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Thread: GUI Help

  1. #1
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    Default GUI Help

    Hey,

    I am making a test for my first GUI program.

    Here is the code so far:

    package Tests;
     
    import java.awt.*;
    import javax.swing.*;
    import java.awt.event.*;
     
    public class GUITest  {
     
    	private static class Display extends JPanel  {
     
    		public void paintComponent(Graphics g)  {
     
    			super.paintComponent(g);
    			g.drawString("This is my first GUI Test.", 20, 30);
    			g.drawString("Hello World!", 20, 40);
     
    		}
     
    	}
     
    	private static class ButtonHandler implements ActionListener  {
     
    		public void actionPerformed(ActionEvent e) {
    			System.exit(0);
    		}
     
    	}
     
    	public static void main(String[] arg)  {
     
    		JButton button = new JButton("Click to close");
    		Display displayPanel = new Display();
    		ButtonHandler listener = new ButtonHandler();
    		button.addActionListener(listener);
     
    		JFrame window = new JFrame("GUI Test");
    		window.setContentPane(content);
                                window.setSize(300, 300);
    		window.setLocation(100, 100);
    		window.setVisible(true);
     
    		JPanel content = new JPanel();
    	    content.add(displayPanel, BorderLayout.CENTER);
    		content.add(button, BorderLayout.SOUTH);
    		content.setLayout(new BorderLayout());
     
     
     
     
     
    	}
     
    }

    In the main() routine, the content in window.setContentPane(content); is underlined and it says it can't find the variable content, but it is clearly there under the JPanel definition (JPanel content = new JPanel().

    Help?

    -Silent


  2. #2
    Super Moderator pbrockway2's Avatar
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    Default Re: GUI Help

    In the main() routine, the content in window.setContentPane(content); is underlined and it says it can't find the variable content, but it is clearly there under the JPanel definition (JPanel content = new JPanel()
    content has to be declared before you use it. The compiler won't "read ahead" for a declaration, and things would get very confusing if it tried.

    -----

    Why do you have static classes defined? If you have trouble answering that in terms of what a static class is, then my advice would be to remove those classes. Oracle's Tutorial includes a graphical "Hello world" program that you could use as a model. As that code notes the use of invokeLater() means that the GUI construction occurs on the event dispatch thread (not in the thread that main() runs in) which can help avoid problems later.

    That code occurs in the context of the Getting Started with Swing section.

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    Default Re: GUI Help

    Thank you, I figured that out.

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    Think of me.... Mr.777's Avatar
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    Default Re: GUI Help

    Well, a simple example
    System.out.println(x);
    int x = 5;
    Oh God, why it can't find x???? I can see x in the program.
    Compiler starts compiling from the first line to last.
    Anyone who stops learning is old, whether at twenty or eighty. Anyone who keeps learning stays young. The greatest thing in life is to keep your mind young.

    - Henry Ford