I hope this isn't a stupid first question; I can't seem to find an answer anyway.
I have this JFrame
constructor where a JPanel
is added to the JFrame
. The JPanel
paints a Rectangle
in the JFrame
, and that's fine. However , if I add an ImageIcon
object as in the code below (for later use), the rectangle isn't painted. It does appear if I resize the window though.
One solution is to put the setVisible(true)
as the last line, or to instantiate the ImageIcon
above the constructor, but I really want to understand this. It doesn't make sense to me that an object not even used can cause this behaviour. Thanks.
public class AJFrame extends JFrame {
ImageIcon ii;
public AJFrame() {
setSize(400,400);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setLocationRelativeTo(null);
setVisible(true);
ImageIcon ii = new ImageIcon("Untitled.png");
JPanel jp = new JPanel() {
@Override
protected void paintComponent(Graphics g) {
g.fillRect(0, 0, 50, 50);
}
};
add(jp);
}
public static void main(String[] args) {
AJFrame jf = new AJFrame();
}
}
All actions within a frame should be done in the EDT (Event Dispatching Thread) of Swing. Therefore the right way to start your frame is
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new AJFrame().setVisible(true);
}
});
So maybe it all comes down to the wrong start of your frame.
The main routine of a Java program is not started within the EDT. All Swing actions that are not within the EDT could produce strange refresh/visibility issues.
Here is the complete sourcecode:
public class AJFrame extends JFrame {
ImageIcon ii;
public AJFrame() {
setSize(400, 400);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setLocationRelativeTo(null);
//setVisible(true);
//ImageIcon ii = new ImageIcon("Untitled.png");
JPanel jp = new JPanel() {
@Override
protected void paintComponent(Graphics g) {
g.fillRect(0, 0, 50, 50);
}
};
add(jp);
}
public static void main(String[] args) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new AJFrame().setVisible(true);
}
});
}
}
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