Prime Number Help

I'm working on a homework assignment with the following requirement:

Quote:

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Write a Java program that meets the following requirements:

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 61 73 79 83 89 97 … …


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

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Here is what I have so far:

Code:

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import javax.swing.JOptionPane;

public class PrimeNumber {

        public static boolean isPrime(int num) {
                if (num <  2) return false;
                if (num == 2) return true;
                int n = (int) Math.sqrt(num);
                for (int i = 3; i < n; i += 2) {
                        if (num%i == 0) return false;
                }
                return true;
}
        public void main(String[] args) {
                int[] primes = new int[1000];       
                primes[0] = 2;                               
                int count = 1;
                int num = 3;
                // Find the first 1000 primes
                while (count<1000) {
                        if (isPrime(num)) {
                                primes[count] = num;
                                count++;
                        }
                        num = num + 2;
                }
                String output = (primes[i] + "\t");
                               
                        // Display the result
                JOptionPane.showMessageDialog(null, output,
                        "Assignment 5.1 Output", JOptionPane.INFORMATION_MESSAGE);
               
                System.exit(0);
        }
}

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I keep getting this error in JCreator Lite:

Quote:

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C:\Users\Craig\Documents\Downloads\PrimeNumber.java:57: cannot find symbol
symbol : variable i
location: class PrimeNumber
.........String output = (primes[i] + "\t");
........................................^
1 error

Process completed.

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What am I doing wrong? Everything else seems to be going okay and the examples I was given in my course seem to line up.

Thanks for any help!

I've made the following updates:

Code:

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import javax.swing.JOptionPane;

public class PrimeNumber {
        // Main Method
        public static boolean isPrime(int num) {
               
                int[] numbers = new int[0];
                // Reads an input number
                for (int i = 0; i < numbers.length; i++) {
                        String numString = JOptionPane.showInputDialog(null,
                        "Enter a number: ",
                        "Assignment 5.1 Input", JOptionPane.QUESTION_MESSAGE);
                       
                // Convert string into integer
                numbers[i] = Integer.parseInt(numString);               
                }
                // Determines primes
                if (num <  2) return false;
                if (num == 2) return true;
                int n = (int) Math.sqrt(num);
                for (int i = 3; i < n; i += 2) {
                        if (num&#37;i == 0) return false;
                }
                return true;
        }
        public void main(String[] args) {
                //Declares "primes" as my variable
                int[] primes = new int[1000];       
                primes[0] = 2;                               
                int count = 1;
                int num = 3;
                // Finds the first 1000 primes
                while (count<1000) {
                        if (isPrime(num)) {
                                primes[count] = num;
                                count++;
                        }
                        num = num + 2;
                }
                // Prepares the output
                String output = "The first 1000 primes are: ";
                for (int i=0; i<primes.length; i++)
               
                output += primes[i] + "\t";
                               
                        // Display the result
                JOptionPane.showMessageDialog(null, output,
                        "Assignment 5.1 Output", JOptionPane.INFORMATION_MESSAGE);
               
                System.exit(0);
        }
}

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It shows as building properly, but before it runs I get this error:

Quote:

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--------------------Configuration: <Default>--------------------
java.lang.NoSuchMethodError: main
Exception in thread "main"
Process completed.

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???

Here is the latest version. I just can't seem to get the columns to work right.

Code:

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import javax.swing.JOptionPane;

public class PrimeNumberTest {       
               
                // Check if an integer is a prime
        public static boolean isPrime(int num) {
                if (num <  2) return false;
                if (num == 2) return true;
                int n = (int) Math.sqrt(num);
                for (int i=3; i<n; i+=2) {
                        if (num&#37;i == 0) return false;
                }
                return true;
        }
        // Main Method
        public static void main(String[] args) {
                int[] primes = new int[1000];        // Define the array of the first 1000 primes
                primes[0] = 2;                                        // The smallest prime is 2;
                int count = 1;
                int num = 3;
                // Find the first 1000 primes
                while (count<1000) {
                        if (isPrime(num)) {
                                primes[count] = num;
                                count++;
                        }
                        num = num + 2;
                }
                // Opens the Welcome Message
                JOptionPane.showMessageDialog(null, "Click OK to see all prime numbers under 10000",
                "Assignment 5.1", JOptionPane.INFORMATION_MESSAGE);
               
                // Prepares the output
                String output = "The first 1000 primes are: ";
                for (int i=0; i<primes.length; i++)        {
                //        if (i%10 == 0), primes[i] ("");
                        output += primes[i] + "\n";}
                               
                        // Display the result
                JOptionPane.showMessageDialog(null, output,
                        "Assignment 5.1 Output", JOptionPane.INFORMATION_MESSAGE);
               
                System.exit(0);
        }
}

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Have a look in the math forum! There might be a java example for prime numbers in there.