每次最小化并重新打开Java窗口时，图形都会更改

Question

I got a bit of a problem which I am completely baffled about. Not even sure where to start to debug the problem.

I have a JFrame which promotes the user to enter a number, lets say the number was 4. I sent this number to my paint component to create a vertical line of 4 x 50. SO the line should be 200 in length. Which it does.

But if I minimise and reopen the window, that 4 seems to be multiplied again by 50 giving 200. Then that again is multiplied by 50 making the line 10,000.

I placed my paint component code in hope that it would help as the issue must be there, but if more code is needed I'll be happy to post.

class mainPanel extends JPanel
{
    int processes;
    public mainPanel(int x) //the value x is passed from another class, this was the number the user chooses...i.e 4
    {
    processes = x;
    setBorder(BorderFactory.createLineBorder(Color.LIGHT_GRAY, 5));
    }

    public Dimension getPreferredSize() {
        return new Dimension (1000, 1000);
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);   
    int storedProcesses = processes;

        // Draw Title
    g.setFont(new Font("TimesRoman", Font.PLAIN, 28)); 
        g.drawString("We place the title here",380,50);
    processes = processes * 50;
    g.drawLine(100,100,100, processes+100); //Vertical (down) line

    //labels for vertical line
    g.setFont(new Font("TimesRoman", Font.PLAIN, 20));
    int y = 125;
    for (int i=1; i<=storedProcesses; i++) //this loop keeps repeating and getting larger for some unknown reason...then its repainting my JFrame
    {
        g.drawString(String.valueOf(i), 70,y);
        y=y+50;
        System.out.println("Loop" + storedProcesses); //used for debugging
    }

    g.drawLine(100,processes+100,1000,processes+100); //Horizontal (across) line
    }  
}

I've attached some screen shots to illustrate what's going on with 1 process as an example.

Before I minimise the window (this is fine):

This is after I minimise and re maximise the window

Answer 1

You can't control when Swing invokes the paintComponent() method. Therefore you should NEVER change a property of your class in the paintComponent() method. All variables that you manipulate in the paintComponent() method should be local variables.

processes = processes * 50;

Your current code is modifying the "processes" variable. Don't do this.