Getting JPanel size

Hello everybody,

I have a problem with getting the correct size of the JPanel using getWidth() and getHeight() methods. The program is supposed to plot the function in the rectangle and should also have some text fields and a button. The problem is that the window has to be resizable and for that i need to use abovementioned methods which in my case return 0. I did some internet digging and I found out that reason for that might be either not using the layout manager (which I`m not supposed to use) or the fact that the panel is not fitted to the frame yet. Here`s the code:

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.*;
import javax.swing.text.AbstractDocument.Content;

import java.awt.*;
import java.lang.Math;

import java.awt.event.*;
import java.awt.geom.Line2D;
import java.awt.geom.Rectangle2D;

public class Project7
{
	public static void main(String[] args)
	{		
		SmpWindow wnd = new SmpWindow();
		wnd.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		wnd.setVisible(true);
		wnd.setBounds(70, 70, 1000, 700);
		wnd.setTitle("Function plotting window by Qd");
	}
}

class SmpWindow extends JFrame
{
	public SmpWindow()
	{
		Container contents = getContentPane();
		contents.add(new DrawWndPane());
	}
}

class DrawWndPane extends JPanel implements ActionListener
{
	JButton	button = new JButton("Reset");
	JTextField field1 = new JTextField("0", 1);
	JTextField field2 = new JTextField("10", 1);
	Label l1 = new Label("X min");
	Label l2 = new Label("X max");
	int wd, hg;
	DrawWndPane()
	{
		super();
		setLayout(null);
		setBackground(Color.white);
		button.setBounds(10, hg - 80, 70, 30); //Here I have to use getHeight()
		add(button);
		field1.setBounds(100, hg - 80, 60, 20);
		add(field1);
		field2.setBounds(180, hg - 80, 60, 20);
		add(field2);
		button.addActionListener(this);
		field1.addActionListener(this);
		field2.addActionListener(this);
		l1.setSize(40, 25);
		l1.setLocation(110, 100); 
		add(l1);
		l2.setSize(40, 25);
		l2.setLocation(190, 100);
		add(l2);
	}
	
 	public void actionPerformed(ActionEvent event)
	{
		Object source = event.getSource();		
		if (source == button)
		{ 
			field1.setText("0");
			field2.setText("10");			
		}
        repaint();    
	}
 	
 	public void paintComponent(Graphics g) //In this method I`ll need height and width of the panel as well
	{
		g.setColor(Color.white);
		super.paintComponent(g);
		Graphics2D g2d = (Graphics2D) g;
		int xmax, xmin;
		try
		{
			xmin = Integer.parseInt(field1.getText());
		}
		catch (Exception e)
		{
			field1.setText("0");
			xmin = 0;
		};
		try
		{
			xmax = Integer.parseInt(field2.getText());
		}
		catch (Exception e)
		{
			field1.setText("10");
			xmax = 10;
		};
		g2d.setColor(Color.black);
		g2d.drawRect(70, 20, wd, hg); //Need getWidth() and getHeight() here
	}
 	
}
}

How can I get proper width and height values to use them in the DrawWndPane constructor and PaintComponent function?

If I replace wd and hg in that last line with "getWidth() / 2" and "getHeight() / 2" respectively, I get a rectangle that resizes as I resize the window. So what's not working for you?
I added the "/ 2" to make sure the rectangle doesn't fall off the screen.

Oh, so that`s actually working. I confused it with a problem from another project. Anyway, the problem with constructor still remains, I`d appreciate any help.

Lucas Quick wrote:Anyway, the problem with constructor still remains, I`d appreciate any help.

I'm sorry, I read the whole thread three times and I don't see anything about constructors and problems therewith.

The problem is that when I use getHeight() in the DrawWndPane constructor to determine the position of button and text fields the returned value is 0, so effectively it creates the button above the panel. I`d like the method to return the real height of the panel.

Can't be done. You can't know the size of a component until it's been materialized on the screen.

Well, I did a workaround that using the componentListener to watch for window resizing. Still, thanks for quick replies.

This is what layout managers are for - to reposition the child components as necessary. (Well ok, also to determine the preferred size of your container.) If you can't find any layout manager that does what you want you can write one yourself. A quick attempt, as an inner class of DrawWndPane:

private class DrawWndPaneLayoutManager
{
    public void addLayoutComponent(String name, Component comp) {}

public void removeLayoutComponent(Component comp) {}

public Dimension preferredLayoutSize(Container parent)
    {
        synchronized (target.getTreeLock())
        {
            // calculate the preferred size for the parent container, based on button, field1, field2, l1 and l2
        }        
    }

public Dimension minimumLayoutSize(Container parent)
    {
        // like the above but returning the minimum size instead of the preferred size
    }

public void layoutContainer(Container parent)
    {
        synchronized (target.getTreeLock())
        {
            int width = getWidth(); // calls method of enclosing DrawWndPane instance
            int height = getHeight(); // likewise

button.setBounds(10, height - 80, 70, 30);
            field1.setBounds(100, height - 80, 60, 20);   
            field2.setBounds(180, height - 80, 60, 20);   
            l1.setSize(40, 25);   
            l1.setLocation(110, 100);    
            l2.setSize(40, 25);   
            l2.setLocation(190, 100);   
        }
    }
}