In this lab you will experiment with conditional
statements (if - else) and boolean expressions.
- Set up a new eclipse project for each lab (detailed instructions)
- Copy the files DrawingPanel.java, DrawLoop.java and IfGrid.java into your lab4 project folder. (One simple way to do this is to save the links to desktop, and then drag the desktop icons into the Eclipse project).
Run the DrawLoop program to make sure it works.
The DrawLoop code requires some explanation of a new
construct, the while loop, which is being used to
help make this lab more interesting. We will be learning
about loops in class soon. Loops repeatedly execute a block
of code, known as the body of the loop, which is highlighted
in bold below:
while (i < 8) { // repeat for i = 0,1,2...7
int cornerX = i*50; // calculate upper left corner
int cornerY = i*25;
g.setColor(Color.WHITE);
g.fillOval(cornerX + 5, cornerY + 5, sizeX-10, sizeY-10);
g.setColor(Color.BLACK);
g.drawRect(cornerX, cornerY, sizeX, sizeY);
i++; // increment i for next iteration
}
This loop will repeat 8 times. The value of the variable i
is 0 the first time, 1 the second time, and so on up to a
value of 7. The effect of this code is to draw 8 ovals and
eight rectangles. In this lab you will not need to change
the behavior of the loop.
You are going to be making a series of small changes.
When you are done it should look like this:
Below are the changes that you need to make. Make each
change one at a time and test it and make sure you
understand it before moving on.
- Change the background color to a new color of your
choice. I used the Red Green Blue values shown
below. Experiment and create an interesting color.
Note that the additive color model of emitted light (RGB)
may not match your color mixing intuition (red plus green
does not make brown.)
- Change the color of the ovals from all white to alternating between two colors. Specifically, replace the statement to set the color to white with:
g.setColor(Color.orange);
else
g.setColor(Color.green);
Recall that the loop changes the value of i every iteration. The expression i%2 == 0 uses the modulus operator % (a.k.a. remainder) to test if a value is even or odd. In this expression if the value of i is even, then the remainder when divided by two will be 0, but if i contains an odd value then the remainder will be 1. This is used to make the if statement alternate each iteration between the true and false cases. (Remember this even/odd test. It is very useful!)
Copy and paste a screen capture of the final drawing panel
into your solutions document. In Windows this can be
done by:
- Selecting the window you want to capture.
- Hit Alt-PrintScreen to capture an image of your window to the clipboard.
- Switch into your editor and paste it with Ctrl-V.
On the Mac :
- Command-Shift-4
- Click on one corner and drag mouse to diagonal corner
- will find the screen snapshot on the desktop and you can
insert this into your word file
Also paste your final program into your solutions document.
The rest of the exercises will use the program IfGrid.java to experiment with conditional expressions used in if statements. Run the program to make sure it works. It should produce the drawing panel shown below.
Examine the code to see how it works. It is very similar to
your program from the previous exercise. The main difference
is that there are two loops with the second loop nested
inside the first one. The behavior of these nested loops is
to create all combinations of x & y, with
0
<= x <= 9
0
<= y <= 9
The above diagram displays the x & y values in the
nested loop. As in the previous exercise, we will not modify
the loops, but we will use the x & y values that are
generated from the loops to create interesting patterns
using if statements.
Notice that inside the block associated with the loops,
there is also an if
statement that sets the color for each rectangle.
g.setColor(Color.green);
else
g.setColor(Color.yellow);
g.fillRect(cornerX, cornerY, sizeX-1, sizeY-1);
Currently the program sets the color to green for each
rectangle that has an x value of 4. This ends up
making a vertical stripe. This is in fact a model of
how pixel-based computer graphics systems work. Each
pixel is assigned a color and patterns of pixels are
modified to draw lines, shapes, and pictures.
Change the expression in the if statement so that the right
half of the rectangles (those with x >= 5) are colored
green :
Copy your modified if
statement into
your
solutions document. You don't need to copy any more
pictures for this lab.
Change the expression in the if statement to make the
diagonal green. Note the relationship between x and y
for the green squares.
Copy your modified if statement into your solutions
document.
Change the expression in the if statement to make the lower
left triangle green. Note the relationship between x
and y for the green squares.
Copy your modified if statement into your solutions document.
A little bit trickier. Change the expression in the
if statement to make the upper left triangle green.
Hint look at the sum x + y for the green squares.
Copy your modified if statement into your solutions document.
Another one. Hint look at the sums of x + y for the green squares versus the yellow squares.
Copy your modified if statement into your solutions document.
Now use a series of if -
else statements to make column 4 green, column 5
blue, column 6 red, and leave the rest yellow.
Copy your modified if statements into your solutions document.
Save this
document document to your USB flash drive, and submit it
through Brightspace.
