// Prime.java
//
// input: natural number n
// output: smallest prime number p with p > n
//
// method: apply prime test to n+1, n+2, ... until prime is found,
//         prime testing of z is done by testing numbers k = 2 ...  with
//         k * k <= z if they are factors of z
//

import java.awt.*;
import java.applet.Applet;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class Prime extends Applet {
        Label inputPrompt;        // declare Label
        TextField input, output;  // declare textfields for input and output

        int n,        // the input integer read from terminal
            z,        // candidate for the prime, set to n+1, n+2 etc.
            k;        // possible divisor of z
        boolean  divisorFound;     // Boolean, indicates that a divisor
                                   // k of z has been found

        // setup the graphical user interface components
        // and initialize labels and text fields
        public void init() {
                // set layout
                setLayout(new FlowLayout( FlowLayout.LEFT));
                // set Font
                Font myFont = new Font("Times", Font.PLAIN, 18);
                setFont(myFont);
                setSize(800, 100);

                inputPrompt = new Label("Geben Sie die Zahl n ein "
                        + "und druecken Sie Return.");
                input = new TextField(10);
                input.addActionListener(new ActionListener() {
                        public void actionPerformed(ActionEvent e) {
                                // call method for finding next prime

                                String str = "Die naechstgroessere Primzahl nach "
                                 + n + " ist " + findPrime(Integer.parseInt(input.getText())) + '.';

                // put the sting into the output field
                output.setText( str );
                        }
                });    // action will be on input field

                // output will be text in a field
                output = new TextField(60);
                output.setEditable(false);
                output.setBackground(Color.yellow);

                add(inputPrompt);    // put prompt on applet
                add(input);          // put input on applet
                add(output);         // put output on applet
        }

        // function for finding next prime number
        public int findPrime(int param) {
                // get input number
                n = param;
                z = n;
                do {
                        z++;
                        k = 2;
                        divisorFound = false;
                                // so far no divisor of z has been found
                        while ((!divisorFound) && (k*k <= z)) {
                                // check if k is a divisor of z
                                if (z % k == 0) {
                                        divisorFound = true;
                                }
                                k++;
                        } //end while
                } while (divisorFound);
                return z;
                // define the output string

        }
}