每次我想要它时都不会调用paintComponent

Question

I was trying to visualize sorting algorithms with Graphics2D and Swing (dont know if thats a good idea, im just doing it for fun) in a little project and came to a point where I would call the update method and thus the paintCompenent method everytime an element in the array changes its value.

The problem is that the paintComponent method aparrently only gets called after the algorithm is finished. Here is the code of the algorithm:

private void sortBubble() {
    int n = array.length;
    do {            
        int newn = 1;
        for (int i = 0; i < n - 1; i++) {
            if (array[i] > array[i + 1]) {                  
                int index = array[i];                       
                array[i] = array[i + 1];                                    
                array[i + 1] = index;
                System.out.println("SWITCHED"); 
                this.setChanged();
                this.notifyObservers();
                newn = i + 1;                   
            }
        }
        n = newn;
    } while (n > 1);    
}

The code of the update method:

public void update(Observable o, Object arg) {
    if(draw!=null)  {
        drawPanel.remove(draw);         
    }       
    draw = new Plotter(array.array,this.getWidth(),this.getHeight());   
    drawPanel.add(draw);  
    drawPanel.validate();       
    System.out.println("UPDATED");
}

And the code of the JPanel class:

private void draw(Graphics g) {     
    g2d = (Graphics2D) g;
    int i;                  
    for(i=0;i<array.length;i++) {
        g2d.draw(new Line2D.Double(i, height, i, height-array[i]));             
    }           
}

@Override
public void paintComponent(Graphics g) {            
    super.paintComponent(g);
    draw(g);
    System.out.println("PLOTTED");
}   

Is there a way so the JPanel actually updates everytime a value changes?

Answer 1

Swing is a single threaded framework, that means that any long running/blocking code will cause the program to "stall", preventing it from been able to update the UI or respond to the user input.

See Concurrency in Swing for more details.

There are several ways you might fix this, you could use a SwingWorker or Swing Timer , depending on your needs/abilities.

See Worker Threads and SwingWorker and How to use Swing Timers for more details

Also have a look at java multiple graphics for an example of a visualised sorting implementation