On a canvas can not appear

Question

I Tried to draw a simulation on my canvas canvas,but it could not appear only a blank screen. I only change "public class grafik extends java.applet.Applet" in to "class grafik extends java.awt.Canvas"
whats wrong with my code?

Answer 1

this is the code:
import java.awt.*;
class grafik extends java.awt.Canvas implements Runnable {
int wx,wy,yoff,xpts[],ypts[],nx;
double x0,xmin,xmax,dx,ymin,ymax,dy,xscale,yscale,tmin,t,dt;
double hbar,mass,epsilon,width,vx,vwidth,energy,energyScale;
complex Psi[],EtoV[],alpha,beta;
Thread kicker = null;
public void init() {
wx = size().width;
wy = size().height;
resize(wx,wy);
setBackground(Color.white);
nx = wx / 2;
yoff = 50;
wy -= yoff;
xpts = new int[nx];
ypts = new int[nx];
Psi = new complex[nx];
EtoV = new complex[nx];
energyScale = 1;
initPhysics();
public void initPhysics() {
x0 = -2;
xmin = -3;
xmax = 3;
dx = (xmax-xmin)/(nx-1);
xscale = (wx-0.5)/(xmax-xmin);
ymin = -1.5;
ymax = 1.5;
dy = (ymax-ymin)/(wy-1);
yscale = (wy-0.5)/(ymax-ymin);
tmin = 0;
t = tmin;
hbar = 1;
mass = 100;
width = 0.50;
vwidth = 0.25;
vx = 0.25;
dt = 0.8 * mass * dx * dx / hbar;
epsilon = hbar * dt /( mass * dx * dx );
alpha = new complex(0.5 * (1.0+Math.cos(epsilon/2))
, -0.5 * Math.sin(epsilon/2));
beta = new complex((Math.sin(epsilon/4))*Math.sin(epsilon/4)
, 0.5 * Math.sin(epsilon/2));
energy = 0.5 * mass * vx * vx ;
for(int x=0;x<nx;x++){
double r,xval;
xval = xmin + dx*x;
xpts[x] = (int)(xscale*(xval - xmin));
r = Math.exp(-((xval-x0)/width)*((xval-x0)/width));
Psi[x] = new complex(r*Math.cos(mass*vx*xval/hbar),
r*Math.sin(mass*vx*xval/hbar) );
r = v(xval)*dt/hbar;
EtoV[x] = new complex( Math.cos(r), -Math.sin(r) );
double v(double x) {
return
(Math.abs(x) < vwidth) ? ( energy* energyScale ) : 0 ;
public void paint(Graphics g) {
MakeGraph(g);
public void MakeGraph(Graphics g) {
int ix,iy;
int jx,jy;
//g.setColor(Color.black);
//g.drawRect(0,yoff,wx-1,wy-1);
g.setColor(Color.red);
ix = (int)(xscale*0.5*(xmax-xmin-2*vwidth));
jx = (int)(xscale*0.5*(xmax-xmin+2*vwidth));
iy = (int)(wy-1 - yscale*(0.5*ymax*energyScale - ymin));
jy = (int)(wy-1 - yscale*(0 - ymin));
g.drawLine(ix,yoff+iy,ix,yoff+jy);
g.drawLine(jx,yoff+iy,jx,yoff+jy);
g.drawLine(ix,yoff+iy,jx,yoff+iy);
g.setColor(Color.blue);
for(int x=0;x<nx;x++)
ypts[x] = yoff + (int)( wy-1 -
yscale* (Psi[x].re-ymin ) );
for (int x = 0 ; x < nx-1 ; x++ )
g.drawLine(xpts[x], ypts[x], xpts[x + 1], ypts[x+1]);
g.setColor(Color.black);
for(int x=0;x<nx;x++)
ypts[x] = yoff + (int)( wy-1 -
yscale* (Psi[x].re*Psi[x].re+Psi[x].im*Psi[x].im-ymin ) );
for (int x = 0 ; x < nx-1 ; x++ )
g.drawLine(xpts[x], ypts[x], xpts[x + 1], ypts[x+1]);
public void run() {
while ( kicker != null ){
step();step();step();
t += dt;
repaint();
try {
Thread.sleep(60);
} catch (InterruptedException e) {
break;
* Start the applet by forking an animation thread.
public void start() {
if (kicker == null) {
kicker = new Thread(this);
kicker.start();
* Stop the applet. The thread will exit because kicker is set to null.
public void stop() {
if (kicker != null) {
kicker.stop();
kicker = null;
public boolean mouseDown(java.awt.Event evt, int x, int y) {
requestFocus();
if( null != kicker ) stop();
else start();
return true;
public void step(){
complex x = new complex(0,0);
complex y = new complex(0,0);
complex w = new complex(0,0);
complex z = new complex(0,0);
for(int i=0;i<nx-1;i+=2){
x.set(Psi);
y.set(Psi[i+1]);
w.mult(alpha,x);
z.mult(beta,y);
Psi[i+0].add(w,z);
w.mult(alpha,y);
z.mult(beta,x);
Psi[i+1].add(w,z);
for(int i=1;i<nx-1;i+=2){
x.set(Psi[i]);
y.set(Psi[i+1]);
w.mult(alpha,x);
z.mult(beta,y);
Psi[i+0].add(w,z);
w.mult(alpha,y);
z.mult(beta,x);
Psi[i+1].add(w,z);
x.set(Psi[nx-1]);
y.set(Psi[0]);
w.mult(alpha,x);
z.mult(beta,y);
Psi[nx-1].add(w,z);
w.mult(alpha,y);
z.mult(beta,x);
Psi[0 ].add(w,z);
for(int i=0;i<nx;i++){
x.set(Psi[i]);
Psi[i].mult(x,EtoV[i]);
x.set(Psi[nx-1]);
y.set(Psi[0]);
w.mult(alpha,x);
z.mult(beta,y);
Psi[nx-1].add(w,z);
w.mult(alpha,y);
z.mult(beta,x);
Psi[0 ].add(w,z);
for(int i=1;i<nx-1;i+=2){
x.set(Psi[i]);
y.set(Psi[i+1]);
w.mult(alpha,x);
z.mult(beta,y);
Psi[i+0].add(w,z);
w.mult(alpha,y);
z.mult(beta,x);
Psi[i+1].add(w,z);
for(int i=0;i<nx-1;i+=2){
x.set(Psi[i]);
y.set(Psi[i+1]);
w.mult(alpha,x);
z.mult(beta,y);
Psi[i+0].add(w,z);
w.mult(alpha,y);
z.mult(beta,x);
Psi[i+1].add(w,z);
public double Norm() {
double sum = 0.0;
for(int x=0;x<nx;x++)
sum += Psi[x].re*Psi[x].re + Psi[x].im*Psi[x].im;
return sum;
class complex {
double re,im;
complex(double x,double y){
re = x;
im = y;
public void add(complex a,complex b){
re = a.re + b.re;
im = a.im + b.im;
public void mult(complex a,complex b){
re = a.re * b.re - a.im * b.im;
im = a.re * b.im + a.im * b.re;
public void set(complex a){
re = a.re;
im = a.im;