JOptionPane problem

oracle.com isnt being of any help to me at this point. heres my error

Code :

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client.java:18: cannot find symbol
symbol  : variable frame
location: class client
                JOptionPane.showMessageDialog(frame, "testing", "testing");
                                              ^
1 error
Finished!
Press any key to continue . . .

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heres my code

Code :

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import java.lang.Object.*;
import javax.swing.*;
 
public class client  {
 
public static int message = 0;
 
public static int random(int range) {
        return (int) (Math.random() * (range + 1));
    }
 
	public static void main(String[] args) {
		Message();
		JOptionPane.showMessageDialog(frame, "testing", "testing");
	}
 
	public static void Message() {
		message = random(4);
			if (message == 0) {
				System.out.println("");
			} else if (message == 1) {
				System.out.println("");
			} else if (message == 2) {
				System.out.println("");
			} else if (message == 3) {
				System.out.println("");
			} else if (message == 4) {
				System.out.println("");
		}
	}
}

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The issue is very clear, Cannot find 'frame', you haven't declared anything called frame anywhere.
If you just replace 'frame' with null, it will use a default frame for you.

A classic example of copying code without understanding it.