Swapping JSplitPane

Question

public static void setCurrentPane (JSplitPane newPane){
          contentHolder.remove(currentPane);  //contentHolder is a JPanel, currentPane is JSplitPane
          System.out.println ("currentPane removed");
          currentPane = newPane;
          contentHolder.add(currentPane);
          System.out.println ("currentPane added");
     }I have a main class which includes the above method. In the main class, there is also a JFrame which holds everything. Several other classes call the setCurrentPane() method to swap the JSplitPane that is in contentHolder. It works sometimes, and other times, it causes the program to lock up. There is nothing complex in the JSplitPanes, only JButtons and JLabels and I think that I have narrowed it down to this little piece of code. The whole code for the MainClass is directly below and code that example code that calls this class is below that.
Any help is greatly appreciated.
package globalVars;
import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JSplitPane;
import javax.swing.UIManager;
import subject.MathSubject;
import subject.Science;
import subject.StarterView;
public class MainClass {
     private static JSplitPane currentPane;
     private static JSplitPane previousPane;
     private static JSplitPane oldestPane;
     private static JFrame mainWindow;
     private static Container contents;
     private static JLabel title = new JLabel();
     private static JButton subjectNavButton;
     private static java.awt.Dimension navButtonSize = new java.awt.Dimension (125, 20);
     private static JButton catNavButton;
     private static JPanel contentHolder;
     private static JLabel navLabel = new JLabel (new ImageIcon ("files/navImage.png"));
     private static JPanel navButtonHolder;
     private static java.awt.Dimension leftButtonSize = new java.awt.Dimension (180, 40);
     private static java.awt.Dimension rightButtonSize = new java.awt.Dimension (120, 160);
     private static int dividerLocation = 200;
     private static int dividerSize = 1;
     private static JPanel northPanel;
     private static ButtonListener buttonListener = new ButtonListener();
     public static java.awt.Dimension getRightSize(){
          return rightButtonSize;
     public static int getDividerLocations (){
          return dividerLocation;
     public static java.awt.Dimension getLeftSize (){
          return leftButtonSize;
     public static int getDividerSize(){
          return dividerSize;
     public static void setSubjectButton (String s){
          subjectNavButton.setText(s);
     public static void setCatButton (String s){
          catNavButton.setText(s);
     public static void setCurrentPane (JSplitPane newPane){
          oldestPane = previousPane;
          contentHolder.remove(currentPane);
          System.out.println ("currentPane removed");
          previousPane = currentPane;
          currentPane = newPane;
          contentHolder.add(currentPane);
          System.out.println ("currentPane added");
     public static void setTitle (String s){
          title.setText(s);
          title.setFont(title.getFont().deriveFont(18.0f));
     public static void main (String [] args){
          try {
               UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
          catch (Exception e){
               JOptionPane.showMessageDialog(null, "Cannot load system look and feel, using Java default. This may require re-installing JAVA");
          mainWindow = new JFrame();
          contents = mainWindow.getContentPane();
          previousPane = null;
          oldestPane = null;
          currentPane = new StarterView();
          subjectNavButton = new JButton ("Subject Nav Button");
          subjectNavButton.setPreferredSize(MainClass.navButtonSize);
          subjectNavButton.addActionListener(buttonListener);
          catNavButton = new JButton ("Category Nav Button");
          catNavButton.addActionListener(buttonListener);
          catNavButton.setPreferredSize(MainClass.navButtonSize);
          mainWindow.setDefaultCloseOperation( javax.swing.WindowConstants.EXIT_ON_CLOSE );
          contentHolder = new JPanel (new BorderLayout());
          setTitle ("Subjects");
          northPanel = new JPanel (new FlowLayout (FlowLayout.LEFT));
          northPanel.add(subjectNavButton);
          northPanel.add(new JLabel (new ImageIcon ("files/navImage.png")));
          northPanel.add(catNavButton);
          northPanel.add(new JLabel (new ImageIcon ("files/navImage.png")));
          northPanel.add(title);
          contentHolder.add(northPanel, BorderLayout.NORTH);
          contentHolder.add(currentPane, BorderLayout.CENTER);
          contents.add(contentHolder);
          mainWindow.setSize(755, 555);
          mainWindow.setTitle("StepAhead Interactive tools");
          mainWindow.setLocationRelativeTo(null);
          mainWindow.setVisible(true);
     static class ButtonListener implements ActionListener {
          public void actionPerformed (ActionEvent e){
               if (e.getSource() == catNavButton){
                    System.out.println ("Category HOYO");
                    //replaces the current display with the Category Associated with that Button
               if (e.getSource() == subjectNavButton){
                    if (subjectNavButton.getText().equals("Math")){
                         System.out.println ("Loading up Math Subject");
                         setCurrentPane (new MathSubject());
                    if (catNavButton.getText().equals("Science")){
                         System.out.println ("Loading up Science Subject");
                         setCurrentPane (new JSplitPane());
                    //replaces the current display with the Subject Associated with that Button
                    System.out.println ("Subject HOYO");
}CODE THAT CALLS setCurrentPane method
package categories.math;
import java.awt.event.*;
import java.awt.*;
import globalVars.MainClass;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSplitPane;
import button.rightButton;
import chapters.NumbersChapters.*;
public class Numbers extends MathCategories implements ActionListener{
     private JPanel rightPane;
     private JButton division;
     private JButton numberPatterns;
     private JButton growthRates;
     private JButton fractions;
     private JButton remainders;
     private JButton counting;
     private JButton probability;
     public Numbers (){
          super();
          rightPane = new JPanel(new FlowLayout (FlowLayout.LEFT));
          numberPatterns = new rightButton ("Number", "Patterns"); //rightButton is a class I created which extends JButton
//and pre-formats it to conform to a set look
          numberPatterns.addActionListener(this);
          numberPatterns.setPreferredSize(MainClass.getRightSize());
          growthRates = new JButton ("Growth Rates of Sequences");
          growthRates.addActionListener(this);
          growthRates.setPreferredSize(MainClass.getRightSize());
          division = new JButton ("Division");
          division.addActionListener(this);
          division.setPreferredSize(MainClass.getRightSize());
          fractions = new JButton ("Fractions");
          fractions.addActionListener(this);
          fractions.setPreferredSize(MainClass.getRightSize());
          remainders = new JButton ("Remainders");
          remainders.addActionListener(this);
          remainders.setPreferredSize(MainClass.getRightSize());
          counting = new JButton ("Counting");
          counting.addActionListener(this);
          counting.setPreferredSize(MainClass.getRightSize());
          probability= new JButton ("Probability");
          probability.addActionListener(this);
          probability.setPreferredSize(MainClass.getRightSize());
          rightPane.add(numberPatterns);
          rightPane.add(growthRates);
          rightPane.add(division);
          rightPane.add(fractions);
          rightPane.add(remainders);
          rightPane.add(counting);
          rightPane.add(probability);     
          this.setRightComponent(rightPane);
     public void actionPerformed (ActionEvent e){
          super.actionPerformed(e);
          if (e.getSource() == numberPatterns){
               MainClass.setTitle ("Number Patterns");
               MainClass.setCurrentPane(new NumberPattern());
          if (e.getSource()== division){
               MainClass.setTitle ("Division");
               MainClass.setCurrentPane(new Division());
          if (e.getSource()== growthRates){
               MainClass.setTitle ("Growth Rates of Sequences");
               MainClass.setCurrentPane(new GrowthRate());
          if (e.getSource()== fractions){
               MainClass.setTitle ("Fractions");
               MainClass.setCurrentPane(new Division());
          if (e.getSource()== remainders){
               MainClass.setTitle ("Remainders");
               MainClass.setCurrentPane(new Division());
          if (e.getSource()== counting){
               MainClass.setTitle ("Counting");
               MainClass.setCurrentPane(new Division());
          if (e.getSource()== probability){
               MainClass.setTitle ("Probability");
               MainClass.setCurrentPane(new Division());
}

Answer 1

panel.remove(...);
panel.add(...);
panel.revalidate();
panel.repaint();If you need further help then you need to create a [Short, Self Contained, Compilable and Executable, Example Program (SSCCE)|http://homepage1.nifty.com/algafield/sscce.html], that demonstrates the incorrect behaviour.
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