I'm trying to get the top right square to be the same width as the two below it and I'd like to get the JTextArea below to match width as well. Any ideas?

It seems like no matter what I set the sizes to it's doing whatever it wants. For instance the Output JTextArea is set to just one column. The top image is (700x250) and the two half-images are (350x250).

Java Code:
public class MyApplet extends Applet{
    private static final long serialVersionUID = 1L;
    private JTextArea input_data;
    private JTextArea input_jmax;
    private JTextArea input_gibbs;
    private JTextArea input_burnin;
    private JTextArea output_text;
    private JLabel output_graph;
    private JLabel output_burn1;
    private JLabel output_burn2;
    private static Graphics g=null;

    public void init () {
        //INPUT
        this.input_data = new JTextArea("Enter Data", 30, 30);
        JScrollPane data_pane= new JScrollPane(input_data);
        this.input_jmax = new JTextArea("Polya-Tree Levels", 1, 30);
        this.input_gibbs = new JTextArea("Gibbs Iterates", 1, 30);
        this.input_burnin = new JTextArea("Burnin", 1, 30);
        //OUTPUT
        Dimension D;
        D = new Dimension(700, 250);
        Image start;

        this.output_text = new JTextArea("####################Output####################",15,1);
        this.output_text.setEditable(false);
        JScrollPane output_pane= new JScrollPane(output_text);

        this.output_burn1 = new JLabel();
        D = new Dimension(345,250);
        start = createImage((int) D.getWidth(), (int) D.getHeight());
        g = start.getGraphics();
        g.setColor(Color.WHITE);
        g.fillRect(0,0,345,250);
        output_burn1.setIcon(new ImageIcon(start));

        this.output_burn2 = new JLabel();
        D = new Dimension(345, 250);
        start = createImage((int) D.getWidth(), (int) D.getHeight());
        g = start.getGraphics();
        g.setColor(Color.WHITE);
        g.fillRect(0,0,345,250);
        output_burn2.setIcon(new ImageIcon(start));

        this.output_graph = new JLabel();
        start = createImage((int) D.getWidth(), (int) D.getHeight());
        g = start.getGraphics();
        g.setColor(Color.WHITE);
        g.fillRect(0,0,700,250);
        output_graph.setIcon(new ImageIcon(start));

        //BUTTON
        JButton b = new JButton("Process Data");

        //set size
public class MyApplet extends Applet{
	private static final long serialVersionUID = 1L;
	private JTextArea input_data;
	private JTextArea input_jmax;
	private JTextArea input_gibbs;
	private JTextArea input_burnin;
	private JTextArea output_text;
	private JLabel output_graph;
	private JLabel output_burn1;
	private JLabel output_burn2;
	private static Graphics g=null;

	public void init () {
		//INPUT
		this.input_data = new JTextArea("", 30, 30);
		JScrollPane data_pane= new JScrollPane(input_data);
		this.input_jmax = new JTextArea("", 1, 30);
		this.input_gibbs = new JTextArea("", 1, 30);
		this.input_burnin = new JTextArea("", 1, 30);
		//this.input_jmax = new JTextArea("Polya-Tree Levels", 1, 30);
		//this.input_gibbs = new JTextArea("Gibbs Iterates", 1, 30);
		//this.input_burnin = new JTextArea("Burnin", 1, 30);
		
		//OUTPUT
		Dimension D;
		Image start;

		this.output_text = new JTextArea("",15,1);
		this.output_text.setEditable(false);
		JScrollPane output_pane= new JScrollPane(output_text);

		this.output_burn1 = new JLabel();
		D = new Dimension(345,250);
		start = createImage((int) D.getWidth(), (int) D.getHeight());
		g = start.getGraphics();
		g.setColor(Color.WHITE);
		g.fillRect(0,0,345,250);
		output_burn1.setIcon(new ImageIcon(start));

		this.output_burn2 = new JLabel();
		D = new Dimension(345, 250);
		start = createImage((int) D.getWidth(), (int) D.getHeight());
		g = start.getGraphics();
		g.setColor(Color.WHITE);
		g.fillRect(0,0,345,250);
		output_burn2.setIcon(new ImageIcon(start));

		this.output_graph = new JLabel();
		start = createImage((int) D.getWidth(), (int) D.getHeight());
		g = start.getGraphics();
		g.setColor(Color.WHITE);
		g.fillRect(0,0,700,250);
		output_graph.setIcon(new ImageIcon(start));

		//BUTTON
		JButton b = new JButton("Process Data");

		//set size
		setSize(1200, 600);
		setBackground(Color.lightGray);

		//Create Input Side
		JPanel inputPanel = new JPanel();
		inputPanel.setLayout(new BoxLayout(inputPanel, BoxLayout.Y_AXIS));
		inputPanel.setBackground(Color.LIGHT_GRAY);
		inputPanel.add(data_pane);
		inputPanel.add(Box.createVerticalStrut(10));
		inputPanel.add(input_jmax);
		inputPanel.add(Box.createVerticalStrut(10));
		inputPanel.add(input_gibbs);
		inputPanel.add(Box.createVerticalStrut(10));
		inputPanel.add(input_burnin);
		inputPanel.add(Box.createVerticalStrut(10));
		inputPanel.add(b);

		//Create Output Side
		JPanel burninPanel = new JPanel();
		burninPanel.setBackground(Color.LIGHT_GRAY);
		burninPanel.setLayout(new BoxLayout(burninPanel, BoxLayout.X_AXIS));
		burninPanel.add(output_burn1);
		burninPanel.add(Box.createHorizontalStrut(10));
		burninPanel.add(output_burn2);
		
		JPanel outputPanel = new JPanel();
		outputPanel.setBackground(Color.lightGray);
		outputPanel.setLayout(new BoxLayout(outputPanel, BoxLayout.Y_AXIS));
		outputPanel.add(output_graph);
		outputPanel.add(Box.createVerticalStrut(10));
		outputPanel.add(burninPanel);
		outputPanel.add(Box.createVerticalStrut(10));
		outputPanel.add(output_pane);


		this.setVisible(true); 
		GroupLayout layout = new GroupLayout(this);
		layout.setAutoCreateGaps(true);
		layout.setAutoCreateContainerGaps(true);
		layout.setHorizontalGroup(layout.createSequentialGroup()
				.addGroup(layout.createSequentialGroup()
						.addComponent(inputPanel)
						.addComponent(outputPanel)
						) 
				);
		layout.setVerticalGroup(layout.createSequentialGroup()
				.addGroup(layout.createParallelGroup(LEADING)
						.addComponent(inputPanel)
						.addComponent(outputPanel)
						)
				);
		this.setLayout(layout);        
		this.setVisible(true);

		Multiplicity ca = new Multiplicity(input_data, input_jmax, input_gibbs, input_burnin, output_text,output_graph);
		b.addActionListener(ca);
	}
}