problem with BorderLayout

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JSplitPane;
import javax.swing.JTabbedPane;
import javax.swing.JTable;
import javax.swing.JTextArea;
import javax.swing.JTree;
import javax.swing.border.BevelBorder;
import javax.swing.border.EmptyBorder;

public class Main extends JFrame {

	private static final long serialVersionUID = -573737534454859870L;
	private JPanel contentPane;
	private JPanel northPanel;
	private JButton btnNew;
	private JButton btnOpen;
	private JButton btnSave;
	private JPanel southPanel;
	private JLabel statusLabel;
	private JTree tree = null;
	private JTabbedPane tabbedPane = null;
	private JSplitPane splitPane;
	private JScrollPane scrollPane;
	private JScrollPane scrollPane_1;
	private JTextArea textArea;
	private JTable table = null;
	private JScrollPane scrollPane_2;
	private JSplitPane centerSplit;

	/**
	 * Launch the application.
	 */
	public static void main(String[] args) {
		EventQueue.invokeLater(new Runnable() {
			public void run() {
				try {
					Main frame = new Main();
					frame.setVisible(true);
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}

	/**
	 * Create the frame.
	 */
	public Main() {
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setBounds(100, 100, 750, 500);
		contentPane = new JPanel();
		contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
		contentPane.setLayout(new BorderLayout(1, 1));
		setContentPane(contentPane);
		
		northPanel = new JPanel();
		northPanel.setBorder(new BevelBorder(BevelBorder.LOWERED, null, null, null, null));
		contentPane.add(northPanel, BorderLayout.NORTH);
		
		btnNew = new JButton("New");
		northPanel.add(btnNew);
		
		btnOpen = new JButton("Open");
		northPanel.add(btnOpen);
		
		btnSave = new JButton("Save");
		northPanel.add(btnSave);

		
		southPanel = new JPanel();
		southPanel.setBorder(new BevelBorder(BevelBorder.LOWERED, null, null, null, null));
		contentPane.add(southPanel, BorderLayout.SOUTH);
		
		tabbedPane = new JTabbedPane();
		
		centerSplit = new JSplitPane();
		JPanel panel = new JPanel();
		panel.add(centerSplit);
		contentPane.add(panel, BorderLayout.CENTER);
		
		splitPane = new JSplitPane();
		splitPane.setOrientation(JSplitPane.VERTICAL_SPLIT);
		tabbedPane.addTab("New tab", null, splitPane, null);
		
		scrollPane = new JScrollPane();
		splitPane.setLeftComponent(scrollPane);
		
		textArea = new JTextArea();
		textArea.setPreferredSize(new Dimension(600,200));
		scrollPane.setViewportView(textArea);
		
		scrollPane_1 = new JScrollPane();
		splitPane.setRightComponent(scrollPane_1);
		
		table = new JTable();
		scrollPane_1.setViewportView(table);
		
		statusLabel = new JLabel("");
		southPanel.add(statusLabel);
		
		scrollPane_2 = new JScrollPane();
		centerSplit.setLeftComponent(scrollPane_2);
		centerSplit.setRightComponent(tabbedPane);
		
		tree = new JTree();
		tree.setPreferredSize(new Dimension(100,200));
		scrollPane_2.setViewportView(tree);
	}

}

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