How to change an Image in JFrame when a timer reaches a number?

Question

as the title says, im trying to change an image in a jframe using a timer. but it throws a NullPointerException. I am pretty new at java, and while i am in the process of researching exception handling, any direction you can give me will help my learning greatly. here is my code:

public class PointTest extends JPanel {
    JLabel drawcloseLabel = new JLabel(new ImageIcon("src/images/draw_closeup.jpg"));
    JLabel monsterAttack = new JLabel("src/images/monsterAttack.jpg");
    JLabel endGameLabel = new JLabel(new ImageIcon("src/images/monsterAttack.jpg"));
    private static final long serialVersionUID = 1L; // i dont get this
    private JFrame frame;

    boolean off = false;
    public JButton opendraw;
    // public JButton button2;
    public JButton ok;
    public JButton back;
    public JButton pickUpKey;
    public JButton Key;
    public JButton unlockDoor;
    public JButton lockedDoor;

    public JButton btnNewButton;
    JPanel background;
    JPanel door;
    JPanel draw;
    JPanel drawopen;
    JPanel endGame;

    public void room() {

        frame = new JFrame("room");


        frame.setSize(1280, 960);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JLayeredPane layeredPane = new JLayeredPane();
        frame.getContentPane().add(layeredPane, BorderLayout.CENTER);

        background = new JPanel();



endGame = new JPanel();
    JLabel endGameLabel = new JLabel(new ImageIcon("src/images`/OutOfTime.jpg"));`
    JLabel picLabel = new JLabel(new ImageIcon("src/images/room.jpg"));


        background.add(picLabel);

        endGame.add(endGameLabel);

        background.setBounds(0, 0, 1280, 960);


        layeredPane.add(background, JLayeredPane.DEFAULT_LAYER);


    }

this is the method that, if i catch the exception, will continue the countdown to 0, but will not change the image.

         public void EndTimer() {

        //error
        background.setVisible(false);

        endGame.setVisible(true);
        endGame.add(endGameLabel);
        endGame.setBounds(0, 0, 1280, 960);




    }

}

the countdown class for the Timer.

import java.util.Timer;
import java.util.TimerTask;

public class Countdown {
    static int interval;
    static Timer timer;
    boolean off;
    PointTest pt = new PointTest();

    public void Countdown1() {

        int seconds = 10;
        int delay = 1000;
        int period = 1000;
        timer = new Timer();

        interval = seconds;

        timer.scheduleAtFixedRate(new TimerTask() {

            public void run() {
                System.out.println(setInterval());
                if (interval == 7) {
                    System.out.println("works");

                    pt.EndTimer();

                }

            }
        }, delay, period);
    }

    private int setInterval() {
        if (interval == 1)
            timer.cancel();
        return --interval;

    }

    public int getInterval() {

        return this.setInterval();
    }

}



import java.io.IOException;



public class windowMain {


    /**
     * Launch the application.
     * 
     */


    public static void main(String[] args) throws IOException {


        Countdown cd = new Countdown();
        cd.Countdown1();
        PointTest point = new PointTest();
        point.room();




    }

}

Stacktrace:

Exception in thread "Timer-0" works
test
java.lang.NullPointerException
    at PointTest.EndTimer(PointTest.java:207)
    at Countdown$1.run(Countdown.java:27)
    at java.util.TimerThread.mainLoop(Unknown Source)
    at java.util.TimerThread.run(Unknown Source)

The stack trace of the exception is first you should analyse/post here. — Würgspaß, Jan 20 '16 at 12:58
were the try catch is, any of those lines, i delete one, then the exception becomes the next line, e.g, i delete background.setVisible(false) and endGame.setVisible(true) becomes the exception — noobAlert, Jan 20 '16 at 13:01
@noobAlert less code, more stack trace. Stack trace is the error message output in all its beauty after the exception occurred and crashed your program. — Würgspaß, Jan 20 '16 at 13:06
1) For better help sooner, post a [MCVE] or [Short, Self Contained, Correct Example](http://www.sscce.org/). 2) One way to get image(s) for an example is to hot link to images seen in [this Q&A](http://stackoverflow.com/q/19209650/418556). 3) See [What is a stack trace, and how can I use it to debug my application errors?](http://stackoverflow.com/q/3988788/418556) & [What is a Null Pointer Exception, and how do I fix it?](http://stackoverflow.com/q/218384/418556) — Andrew Thompson, Jan 20 '16 at 15:09
BTW - `JLabel monsterAttack = new JLabel("src/images/monsterAttack.jpg");` You realized that this label will show (very odd looking) text, right? The `String` passed in the constructor for a `JLabel` will be interpreted as text rather than a path to a file to be used as an image icon. — Andrew Thompson, Jan 20 '16 at 15:10

score 1 · Answer 1 · answered Jan 20 '16 at 13:14

1

There are some problems with attempting to update a Swing data structure from another thread. You need to use invokeAndWait or invokeLater from your timer to make your changes in the Swing event handling thread.

answered Jan 20 '16 at 13:14

Romain-p

518
2
9
26

could you give me an example? – noobAlert Jan 21 '16 at 23:22
SwingUtilities.invokeLater(new Runnable() { public void run() { action(); } }); – Romain-p Jan 22 '16 at 18:55

How to change an Image in JFrame when a timer reaches a number?

1 Answers1