import java.awt.*;
import java.applet.*;
import java.awt.event.*;
public class Exm5 extends Applet implements ActionListener
{
Button button1 = new Button();
Button button2 = new Button();
Label label1 = new Label();
int vxmin,vymin,vxmax,vymax; //screen coordinates
double xmin,ymin,xmax,ymax; //imaginary coordinates
double dx; //interval of x
double a; // parameter
double da; //interval of a
/* initializing */
public void init(){
String str;
xmin=-5;xmax=5;ymin=-3;ymax=7;
vxmin=0;vxmax=300;vymin=0;vymax=300;
dx=0.1;
a=1;da=0.1;
setLayout(null); //free layout
setSize(400,300); //size of this applet
add(button1);
button1.setLabel("+");
button1.setFont(new Font("Dialog", Font.PLAIN, 16));
button1.setBounds(320,40,20,20);
button1.addActionListener(this);
add(button2);
button2.setLabel("-");
button2.setFont(new Font("Dialog", Font.PLAIN, 16));
button2.setBounds(350,40,20,20);
button2.addActionListener(this);
add(label1);
str="a = "+Double.toString(a);
label1.setText(str);
label1.setFont(new Font("Dialog", Font.PLAIN, 16));
label1.setBounds(320,60,60,40);
}
public void paint(Graphics g)
{
double x1,y1,x2,y2;
//axes and scale
scale(g);
//graph
g.setColor(Color.blue);
x2=xmin;y2=func(x2);
for(x1=xmin;x1<=xmax;x1=x1+dx){
y1=func(x1);
Line(g,x1,y1,x2,y2);
x2=x1;y2=y1;
}
}
/* Convert imaginary coordinates to screen cordinates. */
public int mapX(double x){
int sx;
sx=vxmin+(int)((x-xmin)/(xmax-xmin)*(double)(vxmax-vxmin)) ;
return sx;
}
public int mapY(double y){
int sy;
sy=vymin+(int)((ymax-y)/(ymax-ymin)*(double)(vymax-vymin));
return sy;
}
/* Drawing Line */
public void Line(Graphics g,double x1,double y1,double x2,double y2){
g.drawLine(mapX(x1),mapY(y1),mapX(x2),mapY(y2));
}
/* Defining function */
public double func(double x){
double y;
y=a*x*x;
return y;
}
/* axes and lattice */
public void scale(Graphics g){
double x,y;
//back color
g.setColor(new Color(255, 255, 192));
g.fillRect(vxmin,vymin,vxmax-vxmin,vymax-vymin);
// scale
g.setColor(Color.lightGray);
for (x=xmin;x<=xmax;x=x+1){
Line(g,x,ymin,x,ymax);
}
for (y=ymin;y<=ymax;y=y+1){
Line(g,xmin,y,xmax,y);
}
// xy-axes
g.setColor(Color.black);
Line(g,0,ymin,0,ymax);
Line(g,xmin,0,xmax,0);
}
public void actionPerformed(ActionEvent event)
{
String str;
Object object = event.getSource();
if (object == button1){
a=a+da;
a=(double)(Math.round(10*a))/10;
repaint();
str="a = "+Double.toString(a);
label1.setText(str);
}
if (object == button2){
a=a-da;
a=(double)(Math.round(10*a))/10;
repaint();
str="a = "+Double.toString(a);
label1.setText(str);
}
}
}
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