CheckBox.java

public class CheckBox {
  
  private final MutableCheckbox mutable = this::setState;
  private final ReadOnlyCheckbox readOnlyView = this::getState;
  
  /* ... */
  
  // Provide the view interface for the Controller.
  public MutableCheckbox getMutable () {
    return mutable;
  }
  
  // Provide the read-only view interface.
  public ReadOnlyCheckbox getReadOnlyView () {
    return readOnlyView;
  }
}