hs teacher needs help - display swing components with coordinates

[Jeff Borland]

hs teacher needs help -
hi folks,
im a high school teacher teaching a java class for the first time. The students are doing their final projects and I'm coming across some problems.
One student wants to use swing components to display numerous buttons and menus. He wants to know the best way to do this. I decided i need to use jbuttons (right?), and i thought to setlayout to null. As below:
Container c = getContentPane();
c.setLayout(null);
But i cant get menus or scrollpane (scrolling textarea) to work, any simple code to do that...
i and my students appreciate any help you can give
jeff

[Matthew Middleton]

If you set the content pane to null then you have to use the reshape(xCoor, yCoor, ht, width) class. if you have a JButton next, and a Container box, the code would look something like:
box.add(next);
next.reshape(5,5,100, 25);
this should be what you need, tell me if this helped
GOD Bless

[Jeff Borland]

i could get the button to work using .setBounds,
but is that the best way to specify coordinates...
and if so, do you have any code for menus that works with coordinates?
thanks,
jeff

[Nathan Pruett]

Setting the layout to null causes a lot of problems like this... what was the reason that led you to need to lay out components with specific coordinates? This usually leads to more problems than it solves. There's usually a way to nest layouts, use GridBagLayout, or even create your own layout that will let you achieve what you are trying to do without resorting to null layout.

[Craig Wood]

Simple code for working with null layout? No, not really. Using layout managers makes for simple code.

In the beginning a null layout appears to be an easy choice but as the example below shows it can be quite a chore to get any useful results with it. The one place it seems to work okay is when using mouse code to drag/move components around with.

Once you make friends with and learn to use a few layout managers, say, BorderLayout, FlowLayout, GridLayout and CardLayout, nesting panels opens a whole world of possibilities in putting things together. Later you can get to know more specialized layout managers like BoxLayout and GridBagLayout.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
public class LayoutTest
{
    static JScrollPane scrollPane;
    static JButton[] buttons;
    static JTextField[] textFields;
 
    public static void main(String[] args)
    {
        scrollPane = new JScrollPane();
        buttons = new JButton[4];
        textFields = new JTextField[4];
        for(int i = 0; i < buttons.length; i++)
        {
            buttons[i] = new JButton("Button " + (i + 1));
            textFields[i] =  new JTextField(8);
        }
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(getUIPanel(), "North");
        f.getContentPane().add(scrollPane);
        f.setSize(400,400);
        f.setLocation(200,200);
        f.setVisible(true);
    }
 
    private static JPanel getUIPanel()
    {
        final JButton
            flow = new JButton("flow"),
            grid = new JButton("grid"),
            gridbag = new JButton("gridbag"),
            not = new JButton("null");
        ActionListener l = new ActionListener()
        {
            public void actionPerformed(ActionEvent e)
            {
                JButton button = (JButton)e.getSource();
                Component c = null;
                if(button == flow)
                    c = getFlowPanel();
                if(button == grid)
                    c = getGridPanel();
                if(button == gridbag)
                    c = getGridBagPanel();
                if(button == not)
                    c = getNullPanel();
                scrollPane.getViewport().setView(c);
            }
        };
        flow.addActionListener(l);
        grid.addActionListener(l);
        gridbag.addActionListener(l);
        not.addActionListener(l);
        JPanel panel = new JPanel();
        panel.setBorder(BorderFactory.createTitledBorder("layout managers"));
        panel.add(flow);
        panel.add(grid);
        panel.add(gridbag);
        panel.add(not);
        return panel;
    }
 
    private static JPanel getFlowPanel()
    {
        JPanel panel = new JPanel();
        // so manager will wrap components within visible viewport bounds
        // otherwise we get all components in a single row
        panel.setPreferredSize(scrollPane.getPreferredSize());
        for(int i = 0; i < buttons.length; i++)
        {
            panel.add(buttons[i]);
            panel.add(textFields[i]);
       }
       return panel;
    }
 
    private static JPanel getGridPanel()
    {
        JPanel panel = new JPanel(new GridLayout(0,4));
        for(int i = 0; i < buttons.length; i++)
        {
            panel.add(buttons[i]);
            panel.add(textFields[i]);
        }
        return panel;
    }
 
    private static JPanel getGridBagPanel()
    {
        JPanel panel = new JPanel(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.weighty = 1.0;
        gbc.weightx = 1.0;
        gbc.insets = new Insets(5,5,5,5);
        for(int i = 0; i < buttons.length; i++)
        {
            panel.add(buttons[i], gbc);
            if((i + 1) % 2 == 0)
                gbc.gridwidth = gbc.REMAINDER;
            panel.add(textFields[i], gbc);
            gbc.gridwidth = 1;
        }
        return panel;
    }
 
    private static JPanel getNullPanel()
    {
        JPanel panel = new JPanel(null);
        Dimension size = scrollPane.getViewport().getSize();
        Component[] components = new Component[buttons.length + textFields.length];
        for(int i = 0; i < components.length; i += 2)
        {
            components[i] = buttons[i/2];
            components[i + 1] = textFields[i/2];
        }
        int width = size.width;
        int cols = components.length;
        int xInc = 0;
        for(int i = 0; i < components.length; i++)
        {
            int w = components[i].getPreferredSize().width;
            if(width - w > 0)
                width -= w;
            else
            {
                cols = i;
                xInc = width / (cols + 1);
                break;
            }            
        }
        if(cols == components.length)
            xInc = width / (cols + 1);
        int rows = (int)Math.ceil(components.length / (float)cols);
        int maxHeight = Math.max(buttons[0].getPreferredSize().height,
                            textFields[0].getPreferredSize().height);
        int yInc = (size.height - rows * maxHeight) / (rows + 1);
        int y = yInc;
        for(int i = 0; i < rows; i++)
        {
            int x = xInc;
            for(int j = 0; j < cols; j++)
            {
                int index = i * cols + j;
                if(index >= components.length)
                    continue;
                int w = components[index].getPreferredSize().width;
                int h = components[index].getPreferredSize().height;
                components[index].setBounds(x, y, w, h);
                panel.add(components[index]);
                x += w + xInc;
            }
            y += yInc + maxHeight;
        }
        return panel;
    }
}