);
        }
      }
    }

    return primeNumbers;
  }
}
import java.util.*;

public class PrimeFinder {
  public static void main(String[] args) {
    System.out.println(primeFinder(13));
  }

  public static ArrayList primeFinder(int n) {
    // Write your code here
    ArrayList<Integer> arr = new ArrayList<>();

    if(n == 1)
    {
      return arr;
    }

    for(int i = 1; i <= n; i++)
    {
      int counter = 0;
      for(int j = 2; j <= i/2; j++)
      {
        if(i % j == 0)
        {
          counter++;
        }
      }

      if(counter == 0 && i != 1)
      {
        arr.add(i);
      }
    }

    return arr;
  }
}
import java.util.*;

public class PrimeFinder {
  public static void main(String[] args) {
    System.out.println(primeFinder(13));
  }

  public static ArrayList primeFinder(int n) {
 ArrayList<Integer> integerArray = new ArrayList<Integer>();
        
        for (int i = 1; i <= n; i++) {
            int count = 0;
            for (int j = i; j >= 1; j--) {
                if (i % j == 0) {
                    count++;
                }
            }
            if (count == 2) {
                integerArray.add(i);
            }
              
        }
        return integerArray;
  }
}
import java.util.ArrayList;

public class PrimeFinder {
    public static void main(String[] args) {
        System.out.println(primeFinder(13));
    }

    public static ArrayList primeFinder(int n) {
       ArrayList <Integer> out = new ArrayList<>();
       for (int i = 2; i <= n; i++){
           boolean isPrime = true;
           for (int j = 2; j < i; j++){
               if (i % j == 0) {
                   isPrime = false;
                   break;
               }
           }
           if (isPrime) out.add(i);
       }
       return out;
    }
}
import java.util.*;

public class PrimeFinder {
  public static void main(String[] args) {
    System.out.println(primeFinder(13));
  }

  public static ArrayList primeFinder(int n) {
    // Write your code here
    ArrayList result = new ArrayList();
    for(int i=2;i<=n;i++){
      if(isPrime(i)){
        result.add(i);
      }
    }
    return result;
  }

  public static boolean isPrime(int n) {
    int count = 0;
    boolean result;
    for(int i=1;i<=n;i++){
      if(n%i==0){
        count++;
      }
    }
    System.out.printf("%d%d\n", count, n);
    result = count == 2?true:false;
    return result;
  }
}