CODEWITHSUNDEEP
javaswingpaintcomponentjcomponent
Ryan Saxe
Ryan Saxe

Reputation: 17829

Java paintComponent running but not showing

so I just want to paint a square in a random part of the screen as a custon JComponent:

public void paintComponent(Graphics g){
    Graphics2D g2d = (Graphics2D) g;
    if( this.good ){
        g2d.setColor(Color.green);
    }
    else{
        g2d.setColor(Color.red);
    }
    g2d.fillRect(this.x, this.y, this.w, this.h);
    System.out.println("painting");
}

here is the method that calls painting via repaint()

private void stateChange(){
        
    double rand = Math.random();
        
    if (rand < 0.5){
        this.good = !this.good;
    }
    setLocation(this.x,this.y);
    repaint();
}

this.x and this.y are constantly changing, but I know that works. When I run my code, it prints "painting" where it should, but nothing is showing up. Am I doing something wrong?

extra code:

here is what I put for trying to get it to show up:

\\in JComponent constructore
setOpaque(true);
setVisible(true);
setSize(this.w,this.h);

Upvotes: 0

Views: 146

Answers (2)

MadProgrammer
MadProgrammer

Reputation: 347204

The problem, based on the example code you've provided, is the fact that you are actually painting out side of the bounds of viewable space of the component.

When painting, the top, left corner of the Graphics context is 0x0, Swing has already translated the Graphics context based on the position of the component, so...

g2d.fillRect(this.x, this.y, this.w, this.h);

Is actually (possibly) painting beyond the viewable area of the component. For example, if the x position is 10 and y is 10, but height and width is only 10, 10, you are painting at position 10x10, which would be beyond the viewable space of the component, instead, you should try something like...

g2d.fillRect(0, 0, this.w, this.h);

Or, based on your example code,

public void paintComponent(Graphics g){
    Graphics2D g2d = (Graphics2D) g;
    if( this.good ){
        g2d.setColor(Color.green);
    }
    else{
        g2d.setColor(Color.red);
    }
    super.paintComponent(g2d);
}

Instead....

Upvotes: 2

Hovercraft Full Of Eels
Hovercraft Full Of Eels

Reputation: 285403

My guess: you have a while (true) loop that ties up the Swing event thread, so while you are changing state, the GUI can't repaint itself to show it happening. Either that or your JComponent's size is very small, too small to show the image.

For an answer that's more than a guess, you'll need to ask a more complete question with pertinent code.

Note that your paintComponent(...) method override is missing its call to the super's method.

Note: you can test the JComponent's size by adding a getSize() method in your paintComponent:

public void paintComponent(Graphics g){
    super.paintComponent(g);  // **** don't forget this.
    Graphics2D g2d = (Graphics2D) g;
    if( this.good ){
        g2d.setColor(Color.green);
    }
    else{
        g2d.setColor(Color.red);
    }
    g2d.fillRect(this.x, this.y, this.w, this.h);

    // TODO: ***** delete this lines
    System.out.println("painting");
    System.out.println(getSize());  // **** add this***
}

Note: you should not call setSize(...) on your component. It is usually misleading as it's often ignored by the layout managers.

Upvotes: 3

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