Java Swing NullPointerException when drawing
- by juFo
I'm using a custom JLayeredPane.
I have several Shapes which needed to be drawn on different layers in the JLayeredPane.
To test this I create a JPanel and ask its graphics. Then I draw a test rectangle on that JPanel (preparing the graphics) and in my paintComponent method from the JLayeredPane I finally draw everything. But this fails (NullPointerException).
public class MyCustomPanel extends JLayeredPane {
// test
JPanel testpane;
Graphics g2;
// test
// constructor
public MyCustomPanel() {
testpane = new JPanel();
this.add(testpane, new Integer(14));
g2 = testpane.getGraphics();
}
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g2.drawRect(10, 10, 300, 300);
}
}
// run:
//Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
// at view.MyCustomPanel.paintComponent(MyCustomPanel.java:65)
Why can't I draw on such a JPanel from within my JLayeredPane? I can draw directly on my JLayeredPane from within my paintComponent method but that's on the default Panel from the JLayeredPane. I need to create and draw on several layers which are added in my JLayeredPane.
What am I doing wrong? :s
