CODEWITHSUNDEEP
java
Emmaline Smith
Emmaline Smith

Reputation: 51

Java Moving an Object Across the Screen

I am trying to move a train across my java window and am having serious problems. I have a Train class in which I made the train, and a Driver class which is supposed to move the train. I need to make the whole train move from right to left until it 'passes' the left edge of the screen. Then add an if statement to change the dx so the train restarts on the right side . The below is what I have tried but it is not working. Can anyone help me please??

public class Driver extends GraphicsProgram
{
    //~ Instance/static variables .............................................

    private static final int N_STEPS = 1000;
    private static final int PAUSE_TIME = 20;
    private static final double TRAIN_LENGTH = 320;

    //~ Constructor ...........................................................

    // ----------------------------------------------------------
    /**
     * The run() method of the Driver Class.
     * Creates an instance of the Train Class.
     * Responsible for animating the train across the screen.
     */
    public void run()
    {
        Train train = new Train(getGCanvas());
        for (int i = 0; i < N_STEPS; i++) {
            train.move(-100, 0);
            pause(PAUSE_TIME);
    }

Upvotes: 4

Views: 69986

Answers (2)

Mars
Mars

Reputation: 1

color c = color(0); float x = 0; float y = 100; float speed = 1;
void setup() { size(200,200); }
void draw() { background(255); move(); display(); }
void move() { x = x + speed; if (x > width) { x = 0; } }
void display() { fill(c); rect(x,y,30,10); }

Upvotes: -1

Aurelien Ribon
Aurelien Ribon

Reputation: 7634

Here is a little demo made with swing. Just replace the black rectangle with an image of your train and you're done.

The trick is to use a separate thread (or timer) to do the animation loop (often called game loop). The loop only tells your window to redraw itself, and on each redraw, you first compute the new positions of the animated objects, then you draw them.

import javax.swing.*;
import java.awt.*;

public class TrainDemo {

    public static void main(String[] args) {
        JFrame frame = new JFrame("Train Demo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(800, 400);
        frame.setLocationRelativeTo(null);
        frame.add(new TrainCanvas());
        frame.setVisible(true);
    }

}

class TrainCanvas extends JComponent {

    private int lastX = 0;

    public TrainCanvas() {
        Thread animationThread = new Thread(new Runnable() {
            public void run() {
                while (true) {
                    repaint();
                    try {Thread.sleep(10);} catch (Exception ex) {}
                }
            }
        });

        animationThread.start();
    }

    public void paintComponent(Graphics g) {
        Graphics2D gg = (Graphics2D) g;

        int w = getWidth();
        int h = getHeight();

        int trainW = 100;
        int trainH = 10;
        int trainSpeed = 3;

        int x = lastX + trainSpeed;

        if (x > w + trainW) {
            x = -trainW;
        }

        gg.setColor(Color.BLACK);
        gg.fillRect(x, h/2 + trainH, trainW, trainH);

        lastX = x;
    }

}

Upvotes: 3

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