Class Exercises
Variables
& Constants Exercises
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This
exercise should be carried out after reading the Data
Types & Variables Notes
There
are four exercises, designed to familiarize you with a variety of data types, variable declaration and
constants.
Exercise
1: Numeric Variables
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Copy
the code below into Notepad.
import java.awt.*;
public class Average {
public static void main (String[] args) {
int a;
int b;
float av;
a = 10;
b = 5;
av = (a + b)/2;
System.out.println ( "a is " + a);
System.out.println ( "b is " + b);
System.out.println ( "the average is " + av);
}
}
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Compile
and run the code. This is a Java application so you compile it as
normal:- javac
Average.java. Then run it at the command prompt using
the command:- java Average
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Now
add another variable named c and give it a value. Change the
code to display the value of c and the average of the three numbers.
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Recompile
the code and run it
Exercise
2: Numeric and String Variables
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Copy
the code below into Notepad.
//calculate area of rectangle
import java.awt.*;
import java.applet.Applet;
public class RectArea extends Applet {
public void paint (Graphics g){
String msg;
length = 100;
height = 50;
msg = "The area of my rectangle is ";
area = length * height;
g.drawRect(50, 10, length - 1, height - 1);
g.drawString (msg + area, 10, 80);
}
}
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This
code is not complete. You need to add extra code to DECLARE all the
variables.
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Compile the code.
This is a Java applet so you need to create a HTML file and then
run the applet using the browser or appletviewer. When you
have finished It should look something like this.
Exercise
3: Constants
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Copy
the code below into Notepad.
//calculate circle area & circumference
import java.awt.*;
import java.applet.Applet;
public class CircleCalc extends Applet{
public void paint (Graphics g){
circleArea = 3.14 * diameter * diameter / 4;
circumference = 3.14 * diameter;
g.drawOval(60, 0, diameter, diameter);
g.drawString("The area of my circle is " + circleArea, 0, diameter + 30);
g.drawString("The circumference of my circle is " + circumference,
0,diameter + 50);
}
}
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This
code is not complete. You need to add extra code to DECLARE all the
variables, I would suggest you use int's and doubles..
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Replace
the literal value 3.14 with a constant called PI.
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Compile the code.
his is a Java applet so you need to create a HTML file and then
run the applet using the browser or appletviewer. When you
have finished It should look something like this.
Exercise
4: Coding Practice
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Create
your own code that draws a circle and a rectangle on an applet window;
something like this.

Note:
-- Details of the graphics methods are shown below.
drawOval(int x,
int y, int width, int height)
Draws the outline
of an oval.
drawRect(int x,
int y, int width, int height)
Draws the outline
of the specified rectangle.
drawString(String
str,
int x, int y)
Draws the text using this graphics context's current color.
Note: that for the
drawrect
method, you must specify one pixel less than the desired width and height. This
is because the painting system draws lines just below the specified rectangle,
instead of within the specified rectangle. The same rule of specifying one less
than the desired width applies to other drawXxx methods,
such as draw3DRect . For the fillXxx methods,
on the other hand, you specify exactly the desired width and height in pixels.
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Have
fun!
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