BorderLayout problem with JSplitPane after adding JToolbar (Java)

Problem:

My program layout is fine, as below before I add JToolbar to BorderLayout.PAGE_START Here's a screenshot before JToolbar is added:

Here's how it looked like after adding JToolbar:

May I know what did I do wrong?

Here's the code I used:

    //Create the text pane and configure it.
    textPane = new JTextPane();
    -snipped code-
    JScrollPane scrollPane = new JScrollPane(textPane);
    scrollPane.setPreferredSize(new Dimension(300, 300));

    //Create the text area for the status log and configure it.
    changeLog = new JTextArea(5, 30);
    changeLog.setEditable(false);
    JScrollPane scrollPaneForLog = new JScrollPane(changeLog);

    //Create a split pane for the change log and the text area.
    JSplitPane splitPane = new JSplitPane(
            JSplitPane.VERTICAL_SPLIT,
            scrollPane, scrollPaneForLog);
    splitPane.setOneTouchExpandable(true);

    //Create the status area.
    JPanel statusPane = new JPanel(new GridLayout(1, 1));
    CaretListenerLabel caretListenerLabel =
            new CaretListenerLabel("Caret Status");
    statusPane.add(caretListenerLabel);

    //Create the toolbar
    JToolBar toolBar = new JToolBar();
    -snipped code-

    //Add the components.
    getContentPane().add(toolBar, BorderLayout.PAGE_START);
    getContentPane().add(splitPane, BorderLayout.CENTER);
    getContentPane().add(statusPane, BorderLayout.PAGE_END);

    //Set up the menu bar.
    actions = createActionTable(textPane);
    JMenu editMenu = createEditMenu();
    JMenu styleMenu = createStyleMenu();
    JMenuBar mb = new JMenuBar();
    mb.add(editMenu);
    mb.add(styleMenu);
    setJMenuBar(mb);

Please help, I'm new to GUI Building, and I don't feel like using Netbeans to drag and drop the UI for me... Thank you in advance.

Instead of using setSize() on the JFrame, set the preferred size of your center component as you do now and invoke pack(), which "Causes this Window to be sized to fit the preferred size and layouts of its subcomponents." Expanding on @Bragaadeesh's example,

public static void main(String[] args) {
    TestFrame frame = new TestFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.build();
    frame.pack();
    frame.setVisible(true);
}

Then, change to scrollPane.setPreferredSize(new Dimension(500, 300)) or JTextArea changeLog = new JTextArea(10, 30) to see the difference.