Question

Summary: I’m currently doing an applet laboratory exercise that simulates a taxi cab, it has to have a display of the speed, fuel, fare and distance traveled, also a marquee whether the cab is occupied or vacant. it has buttons that gives interaction to the user.
Problem: I used a thread for the fare, distance and fuel and another thread for the marquee, but why is it that my marquee blinks continuously?

Answer 1

Without code, it’s really anyone’s guess, but regardless I’ll take a stab. My guess is that you’re drawing directly in the JApplet’s paint(...) method and thereby losing all possible gain from Swing’s double buffering. If so, then change this and draw in the paintComponent(...) method of a JPanel that the JApplet is displaying.

If this doesn’t help, then consider giving us enough information so that we don’t have to guess. You may want to fill us in on how you’re doing your threading and assure us that you’re careful to obey Swing threading rules and update Swing components on the event thread only.

Edit
Your code:

import java.awt.*;
import java.awt.event.ActionEvent;
import javax.swing.JApplet;
import javax.swing.*;
import java.awt.event.ActionListener;
import java.io.*;
import javax.swing.border.Border;
/**
 *
 * @author IC
 */
public class taxiCab extends JApplet implements ActionListener {
    private JTextField speed, distance, fare, fuel, ov, full, tf, tf_fuel, tf_speed;
    private JButton butt, start, butt_pass, butt_sUp, butt_sDown, butt_refuel;
    private JLabel label;
    private JPanel main, north, south, south_left, south_right, center, center_content, north_speed, north_distance, north_fuel, north_fare;
    private Container contain;
    private int speedVal, distanceVal, passval, thread_sleep, status_width, fuel_width;
    private float fuelVal, fareVal;
    private Graphics g;
    private String status;
    private Font font2 = new Font("Kozuka Gothic Pro B", Font.BOLD, 60);
    private Border border2 = BorderFactory.createLineBorder(Color.black, 3);
    private Border border1 = BorderFactory.createLineBorder(Color.black, 1);
    private final int width_ = 500;
    private final int height_ = 300;
    Thread thread1 = new trd1();
    Thread thread2 = new trd2();
    /**
     * Initialization method that will be called after the applet is loaded into
     * the browser.
     */
    public void init() {
        setSize(width_,height_);
        status = new String();
        status = "VACANT";
        status_width = -330;
        Border border3 = BorderFactory.createLineBorder(Color.black, 5);
                thread1 = new trd1();
                thread2.start();
                thread2.suspend();
        contain = new Container();
        contain = getContentPane();
        main = new JPanel(new BorderLayout());
            north = new JPanel(new GridLayout(2,2));
            north.setBackground(Color.blue);
                north_speed = new JPanel();
                    tf_speed = new JTextField(10);
                    tf_speed.setBorder(border1);
                    tf_speed.setText("Speed");
                    tf_speed.setHorizontalAlignment(JTextField.CENTER);
                    tf_speed.setBackground(Color.CYAN);
                    tf_speed.setEditable(false);
                    speed = new JTextField(10);
                    speed.setBorder(border1);
                    speed.setEditable(false);
                    speed.setText("-");
                    speed.setHorizontalAlignment(JTextField.CENTER);
                    north_speed.add(tf_speed);
                    north_speed.add(speed);
                north_distance = new JPanel();
                    tf = new JTextField(10);
                    tf.setBorder(border1);
                    tf.setText("Distance");
                    tf.setHorizontalAlignment(JTextField.CENTER);
                    tf.setBackground(Color.CYAN);
                    tf.setEditable(false);
                    distance = new JTextField(10);
                    distance.setBorder(border1);
                    distance.setEditable(false);
                    distance.setText("-");//<----------------------------------distance
                    distance.setHorizontalAlignment(JTextField.CENTER);
                    north_distance.add(tf);
                    north_distance.add(distance);
                north_fuel = new JPanel();
                    tf_fuel = new JTextField(10);
                    tf_fuel.setBorder(border1);
                    tf_fuel.setText("Fuel");
                    tf_fuel.setHorizontalAlignment(JTextField.CENTER);
                    tf_fuel.setBackground(Color.CYAN);
                    tf_fuel.setEditable(false);
                    fuel = new JTextField(10);
                    fuel.setBorder(border1);
                    fuel.setEditable(false);
                    fuel.setText("-");
                    fuel.setHorizontalAlignment(JTextField.CENTER);
                    north_fuel.add(tf_fuel);
                    north_fuel.add(fuel);
                north_fare = new JPanel();
                    tf = new JTextField(10);
                    tf.setBorder(border1);
                    tf.setText("Fare");
                    tf.setHorizontalAlignment(JTextField.CENTER);
                    tf.setBackground(Color.CYAN);
                    tf.setEditable(false);
                    fare = new JTextField(10);
                    fare.setBorder(border1);
                    fare.setEditable(false);
                    fare.setText("-");
                    fare.setHorizontalAlignment(JTextField.CENTER);
                    north_fare.add(tf);
                    north_fare.add(fare);
                north.add(north_speed);
                north.add(north_distance);
                north.add(north_fuel);
                north.add(north_fare);
            center = new JPanel(new BorderLayout(3,3));
                center_content = new JPanel(new GridLayout(2,1,0,15));
                    ov = new JTextField(20);
                    ov.setText("");
                    ov.setBackground(Color.yellow);
                    ov.setEditable(false);
                    ov.setBorder(border2);
                    full = new JTextField(20);
                    full.setHorizontalAlignment(JTextField.CENTER);
                    full.setText("FUELMeter");
                    full.setIgnoreRepaint(true);
                    full.setFont(font2);
                    full.setBorder(border2);
                    center_content.add(ov);
                    center_content.add(full);
                center.add(center_content, "Center");
                center_content.setBackground(Color.yellow);
                label = new JLabel("   ");
                center.add(label, "North");
                label = new JLabel("   ");
                center.add(label, "West");
                label = new JLabel("   ");
                center.add(label, "South");
                label = new JLabel("   ");
                center.add(label, "East");
            south = new JPanel(new BorderLayout());
                south_left = new JPanel(new GridLayout(2,1));
                    butt_sUp = new JButton("Speed Up");
                    butt_sUp.setBorder(border1);
                    butt_sUp.addActionListener(this);
                    butt_sUp.setEnabled(false);
                    south_left.add(butt_sUp);
                    butt_sDown = new JButton("Speed Down");
                    butt_sDown.setBorder(border1);
                    butt_sDown.addActionListener(this);
                    butt_sDown.setEnabled(false);
                    south_left.add(butt_sDown);
                south_right = new JPanel(new GridLayout(2,1));
                    butt_pass = new JButton("Passenger In");
                    butt_pass.setBorder(border1);
                    butt_pass.addActionListener(this);
                    butt_pass.setEnabled(false);
                    south_right.add(butt_pass);
                    butt_refuel = new JButton("Refuel");
                    butt_refuel.setBorder(border1);
                    butt_refuel.addActionListener(this);
                    butt_refuel.setEnabled(false);
                    south_right.add(butt_refuel);
                butt = new JButton("Start");
                butt.setBorder(border1);
                    butt.addActionListener(this);
                south.add(butt, "Center");
                south.add(south_left, "West");
                south.add(south_right, "East");
        north.setBorder(border1);
        center.setBorder(border1);
        south.setBorder(border1);
        center.setBackground(Color.yellow);
        main.add(north, "North");
        main.add(center, "Center");
        main.add(south, "South");
        main.setBorder(border1);
        //main.setIgnoreRepaint(true);
        contain.add(main);
        contain.setVisible(true);
        //contain.setIgnoreRepaint(true);


    }
    public void paint(Graphics g){
        super.paint(g);
        g.setColor(Color.black);
        g.setFont(font2);
        g.drawString(status, status_width, 140);
        g.setColor(Color.yellow);
        g.fillRect(2,82,12,70);
        g.fillRect(getWidth()-14,82,12,70);
        g.setColor(Color.black);
        g.fillRect(0,82,2,70);
        g.setColor(Color.GREEN);
        g.fillRect(17,(getHeight()/2)+20,fuel_width,getHeight()-(83+(getHeight()/2)));
        main.setBorder(border1);
    }

    public void actionPerformed(ActionEvent e) {
        if(e.getActionCommand() == "Start"){
            butt.setLabel("Stop");
            butt_pass.setEnabled(true);
            fuelVal =  50.00f;
            distanceVal = 0;
            fareVal = 40.00f;
            speedVal = 0;
            fuel.setText(String.valueOf(fuelVal) + " L");
            distance.setText(String.valueOf(distanceVal) + " km");
            fare.setText("Php " + String.valueOf(fareVal));
            speed.setText(String.valueOf(speedVal) + " kph");
                thread1 = new trd1();
                thread1.start();
                thread2 = new trd2();
                thread2.start();
            //BufferedWriter bw;<-----------------------------------------------
            }
        else if(e.getActionCommand() == "Stop"){
            butt.setLabel("Start");
            butt_pass.setEnabled(false);
            butt_sUp.setEnabled(false);
            butt_sDown.setEnabled(false);
            butt_refuel.setEnabled(false);
            butt_pass.setLabel("Passenger In");

            thread1.stop();
        }
        else if(e.getActionCommand() == "Speed Up"){
            if(speedVal == 0){
                speedVal+=25;
                speed.setText(String.valueOf(speedVal) + " kph");
                butt_sDown.setEnabled(true);
                tf_speed.setText("Speed");
                thread1 = new trd1();
                thread1.start();
            }
            else if(speedVal == 275){
                speedVal+=25;
                speed.setText(String.valueOf(speedVal) + " kph");
                //butt_sUp.setEnabled(false);
                tf_speed.setText("MAX SPEED");
            }
            else{
                speedVal+=25;
                speed.setText(String.valueOf(speedVal) + " kph");
                }
        }
        else if(e.getActionCommand() == "Speed Down"){
            repaint();
            if(speedVal==25){
                speedVal-=25;
                speed.setText(String.valueOf(speedVal) + " kph");
                tf_speed.setText("S T O P P E D");
                butt_sDown.setEnabled(false);
            }
            else if(speedVal == 300){
                speedVal-=25;
                speed.setText(String.valueOf(speedVal) + " kph");
                tf_speed.setText("Speed");
                butt_sUp.setEnabled(true);
            }
            else{
                speedVal-=25;
                speed.setText(String.valueOf(speedVal) + " kph");
            }
        }
        else if(e.getActionCommand() == "Passenger In"){
            butt_pass.setLabel("Passenger Out");
            fareVal = 40.0f;
            fare.setText("Php " + String.valueOf(fareVal));
            butt_sUp.setEnabled(true);
            butt_sDown.setEnabled(true);
            butt_refuel.setEnabled(true);
            speedVal = 25;
            speed.setText(String.valueOf(speedVal) + " kph");
            status = "OCCUPIED";
                thread1 = new trd1();
                thread1.start();


        }
        else if(e.getActionCommand() == "Passenger Out"){
            status = "VACANT";
            butt_pass.setLabel("Passenger In");
            thread1.stop();
        }
        else if(e.getActionCommand() == "Refuel"){
            if(fuelVal == 0.0f){
                fuelVal = 50.00f;
                fuel.setText(String.valueOf(fuelVal));
                tf_fuel.setBackground(Color.cyan);
                tf_fuel.setText("Fuel");
                        fuel_width = (int)((getWidth()-34)*fuelVal/50f);
                thread1 = new trd1();
                thread1.start();
            }
            else{
                fuelVal = 50.00f;
                fuel.setText(String.valueOf(fuelVal) + " L");
            }
        }
    }

    public class trd1 extends Thread implements Runnable {

        public void run(){
            if(fuelVal>0.00f || speedVal>0){
                for(;;){
                    try {
                        Thread.sleep(50000/speedVal);
                        if(fuelVal == 0.00f || speedVal == 0)
                            thread1.stop();
                        distanceVal++;
                        fareVal += 1.00;
                        fuelVal -=.25f;
                        fuel_width = (int)((getWidth()-34)*fuelVal/50f);
                        repaint();
                        distance.setText(String.valueOf(distanceVal)+" km");
                        fuel.setText(String.valueOf(fuelVal)+" L");
                        fare.setText("P " + String.valueOf(fareVal));
                    } catch (InterruptedException e) {
                    }
                }
            }
            }
        }
    public class trd2 extends Thread implements Runnable {
        //tf_fuel = new JTextField(15);

        public void run(){
                for(int b = 0;;b++){
                    try {
                        Thread.sleep(10);
                        status_width +=1;
                        if(status_width == getWidth())
                            status_width = -330;
                        repaint();
                        if(fuelVal == 0.0f){
                            if(b%2==0){
                                tf_fuel.setBackground(Color.red);
                                tf_fuel.setText("R E F U E L");
                                }
                            else{
                                tf_fuel.setBackground(Color.cyan);
                                tf_fuel.setText("R E F U E L");
                                }
                        }
                    } catch (InterruptedException e) {
                    }
                }


        }
    }
}

Yep, I guessed correctly: you’re painting directly in the JApplet. As I stated initially, don’t do that. In fact your best bet at learning to do this correctly is to read the tutorials:

• Lesson: Performing Custom Painting (the basics)
• Painting in AWT and Swing (for more advanced concepts)

You’ve also got a lot of other errors in your code, some significant, including using == to compare Strings rather than the equals(...) or equalsIgnoreCase(...) method, and trying to call Thread#stop() directly. Never do that. Also don’t set a component’s border within paint or paintComponent. Also you are setting a component’s text and background color from within a background thread and off of the Swing event thread — two potential causes of intermittent and hard to debug threading errors. You’ll only want to do these things on the Swing event thread.