Prime number generator program missing return statement

**03EVOAWD** · September 8th, 2009, 08:33 AM

Below is what I am trying to get to but I keep getting a compiler error of a missing return statement that looks like this:

PrimeNumber.java:85: missing return statement
}//End Method

I dont understand the error and cant find an explination that I like to make me get it anywhere.

Declare a method to determine whether an integer is a prime number
Use the following method declarations: public static Boolean isPrime (int num)
An integer greater than 1 is a prime number if its only divisor is 1 or itself.
For example, isPrime (11) returns true, and isPrime (9) returns false.

Us the isPrime method to find the first thousand prime numbers and display every ten prime numbers in a row, as follows:

2 3 5 7 11 13 17 19 23 29
31 37 41 43 47 53 59 61 67 71
73 79 83 89 97 … …

Important Notes: The input and output must use JOptionPane dialog and display boxes.

 
import javax.swing.*;
import java.util.Scanner;
 
public class PrimeNumber{
 
    public static boolean isPrime(int num){
 
        Scanner input = new Scanner(System.in);
 
        int Odd = input.nextInt();
        int Count = 0;
        int Prime = 1;
        int Num1;
 
    String checker=
        JOptionPane.showInputDialog("Input your Values:");
        Integer Number1 = Integer.parseInt(checker);
 
    do{
 
        Num1 = (Prime + 2) / 2;
 
 
        boolean isPrime = true;
        Count++;
 
        if(Num1 != 1){
        isPrime = false;
        break;}
}
 
     while(Count <= 1000);    
 
    String message2=
        String.format("All Prime Numbers: %d\n", Odd);    
        JOptionPane.showMessageDialog(null, message2);
 
    }//End method 
 
}//End Class PrimeNumber

**JavaPF** · September 8th, 2009, 08:57 AM

Hello 03EVOAWD.

You are getting this error because of this method:

public static boolean isPrime(int num) {
 
}

You need to return a result of type boolean.

For example:

 
import javax.swing.*;
import java.util.Scanner;
 
public class PrimeNumber{
 
    public static boolean isPrime(int num){
 
        Scanner input = new Scanner(System.in);
 
        int Odd = input.nextInt();
        int Count = 0;
        int Prime = 1;
        int Num1;
 
    String checker=
        JOptionPane.showInputDialog("Input your Values:");
        Integer Number1 = Integer.parseInt(checker);
 
    do{
 
        Num1 = (Prime + 2) / 2;
 
 
        boolean isPrime = true;
        Count++;
 
        if(Num1 != 1){
        isPrime = false;
        break;}
}
 
     while(Count <= 1000);    
 
    String message2=
        String.format("All Prime Numbers: %d\n", Odd);    
        JOptionPane.showMessageDialog(null, message2);
        [B]return false;[/B]
 
    }//End method 
 
}//End Class PrimeNumber

I'm not sure if this will work as expected but it will stop that error.

**03EVOAWD** · September 8th, 2009, 09:12 AM

Thanks it did stop that error and the program compiles now.....

But alas another error:
Exception in thread "main" java.lang.NoSuchMethodError:main

Gotta love it

**JavaPF** · September 8th, 2009, 09:30 AM

Ummmm try adding:

public static void main(String[] args){
 
}

You will need to call your boolean method from within this main method.

**helloworld922** · September 8th, 2009, 09:54 AM

Ooh... don't compute every prime seprately

If you know what range you need prime numbers up to, use the Sieve of Eratosthenes, or if you're feeling bold the Sieve of Atkin.

**03EVOAWD** · September 8th, 2009, 10:01 AM

I have called the method in a seperate class and now there are no errors at all not in compiling or running but when I run the program nothing happens...

updated program caller is located below

import javax.swing.*;
import java.util.Scanner;
 
public class PrimeNumber{
 
public static boolean isPrime(int num){
 
		Scanner input = new Scanner(System.in);
 
		int Odd = input.nextInt();
		int Count = 0;
		int Prime = 1;
		int Num1;
 
	String checker=
		JOptionPane.showInputDialog("Input your values:");	
		int number1 = Integer.parseInt(checker);
 
	do{
 
		Num1 = (Prime + 2) / 2;
 
 
		boolean isPrime = true;
		Count++;
 
		if(Num1 != 1){
		isPrime = false;
		break;}
}
 
 	while(Count <= 1000);
 
	String message2=
		String.format("Total number of Entries: %d\n", Odd);	
		JOptionPane.showMessageDialog(null, message2);
		return false;                   
 
 
}//End method main
 
}//End Class PrimeNumber

Used to call the method

public class Tester{
 
public static void main(String[] args){
 
PrimeNumber method = new PrimeNumber();
 
 
}//End method main
 
}//End Class Tester

**JavaPF** · September 8th, 2009, 10:08 AM

What are you expecting to happen?

**03EVOAWD** · September 8th, 2009, 10:21 AM

find the first thousand prime numbers and display every ten prime numbers in a row, ----eventually

Right now I just want it to ask me to input a value

**JavaPF** · September 8th, 2009, 11:20 AM

Originally Posted by 03EVOAWD

find the first thousand prime numbers and display every ten prime numbers in a row, ----eventually

Right now I just want it to ask me to input a value

System.out.println("Enter a value: ");
Scanner input = new Scanner(System.in);
int Odd = input.nextInt();

**03EVOAWD** · September 9th, 2009, 03:55 PM

Okay I made some progress......

I decided to just get it working in the CMD prompt and then worry about JOptionPane later now I cant get it to print in JOptionPane like it does in the CMD Prompt.

x x x x x x x x x x
x x x x x x x x x x....10 numbers across all the way up to 1000

Any Help is appreciated

import javax.swing.JOptionPane;
 
public class PrimeNumber
{
    public static void main (String[] args)
        {
 
            final int Maximum_Primes = 1000;//Number of primes to display
 
            final int Primes_Per_Line = 10; //Display 10 per line
 
            int count = 0;//Count number of prime numbers
 
            int number = 2;
 
            System.out.println("The first 1000 prime numbers are \n");
 
            while (count < Maximum_Primes)
            {
                boolean isPrime = true;
 
                int temp = number/2; // had to declare new variable since you cannot do math in a for loop
 
                for (int divisor = 2;divisor<=temp;divisor++) //you cannot declare divisor 3 times here and it             
 
                                                              //cannot be split on multiple lines 
                {                  
		    if (number % divisor == 0){
                                isPrime = false;
                                break;
                        }
                }
                if (isPrime)
                {
                    count++;
                    if (count % Primes_Per_Line != 0)//need to make sure that it will print when its not 
                                                                                            // equal to 0
                    {
 
			    System.out.print(number + " ");
                    }
                    else
                            System.out.println(number + ".");
                }
                number++;
            }
        }
}

**JavaPF** · September 10th, 2009, 04:13 AM

Try this. Only problem is it shows each prime number one by one..

import javax.swing.JOptionPane;
 
public class PrimeNumber
{
    public static void main (String[] args)
        {
 
            final int Maximum_Primes = 1000;//Number of primes to display
 
            final int Primes_Per_Line = 10; //Display 10 per line
 
            int count = 0;//Count number of prime numbers
 
            int number = 2;
 
            System.out.println("The first 1000 prime numbers are \n");
 
            while (count < Maximum_Primes)
            {
                boolean isPrime = true;
 
                int temp = number/2; // had to declare new variable since you cannot do math in a for loop
 
                for (int divisor = 2;divisor<=temp;divisor++) //you cannot declare divisor 3 times here and it             
 
                                                              //cannot be split on multiple lines 
                {                  
            if (number % divisor == 0){
                                isPrime = false;
                                break;
                        }
                }
                if (isPrime)
                {
                    count++;
                    if (count % Primes_Per_Line != 0)//need to make sure that it will print when its not 
                                                                                            // equal to 0
                    {
 
                System.out.print(number + " ");
                [B]JOptionPane.showMessageDialog(null, number + " ");[/B]
                    }
                    else
                            System.out.println(number + ".");
                            //JOptionPane.showMessageDialog(null, number + " ");
                }
                number++;
            }
        }
}

**JavaPF** · September 10th, 2009, 04:44 AM

I've used an ArrayList here to store the results and then display them with the JOptionPane.

The JOptionPane is one massive box at the moment. You'll need to figure out how to add a new line after every 10 results or something.

package guiclient;
 
import javax.swing.JOptionPane;
import java.util.ArrayList;
 
public class PrimeNumber
{
    public static void main (String[] args)
        {
 
            [B]ArrayList<String> al = new ArrayList<String>();[/B]
 
            final int Maximum_Primes = 1000;//Number of primes to display
 
            final int Primes_Per_Line = 10; //Display 10 per line
 
            int count = 0;//Count number of prime numbers
 
            int number = 2;
 
            System.out.println("The first 1000 prime numbers are \n");
 
            while (count < Maximum_Primes)
            {
                boolean isPrime = true;
 
                int temp = number/2; // had to declare new variable since you cannot do math in a for loop
 
                for (int divisor = 2;divisor<=temp;divisor++) //you cannot declare divisor 3 times here and it             
 
                                                              //cannot be split on multiple lines 
                {                  
            if (number % divisor == 0){
                                isPrime = false;
                                break;
                        }
                }
                if (isPrime)
                {
                    count++;
                    if (count % Primes_Per_Line != 0)//need to make sure that it will print when its not 
                                                                                            // equal to 0
                    {
 
                System.out.print(number + " ");
               [B] al.add(number + " ");[/B]
 
                    }
                    else
                            System.out.println(number + ".");
                           [B] al.add(number + " ");[/B]
                }
                number++;
            }
 
          [B]JOptionPane.showMessageDialog(null, al);[/B]
 
        }
}

**JavaPF** · September 10th, 2009, 05:28 AM

Your lucky i'm bored today

Try this:

import javax.swing.JOptionPane;
import java.util.ArrayList;
 
public class PrimeNumber
{
    public static void main (String[] args)
        {
 
            ArrayList<String> al = new ArrayList<String>();
            [B]int alCount = 0;[/B]
 
            final int Maximum_Primes = 100;//Number of primes to display
 
            final int Primes_Per_Line = 10; //Display 10 per line
 
            int count = 0;//Count number of prime numbers
 
            int number = 2;
 
            System.out.println("The first 1000 prime numbers are \n");
 
            while (count < Maximum_Primes)
            {
                boolean isPrime = true;
 
                int temp = number/2; // had to declare new variable since you cannot do math in a for loop
 
                for (int divisor = 2;divisor<=temp;divisor++) //you cannot declare divisor 3 times here and it             
 
                                                              //cannot be split on multiple lines 
                {                  
            if (number % divisor == 0){
                                isPrime = false;
                                break;
                        }
                }
                if (isPrime)
                {
                    count++;
                    if (count % Primes_Per_Line != 0)//need to make sure that it will print when its not 
                                                                                            // equal to 0
                    {
 
                System.out.print(number + " ");
 
       [B]         alCount++;
 
                if(alCount == 10){
                    al.add(number + "\n");
                    alCount = 0;
                }else{
                al.add(number + " ");
                }[/B]
 
 
                    }
                    else
                            System.out.println(number + ".");
 
                }
                number++;
            }
 
          JOptionPane.showMessageDialog(null, al);
 
        }
}

**Freaky Chris** · September 10th, 2009, 09:17 AM

lol. JavaPF you make me laugh

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