import processing.opengl.*;

import processing.core.PApplet;

public class Main extends PApplet{

 public abstract class View extends PApplet{

   abstract public void openView();

   abstract public void closeView();
 }

 public class View1 extends View{

   public void openView(){
     println("opened view 1");
   }

   public void closeView(){
     println("closed view 1");
   }

   public void draw(){
     background(255,0,0);
   }

 }

 public class View2 extends View{

   public void openView(){
     println("opened view 2");
   }

   public void closeView(){
     println("closed view 2");
   }

   public void draw(){
     background(0,255,0);
   }

 }

 View view1;
 View view2;

 View currentView;

 private void initView(final View i_view){
   i_view.g = g;
   i_view.width = width;
   i_view.height = height;
   i_view.setup();
 }

 public void setup(){
   size(800, 600, OPENGL);

   view1 = new View1();
   initView(view1);

   view2 = new View2();
   initView(view2);

   currentView = view1;
 }

 public void draw(){
   try{
     currentView.draw();
   }
   catch(Exception e){
     e.printStackTrace();
   }
 }

 private void openView(final View i_view){
   currentView.closeView();
   currentView = i_view;
   currentView.openView();
 }

 public void keyPressed(){
   if(currentView == view1){
     openView(view2);
   }
   else{
     openView(view1);
   }
 }
}