Java SE (Java Platform, Standard Edition)

I'm having difficulty correctly changing a custom component on a JFrame while the program that displays this is running.

My situation can be described as follow:

I have a global variable which of type CellularAutomaton<Cell>.
This class is a generic abstract class that extends JComponent with a implemented paintComponent( ) function that uses a abstract method drawShape() to draw a single cell in a cellular automaton.

Firstly I assign this gloabal variable to some subclass that implements the above mentioned class and then add it to a JFrame which is then displayed.

The problem is that when a certain button is triggered I want to display a new componet instead of the above mentioned component. This new component also extends the same abstract class as the old one.
I do this by assigning the golbal variable to the desired component, but then the JFrame that contains this, does not repaint it, no matter what.

All the above mentioned components' paintComponent( ) functions works correctly, but as soon as I make that assignment the JFrame no longer repaints that component.

public class Main {
  ...
  CellularAutomaton<Cell>ca; //the global variable mentioned above
  ...
  public Main() {
     ...
     JFrame frame = ...
     ca = someCA;
     frame.add(ca)  //works fine if ca remains the same
     frame.setVisible(true);
     ...
  }

  //the actionListener for when the above mentioned button
  class DisplayHandler implements ActionListener{		
    public void actionPerformed(ActionEvent e){
      ca=someOtherCA;
      ca.repaint(); //does nothing after assingment
    }             
  }

Any help would be much appreciated considering this project must be in by tommorow, sigh.