It is a poorly-kept secret how programmers quail at embarking on learning a new concept. When they begin, they look like they were waiting for the dentist's drill and by the time they wind up, they give the impression they just got trampled in a thousand-cow stampede! The concept of threads, though relatively fresh, is by no means one of these gut-wrenching features of Java. We will address threads very soon, but let us first consider the following code..
From the subdirectory demo/TumblingDuke, we picked up the seventeen *.gif files and this is the way you can animate them.The above code is to display an image out of the 17 every time you click. As seen in the last chapter , an image was displayed wherever you clicked. Here the concept is very much the same, only everytime a new image is displayed. From an array of images, each image is picked up individually. After the 17th image is displayed, the counter is set to 0 again. To acquaint you with these pictures well enough, so that you can percieve the roots of animation clearly, we will now display 15 images at different coordinates.import java.applet.*; import java.awt.*; public class zzz extends Applet { Image m[]; int i=0; int a=0, b=0; int j = 1; public void init() { m = new Image[17]; for (i = 0; i<17; i++) { m[i] = getImage(getCodeBase(), "T"+j+".gif"); j++; } i=0; } public void paint(Graphics g) { g.drawImage(m[i], a, b, this); } public boolean mouseUp(Event e, int x, int y) { repaint(); i++; if (i == 17) i = 0; a = x; b = y; return true; } }
import java.applet.*;
import java.awt.*;
public class zzz extends Applet
{
Image m[];
int i, j = 1;
public void init()
{
resize(600, 400);
m = new Image[17];
for (i = 0; i<17; i++)
{
m[i] = getImage(getCodeBase(), "T"+j+".gif");
j++;
}
}
public void paint(Graphics g)
{
g.drawImage(m[0], 5, 10, this);
g.drawImage(m[1], 120, 10, this);
g.drawImage(m[2], 240, 10, this);
g.drawImage(m[3], 360, 10, this);
g.drawImage(m[5], 480, 10, this);
g.drawImage(m[6], 5, 100, this);
g.drawImage(m[7], 120, 100, this);
g.drawImage(m[8], 240, 100, this);
g.drawImage(m[9], 360, 100, this);
g.drawImage(m[10], 480, 100, this);
g.drawImage(m[11], 5, 190, this);
g.drawImage(m[12], 120, 190, this);
g.drawImage(m[13], 240, 190, this);
g.drawImage(m[14], 360, 190, this);
g.drawImage(m[15], 480, 190, this);
}
}
Now we will display the above-seen images at the same coordinates to get the effect of animation.
import java.applet.*;
import java.awt.*;
public class zzz extends Applet
{
Image m[];
int i;
int j = 1;
public void init()
{
m = new Image[17];
for (i = 0; i<17; i++)
{
m[i] = getImage(getCodeBase(), "T"+j+".gif");
j++;
}
i = 0;
}
public void paint(Graphics g)
{
g.drawImage(m[i], 50, 100, this);
}
public boolean mouseUp(Event e, int x, int y)
{
repaint();
i++;
if (i == 17)
i = 0;
return true;
}
}
The next program demonstrates what necessiates the concept of threads.
import java.applet.*;
import java.awt.*;
public class zzz extends Applet
{
int i=0;
public boolean mouseUp(Event e, int x, int y)
{
for(int k=0;k<10000;k++)
{
i++;
showStatus("i..."+i);
repaint();
}
return true;
}
public void paint(Graphics g)
{
g.drawString("i..."+i, 50, 100);
}
}
import java.applet.*;
import java.awt.*;
public class zzz extends Applet
{
int i=0;
Button b;
public void init()
{
b=new Button("hell");
add(b);
}
public boolean mouseUp(Event e, int x, int y)
{
for(int k=0;k<1000;k++)
{
i++;
showStatus("i..."+i);
repaint();
}
return true;
}
public boolean action (Event e, Object o)
{
if("hell".equals(o))
showStatus("button clicked");
return true;
}
public void paint(Graphics g)
{
g.drawString("i..."+i, 50, 100);
}
}If your mom's not calling you, get to the next chapter "Hemming our way" or harass us by mailing all your bleeding messages...