import java.awt.*;
import java.applet.*;

public class SchrodingerII extends Applet {

double x,xold,E,Eold,E0,dx,phi,phi_old,dphi,dphi_old,d2phi,V;
double p;
Panel p1;
Button b1;
Label l1,l2;
Scrollbar s1;
Choice Potential;
String initialE=" Energy= ";
String parity="Parity= ";
int type;

public void init(){
setLayout(new BorderLayout());
p1=new Panel();
b1=new Button("change parity");
l1=new Label(initialE + "0.1" );
l2=new Label(parity + "1.0");
s1=new Scrollbar(Scrollbar.HORIZONTAL,200,0,0,20001);
p1.setLayout(new GridLayout(2,3,6,6));
Potential=new Choice();
Potential.addItem("Square");
Potential.addItem("Triangular");
p1.add(l1);
p1.add(l2);
p1.add(Potential);
p1.add(s1);
p1.add(b1);
add("South",p1);
dx=0.001;p=1.0;
type=0;
}

public void paint(Graphics g){
g.setColor(Color.white);
g.fillRect(10,10,400,300); 
g.setColor(Color.red);
g.drawRect(10,10,400,300); 
g.drawLine(10,160,410,160); // draw the well
g.drawLine(210,10,210,310);
if(type==0){
g.drawLine(10,100,130,100);
g.drawLine(130,100,130,160);
g.drawLine(130,160,290,160);
g.drawLine(290,160,290,100);
g.drawLine(290,100,410,100);}
else{
g.drawLine(130,100,210,160);
g.drawLine(210,160,290,100);
g.drawLine(290,100,410,100);
g.drawLine(10,100,130,100);}

g.drawString("-4.0",123,171);
g.drawString("4.0", 283,171);
g.drawString("x",400,716);
g.drawString("E", 215,18);

if(p>=0.0){phi=1.0;x=0.0;dphi=0.0;}
else{phi=0.0;x=0.0;dphi=1.0;}

g.setColor(Color.blue);
do {
x=x+dx;
if(type==0){
if(Math.abs(x)>4.0){
V=8.0;}
else
V=0.0;}
else{
if(Math.abs(x)>4.0){
V=8.0;}
else
V=Math.abs(2.0*x);}

d2phi=2*(V-E)*phi;
dphi=dphi+d2phi*dx;
phi=phi+dphi*dx;
g.drawOval(210+(int)(20.0*x),160-(int)(50*phi),2,2);
g.drawOval(210-(int)(20.0*x),160-(int)(p*50*phi),2,2);
}while(Math.abs(phi)<=3 && x<10.0);
}

public boolean handleEvent(Event e){
if(e.target instanceof Scrollbar){
int value=((Scrollbar)e.target).getValue();
if(e.target==s1){
E=((double)value)/2000.0;
l1.setText(initialE + Double.toString(E));}
repaint();}
if(e.target == b1){
p=-p;l2.setText(parity + Double.toString(p));
repaint();}
else if(e.target instanceof Choice){
type=Potential.getSelectedIndex();repaint();}
return true;}


}