Java licensing system URGENT

Hello, Sorry to bother you busy people :cool:

I've got a client i dont trust will pay me after a week of testing the program i have developed.

Could somebody direct me as to where i could go for a tutorial or a way of going to create a demo license for this program, After a week it will stop working. Then i will give him the full version..

Need this urgent have to meet client in 3 hours.

Don't give me code just point me in the right direction, This will come handy in my future programs :D

nobody culd help so i did a dodgy trial system for now..

Code :

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import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Scanner;
 
import javax.swing.JOptionPane;
 
 
public class license {
 
	public static boolean Expired;
 
	public license() throws Exception{
 
		FileReader file;
		try {
			file = new FileReader("AD Converter/temp/comp.txt");
			Scanner scan = new Scanner(file);
 
		    String licno = scan.next();
		    Integer.parseInt(licno);
 
		    int tempOut = Integer.parseInt(licno);
		    tempOut = tempOut - 1;
 
 
		    if(Integer.parseInt(licno) <= 0){
		    	JOptionPane.showMessageDialog(null, "Sorry, Your trial has expired. Please purchase the product for unlimited use!");
		    	Expired = true;
		    }
		    else if(Integer.parseInt(licno) <= 40){
		    	JOptionPane.showMessageDialog(null, "You current have: " + licno + " uses left.");
		    	PrintWriter out = new PrintWriter(new FileWriter("AD Converter/temp/comp.txt"));
		    	System.out.println(tempOut + " Value");
		    	out.print(tempOut);
		    	Expired = false;
		    	out.close();
		    }
 
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
 
	}
 
}

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