[Swing]Button-/Textfeldgröße/Layout(manager)

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JPanel;
import javax.swing.JSplitPane;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;

/**
 * @author jens
 * @version 0.0.1
 * 
 * Copyright 2007 Jens Melzer This program is distributed under the terms of the
 * GNU General Public License (license-copying.txt)
 * 
 */
public class Kanrinin extends javax.swing.JFrame {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private JMenuBar jMenuBarTop;
    private JMenu jMenuFile;
    private JMenuItem jMenuItemQuit;
    private JMenu jMenuHelp;
    private JMenuItem jMenuItemAbout;
    private JSplitPane jSplitPane;
    private JPanel jPanelLeftPanel;
    private JPanel jPanelleftTopPanel;
    private JButton jButtonHddLeft;
    /**
     * ActionListener for a normal program termination
     */
    private ActionListener exitNormalAction = new ActionListener() {
	public void actionPerformed(ActionEvent e) {
	    exit(0, null);
	}

    };

    /**
     * Auto-generated main method to display this JFrame
     */
    public static void main(String[] args) {
	SwingUtilities.invokeLater(new Runnable() {
	    public void run() {
		Kanrinin inst = new Kanrinin();
		inst.setLocationRelativeTo(null);
	    }
	});
    }

    public Kanrinin() {
	super();
	initGUI();
    }

    /**
     * @param code -
     *                exit code
     * @param errorMsg -
     *                error message, if the program termination is abnormal, can
     *                be null
     */
    private void exit(int code, String errorMsg) {
	if (code == 0 || errorMsg == null)
	    System.exit(code);
    }

    private void initGUI() {
	try {
	    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
	    this.setTitle("Kanrinin - the file manager");
	    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	    this.setSize(600, 700);
	    jMenuBarTop = new JMenuBar();
	    this.setJMenuBar(jMenuBarTop);
	    jMenuFile = new JMenu();
	    jMenuFile.setText("File");
	    jMenuItemQuit = new JMenuItem();
	    jMenuItemQuit.setText("Quit");
	    jMenuItemQuit.addActionListener(exitNormalAction);
	    jMenuFile.add(jMenuItemQuit);
	    jMenuBarTop.add(jMenuFile);
	    this.setVisible(true);
	    jSplitPane = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT);
	    this.setContentPane(jSplitPane);
	    jSplitPane.setOneTouchExpandable(true);
	    jSplitPane.setDividerLocation(0.5);
	    jPanelLeftPanel = new JPanel(new BorderLayout());
	    jPanelleftTopPanel = new JPanel();
	    jPanelLeftPanel.add(jPanelleftTopPanel, BorderLayout.NORTH);
	    jPanelleftTopPanel.setLayout(new BorderLayout());
	    jSplitPane.setLeftComponent(jPanelLeftPanel);
	
	    
	    jPanelleftTopPanel.add(new JComboBox(new Object[]{"test", "Test3"}),BorderLayout.NORTH);
	    

	    JPanel rightPanel = new JPanel();
	    rightPanel.setBackground(Color.YELLOW);
	    jSplitPane.setRightComponent(rightPanel);
	    jSplitPane.setResizeWeight(0.5);

	} catch (Exception e) {
	    e.printStackTrace();
	    exit(-1, "exception while initialising gui");
	}
    }
}