clear Jpanel before next time drawing

Question

I've created an analogclock were u can type a digital time and the program draws a clock that shows the time and updates it self secondly. But at every update the old lines still remain. the variables are named german but i don't think thats that much of an issue.

Code for GUI:

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
/**
 *
 * @author user
 */
public class Uhr extends javax.swing.JFrame implements ActionListener {

    /**
     * Creates new form Uhr
     */
    public Uhr() {
        initComponents();
        
    }

    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        jButton1 = new javax.swing.JButton();
        panel = new javax.swing.JPanel();
        ueberschrift = new javax.swing.JLabel();
        eingabe = new javax.swing.JTextField();
        eingabe_label = new javax.swing.JLabel();
        button = new javax.swing.JButton();
        label = new javax.swing.JLabel();

        jButton1.setText("jButton1");

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setCursor(new java.awt.Cursor(java.awt.Cursor.DEFAULT_CURSOR));
        setName("Uhr"); // NOI18N

        javax.swing.GroupLayout panelLayout = new javax.swing.GroupLayout(panel);
        panel.setLayout(panelLayout);
        panelLayout.setHorizontalGroup(
            panelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 220, Short.MAX_VALUE)
        );
        panelLayout.setVerticalGroup(
            panelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 220, Short.MAX_VALUE)
        );

        ueberschrift.setFont(new java.awt.Font("MS Reference Sans Serif", 0, 18)); // NOI18N
        ueberschrift.setHorizontalAlignment(javax.swing.SwingConstants.CENTER);
        ueberschrift.setText("Analoguhr");

        eingabe.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                eingabeActionPerformed(evt);
            }
        });

        eingabe_label.setFont(new java.awt.Font("MS Reference Sans Serif", 0, 12)); // NOI18N
        eingabe_label.setText("Uhrzeit:");

        button.setText("Uhr zeichnen");
        button.setCursor(new java.awt.Cursor(java.awt.Cursor.HAND_CURSOR));
        button.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                buttonActionPerformed(evt);
            }
        });

        label.setFont(new java.awt.Font("MS Reference Sans Serif", 0, 24)); // NOI18N
        label.setHorizontalAlignment(javax.swing.SwingConstants.CENTER);

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
                        .addComponent(eingabe)
                        .addComponent(eingabe_label, javax.swing.GroupLayout.PREFERRED_SIZE, 105, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addComponent(button, javax.swing.GroupLayout.DEFAULT_SIZE, 161, Short.MAX_VALUE))
                    .addComponent(label, javax.swing.GroupLayout.PREFERRED_SIZE, 161, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 49, Short.MAX_VALUE)
                .addComponent(panel, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
            .addGroup(layout.createSequentialGroup()
                .addGap(98, 98, 98)
                .addComponent(ueberschrift, javax.swing.GroupLayout.PREFERRED_SIZE, 220, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                .addGap(18, 18, 18)
                .addComponent(ueberschrift, javax.swing.GroupLayout.DEFAULT_SIZE, 45, Short.MAX_VALUE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createSequentialGroup()
                        .addComponent(eingabe_label, javax.swing.GroupLayout.PREFERRED_SIZE, 27, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                        .addComponent(eingabe, javax.swing.GroupLayout.PREFERRED_SIZE, 31, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                        .addComponent(button)
                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                        .addComponent(label, javax.swing.GroupLayout.PREFERRED_SIZE, 39, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addGap(83, 83, 83))
                    .addComponent(panel, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)))
        );

        pack();
    }// </editor-fold>                        

    public void uhr_paint() {
        Graphics2D leinwand = (Graphics2D) panel.getGraphics();
        leinwand.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        leinwand.setColor(Color.BLACK);
        leinwand.drawOval(10, 10, 200, 200);
    }

    public void zifferblatt() {

        Graphics2D leinwand = (Graphics2D) panel.getGraphics();
        leinwand.setStroke(new BasicStroke(10));
        leinwand.setColor(Color.BLACK);
        double winkel;
        int zifferblatt_x, zifferblatt_y;
        int radius = 85;
        for (int i = 1; i <= 12; i++) {
            winkel = i * Math.PI / 6;
            zifferblatt_x = (int) (radius * Math.sin(winkel));
            zifferblatt_y = (int) (radius * Math.cos(winkel));
            leinwand.drawString(Integer.toString(i), 110 + zifferblatt_x, 110 - zifferblatt_y);
        }
    }

    
    
    private void eingabeActionPerformed(java.awt.event.ActionEvent evt) {                                        
    }                                       

    private void buttonActionPerformed(java.awt.event.ActionEvent evt) {                                       
        Zeit.zeit();
        uhr_paint();
        zifferblatt();
        Timer.timer();
    }                                      

    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(Uhr.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(Uhr.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(Uhr.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(Uhr.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new Uhr().setVisible(true);
                
            }
        });
    }

    // Variables declaration - do not modify                     
    public static javax.swing.JButton button;
    public static javax.swing.JTextField eingabe;
    private javax.swing.JLabel eingabe_label;
    private javax.swing.JButton jButton1;
    public static javax.swing.JLabel label;
    public static javax.swing.JPanel panel;
    private javax.swing.JLabel ueberschrift;
    // End of variables declaration                   

    @Override
    public void actionPerformed(ActionEvent e) {
        throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
    }
}

Code to get the time:

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
/**
 *
 * @author user
 * die Eingabe in Integer umwandeln
 */
public class Zeit {

    public static int stundenzeit, minutenzeit, sekundenzeit,
            stunde_x, stunde_y, minute_x, minute_y, sekunde_x, sekunde_y;
    public static String uhrzeit;

    public static void zeit() {
        try {

            uhrzeit = Uhr.eingabe.getText();
            String[] uhrzeit_split = uhrzeit.split(":");

            String stundenzeit_string = uhrzeit_split[0];
            String minutenzeit_string = uhrzeit_split[1];
            String sekundenzeit_string = uhrzeit_split[2];

            stundenzeit = Integer.parseInt(stundenzeit_string);
            minutenzeit = Integer.parseInt(minutenzeit_string);
            sekundenzeit = Integer.parseInt(sekundenzeit_string);

            if (stundenzeit < 1 | sekundenzeit > 12
                    | minutenzeit < 0 | minutenzeit > 59
                    | sekundenzeit < 0 | sekundenzeit > 59) {
                System.err.println("Bitte schreibe ein Uhrzeit!");
            }
        } catch (NumberFormatException e) {
            System.err.println("Bitte schreibe ein Uhrzeit!");
        }
    }
}

Clock hands:

import java.awt.BasicStroke;
import java.awt.Color;
import static java.awt.Color.black;
import static java.awt.Color.red;
import java.awt.Graphics2D;
import java.awt.RenderingHints;

/**
 *
 * @author user Die Zeiger berechnen und zeichnen
 */
public class Zeiger {

    public static int Stunde_x, Stunde_y, Minute_x, Minute_y, Sekunde_x, Sekunde_y;

    public static int stundenzeit_x(int Zeigerlänge, int radiusUhr) {

        Stunde_x = (int) ((int) Zeigerlänge * Math.sin(Math.toRadians(((12 - Timer.stundenzeit_update) * 30) - 180 - (Timer.minutenzeit_update / 2))) + radiusUhr);
        return Stunde_x;
    }

    public static int stundenzeit_y(int Zeigerlänge, int radiusUhr) {

        Stunde_y = (int) ((int) Zeigerlänge * Math.cos(Math.toRadians(((12 - Timer.stundenzeit_update) * 30) - 180 - (Timer.minutenzeit_update / 2))) + radiusUhr);
        return Stunde_y;
    }

    public static int minutenzeit_x(int Zeigerlänge, int radiusUhr) {

        Minute_x = (int) (Zeigerlänge * Math.sin(Math.toRadians(((60 - Timer.minutenzeit_update) * 6) - 180)) + radiusUhr);
        return Minute_x;
    }

    public static int minutenzeit_y(int Zeigerlänge, int radiusUhr) {

        Minute_y = (int) (Zeigerlänge * Math.cos(Math.toRadians(((60 - Timer.minutenzeit_update) * 6) - 180)) + radiusUhr);
        return Minute_y;
    }

    public static int sekundenzeit_x(int Zeigerlänge, int radiusUhr) {
        
        Sekunde_x = (int) (Zeigerlänge * Math.sin(Math.toRadians(((60 - Timer.sekundenzeit_update) * 6) - 180)) + radiusUhr);
        return Sekunde_x;
    }

    public static int sekundenzeit_y(int Zeigerlänge, int radiusUhr) {
        Sekunde_y = (int) (Zeigerlänge * Math.cos(Math.toRadians(((60 - Timer.sekundenzeit_update) * 6) - 180)) + radiusUhr);
        return Sekunde_y;
    }

    public static void stundenzeiger_paint() {
        Graphics2D leinwand = (Graphics2D) Uhr.panel.getGraphics();
        int radiusUhr = 110;
        stundenzeit_x(40, radiusUhr);
        stundenzeit_y(40, radiusUhr);
        leinwand.setStroke(new BasicStroke((float) 1.5));
        leinwand.setColor(black);
        leinwand.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        leinwand.drawLine(110, 110, Stunde_x, Stunde_y);
    }

    public static void minutenzeiger_paint() {
        Graphics2D leinwand = (Graphics2D) Uhr.panel.getGraphics();
        int radiusUhr = 110;
        minutenzeit_x(70, radiusUhr);
        minutenzeit_y(70, radiusUhr);
        leinwand.setStroke(new BasicStroke((float) 1.25));
        leinwand.setColor(Color.BLUE);
        leinwand.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        leinwand.drawLine(110, 110, Minute_x, Minute_y);
    }

    public static synchronized void sekundenzeiger_paint() {
        Graphics2D leinwand = (Graphics2D) Uhr.panel.getGraphics();
        int radiusUhr = 110;
        sekundenzeit_x(80, radiusUhr);
        sekundenzeit_y(80, radiusUhr);
        leinwand.setStroke(new BasicStroke(1));
        leinwand.setColor(red);
        leinwand.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        leinwand.drawLine(110, 110, Sekunde_x, Sekunde_y);
    }
}

And finally the timer:

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

/**
 *
 * @author user 
 * Sekuendliches aktualisieren des Timer-labels und der Uhr
 */
public class Timer {

    static int sekundenzeit_update = Zeit.sekundenzeit,
            minutenzeit_update = Zeit.minutenzeit,
            stundenzeit_update = Zeit.stundenzeit;

    static String uhrzeit_update = Zeit.stundenzeit + ":"
            + Zeit.minutenzeit + ":" + Zeit.sekundenzeit;

    public static void timer() {
        Runnable helloRunnable;
        helloRunnable = () -> {

            Uhr.label.setText("");
            Uhr.label.setText(uhrzeit_update);
            timer_ausführen();
            Zeiger.stundenzeiger_paint();
            Zeiger.minutenzeiger_paint();
            Zeiger.sekundenzeiger_paint();

        };
        ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);
        executor.scheduleAtFixedRate(helloRunnable, 0, 1, TimeUnit.SECONDS);
    }

    public static void timer_ausführen() {

        sekundenzeit_update += 1;

        if (sekundenzeit_update > 60) {
            sekundenzeit_update = 0;
            minutenzeit_update += 1;

            if (minutenzeit_update > 60) {
                minutenzeit_update = 0;
                stundenzeit_update += 1;
            }
        }
        uhrzeit_update = stundenzeit_update + ":" + minutenzeit_update
                + ":" + sekundenzeit_update;

    }
}

clock in the beginning: https://i.stack.imgur.com/Nf5Hu.png

clock after one minute

I did this with Netbeans and I had the idea to draw this by hand but I really dont know how to do this.

Answer 1

This is not the way Swing JComponents are supposed to be used. You are supposed to create a subclass (of JPanel in your case) and in the subclass override paintComponent, which should be made to always paint the correct time whenever it is called. Then you can use a javax.swing.Timer to call repaint every second.

Sie sollen Swing in ein anderes weg nutzen. Sie mussen JPanel "Subclassen", und dann diese funktion "paintComponent" uberritten :)