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Java by Example - random colors and arrays
This example combines nested loops, random numbers and "custom made" colors.
Since colors are defined by their Red, Green and Blue fraction, ranging from 0 to 255, we have to generate three random numbers in that range to generate random colors. In order to get a clear picture, we need to make sure the colors are not generated in the paint() method every time Java paints the applet new by default. We need a way to create 100 colors in a controlled way at a time we wish. To do this we need to introduce arrays. Arrays can hold several variables of the same type (int, float, String, Color, Font etc.) which can be accessed through one name and an index number. This makes it especially easy to access them inside a loop. Since arrays are "real" objects in Java, we have to declare them and then instanciate them with "new".
So in this program the color array is filled only once (inside the init()-method) and we use double buffering and a thread (updated 10 times a second here) to ensure everything gets drawn correctly without flicker. Instead of putting the drawing functions directly into the paint() method, we put that part into a drawColors() method, which is called from the paint() method.
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//Sourcecode
import java.awt.*;
import java.applet.*;
public class Project16 extends Applet implements Runnable
{
Image Buffer;
Graphics gBuffer;
//declare an array variable to hold our Colors
Color myColors[];
Thread runner;
public void init()
{
//create off-screen image we can draw to
Buffer=createImage(size().width,size().height);
gBuffer=Buffer.getGraphics();
//arrays are real objects, we have to declare them with "new"
myColors = new Color[100];
for(int i=0;i<100;i++)
{
int red=(int)(Math.random()*255);
int green=(int)(Math.random()*255);
int blue=(int)(Math.random()*255);
//fill our array with random colors
myColors[i]=new Color(red, green, blue);
}
}
public void start()
{
if (runner == null)
{
runner = new Thread (this);
runner.start();
}
}
public void stop()
{
if (runner != null)
{
runner.stop();
runner = null;
}
}
public void run()
{
while(true)
{
//halt the thread for 100 ms here
try {runner.sleep(100);}
catch (Exception e) { }
repaint();
}
}
public void update(Graphics g)
{
paint(g);
}
public void drawColors()
{
//draw tiles with random colors
//we use two nested loops to do this:
int i=0;
for(int x=0;x<300;x+=30)
for(int y=0;y<300;y+=30)
{
gBuffer.setColor(myColors[i]);
gBuffer.fillRect(x,y,60,60);
//increment the index of our array here
i++;
}
}
public void paint (Graphics g)
{
drawColors();
//copy the buffer to the screen
g.drawImage (Buffer,0,0, this);
}
}
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This applet adds automatic refresh of our color applet once a second, so we add a getNewColors() method, which is called once in a second, to get 100 new colors for our array.
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//Sourcecode
import java.awt.*;
import java.applet.*;
public class Project17 extends Applet implements Runnable
{
Image Buffer;
Graphics gBuffer;
//declare an array variable to hold our Colors
Color myColors[];
Thread runner;
public void init()
{
//create off-screen image we can draw to
Buffer=createImage(size().width,size().height);
gBuffer=Buffer.getGraphics();
//arrays are real objects, we have to declare them with "new"
myColors = new Color[100];
}
public void getNewColors()
{
for(int i=0;i<100;i++)
{
int red=(int)(Math.random()*255);
int green=(int)(Math.random()*255);
int blue=(int)(Math.random()*255);
//fill our array with random colors
myColors[i]=new Color(red, green, blue);
}
}
public void start()
{
if (runner == null)
{
runner = new Thread (this);
runner.start();
}
}
public void stop()
{
if (runner != null)
{
runner.stop();
runner = null;
}
}
public void run()
{
while(true)
{
//halt the thread for 1000 ms here
try {runner.sleep(1000);}
catch (Exception e) { }
//get new colors every second
getNewColors();
repaint();
}
}
public void update(Graphics g)
{
paint(g);
}
public void drawColors()
{
//draw tiles with random colors
//we use two nested loops to do this:
int i=0;
for(int x=0;x<300;x+=30)
for(int y=0;y<300;y+=30)
{
int red=(int)(Math.random()*255);
int green=(int)(Math.random()*255);
int blue=(int)(Math.random()*255);
gBuffer.setColor(myColors[i]);
gBuffer.fillRect(x,y,60,60);
//increment the index of our array here
i++;
}
}
public void paint (Graphics g)
{
drawColors();
//copy the buffer to the screen
g.drawImage (Buffer,0,0, this);
}
}
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