Java Programming Assignment: Drawing Shapes with Turtle in JFrame - Prof. D. Gries | Assignments Computer Science

Assignment A5 CS1110 Fall 2008 See CMS for deadline

This assignment introduces you to graphics. You will write procedures that draw interesting designs,

bouncing balls, and a recursive design in a JFrame. You may work with one other person. If you do so,

form your group on the CMS WELL BEFORE YOU SUBMIT YOUR FILES. Remember, partners should

work together and not independently.

You need not use a JUnit testing class. You will (partly) be looking at visual output (graphics) to determine

correctnesss.

Please keep track of the time you spend on this assignment. You will be asked to put it in a comment at the

top of file A5.java.

To save time and effort, we give you complete specifications of most of the methods you write. Please study

them carefully. Note how precise and thorough they are. You should aim for this quality of specification

when you write your own specifications. At the end of this document, we tell you what to submit.

Download file A5.zip , unzip it, and put everything in it into a new directory. It contains:

1. A file A5.java, which extends class Turtle.

2. Several .class files. These are machine language versions of .java files. Do NOT load them

into DrJava. The only thing you should load into DrJava is file A5.java. It will automatically

use the .class files.

3. A directory doc, which contains specifications of classes Turtle and HSV. You will use these

specs when writing method calls to make turtles do what you want.

A Turtle is a pen of a certain color at a pixel (x, y) that is pointing in some direction given by an angle (0

degrees is to the right, or east; 90 degrees, north; 180 degrees, west; and 270 degrees, south). When the

turtle is moved to another spot using procedure moveAhead or moveBack, a line is drawn if its pen is

currently "down" and nothing is drawn if its pen is "up". The pen is initially black, but its color, of class

java.awt.Color, can be changed. A footnote on page 1.5 of the ProgramLive CD contains information

about class Color.

Open doc/index.html in your favorite browser and study the specifications of methods in class Turtle

(the javadoc files). Here are some important points:

Class Turtle uses the Graphics object that is attached to a JPanel. It builds on class Graphics by

maintaining the "turtle", which has a position and an angle and holds a pen of a color; the pen is up

or down. You can use many turtles at the same time; they all use the same JPanel.

The coordinates and angle of the turtle are maintained using type double. This is needed for

maximum accuracy. If we used int, errors might crop up after many calculations. However, whenever

a point is to be placed in the window, its x- and y- coordinates are rounded to the nearest integer

because the graphics space works with ints.

Class Color is in package java.awt. Its objects are colors in the RGB model. Take a look at its API

spec. It has various constants that you can use, e.g.put java.awt.Color.red in the DrJava

interactions pane, hit key Enter-return, and see what happens.

Manually resizing the JFrame window also changes the size of the panel on which the drawing occurs.

But you have to move the mouse inside the panel to see this.

Procedure jumpTo(ang, x, y) can be used to move the turtle, without drawing, to (x, y) and face it

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Assignment A5 CS1110 Fall 2008 See CMS for deadline This assignment introduces you to graphics. You will write procedures that draw interesting designs, bouncing balls, and a recursive design in a JFrame. You may work with one other person. If you do so, form your group on the CMS WELL BEFORE YOU SUBMIT YOUR FILES. Remember, partners should work together and not independently. You need not use a JUnit testing class. You will (partly) be looking at visual output (graphics) to determine correctnesss. Please keep track of the time you spend on this assignment. You will be asked to put it in a comment at the top of file A5.java. To save time and effort, we give you complete specifications of most of the methods you write. Please study them carefully. Note how precise and thorough they are. You should aim for this quality of specification when you write your own specifications. At the end of this document, we tell you what to submit. Download file A5.zip, unzip it, and put everything in it into a new directory. It contains:

A file A5.java, which extends class Turtle.
Several .class files. These are machine language versions of .java files. Do NOT load them into DrJava. The only thing you should load into DrJava is file A5.java. It will automatically use the .class files.
A directory doc, which contains specifications of classes Turtle and HSV. You will use these specs when writing method calls to make turtles do what you want. A Turtle is a pen of a certain color at a pixel (x, y) that is pointing in some direction given by an angle ( degrees is to the right, or east; 90 degrees, north; 180 degrees, west; and 270 degrees, south). When the turtle is moved to another spot using procedure moveAhead or moveBack, a line is drawn if its pen is currently "down" and nothing is drawn if its pen is "up". The pen is initially black, but its color, of class java.awt.Color, can be changed. A footnote on page 1.5 of the ProgramLive CD contains information about class Color. Open doc/index.html in your favorite browser and study the specifications of methods in class Turtle (the javadoc files). Here are some important points: Class Turtle uses the Graphics object that is attached to a JPanel. It builds on class Graphics by maintaining the "turtle", which has a position and an angle and holds a pen of a color; the pen is up or down. You can use many turtles at the same time; they all use the same JPanel. The coordinates and angle of the turtle are maintained using type double. This is needed for maximum accuracy. If we used int , errors might crop up after many calculations. However, whenever a point is to be placed in the window, its x- and y-coordinates are rounded to the nearest integer because the graphics space works with int s. Class Color is in package java.awt. Its objects are colors in the RGB model. Take a look at its API spec. It has various constants that you can use, e.g.put java.awt.Color.red in the DrJava interactions pane, hit key Enter-return, and see what happens. Manually resizing the JFrame window also changes the size of the panel on which the drawing occurs. But you have to move the mouse inside the panel to see this. Procedure jumpTo(ang, x, y) can be used to move the turtle, without drawing, to (x, y) and face it

at angle ang. Call pause(p) to pause execution for p milliseconds. Judicious use of this method will allow you to watch something being drawn in slow motion. Class A5.java contains procedure drawTwoLines to show you how graphics works. After compiling class A5, in DrJava's interaction pane, create an instance of class A5 and execute a call on drawTwoLines. A JFrame should be created and two lines should be drawn on it. Notice how the body of the procedure saves the initial color of the pen and ends by changing the pen back to its initial color. Generally, methods will attempt to leave things the way they were when they started, and this indicates how to do that. In the interactions pane (or in a method in class A5), draw some lines, rectangles, circles, etc, to familiarize yourself with class Turtle. After that, perform the tasks given below. Task 1. Complete function A5.toString. Follow the instructions given in the function itself. You will see why in Task 2. Here is an example of what our toString function produces, and yours should be similar: pos. (250, 250), facing 0.0 degrees, color java.awt.Color[r=0,g=0,b=0], pen down. Your output does not have to be precisely like this, but it should contain the same information, and in this order. Note: class Color has its own toString function. Task 2. Complete procedure drawRedTriangle. Then follow the instructions in the comment in the body to learn about rounding errors when using type double and why they don't really matter here. Note that the comment asks you to put some information at the topf of file A5.java (as a comment). Task 3. Complete drawRedHex to draw a red hexagon, as shown to the right of this paragraph. It should call procedure drawRedTriangle 6 times. Some lines will be drawn twice, but that is OK. Of course, when the procedure call terminates, the turtle's properties (position, angle, pen color, and whether the pen is up or down) should be the same as when the procedure call began. The procedure should draw the shape at the turtle's current position and at the turtle's current angle. Don't move the turtle before beginning. Also, note that THIS PROCEDURE DOESN'T HAVE TO DRAW ANY EXTRA LINES OR JUMP AROUND AT ALL. Just use calls on drawRedTriangle and addAngle. Task 4. Do TWO (repeat, 2) of 4A, 4B, or 4C. After you have completed the assignment, if you are interested, do the other one! It is fun, seeing how easy it is to do these neat things. Task 4A: Draw a spiral. The first picture to the right is done by drawing 10 lines. The first line has length 5; the second, 10; the third, 15, etc. After each line, 90 degrees is added to the angle. The second diagram to the right shows a similar spiral but with 75 degrees added to the angle after each line. Complete procedure spiral. When you first test your method, use 5 for d and 0 for sec. Try different angles, like 90 degrees, 92 degrees, 88 degrees, etc. You can also use msec = 500 or msec =1000 (which is 1 second) in order to see the lines drawn one at a time. You will be amazed at what method spiral does. Find out by trying these calls, assuming that x is an instance of A5. Use procedure moveToCenter() to erase the panel and place the turtle in the middle before

Move the ball, as follows: (1) draw the ball with a white pen; (2) move the turtle; and (3) draw the ball in its original color. (So, the program must remember the original color. Have a local variable origColor to contain the original color and, after drawing the ball white, set the turtle color back to the value of variable origColor.)
After moving the ball: negate the y-coordinate speed (using vy= –vy;) IF either (1) the vertical motion is negative and the ball just touches or goes partially over the top of the panel or (2) the vertical motion is positive and the ball just touches or goes partially over the bottom of the panel. You have to do the same kind of thing for the horizontal direction. Test method moveOnce() carefully, as follows. In the interactions pane, create a ball of radius 45 that starts in the middle of the panel and has velocity (0, –35). Then, repeatedly execute d.moveBallOnce() and watch what happens. Makes sure that it bounces properly off the top and bottom walls. Then do the same kind of test for the left and right walls. You will notice that, because of the way moveOnce works, the ball may partially go through a wall and then come out. That is alright. That is the way we want it. (d) Complete procedure perpetua2l(). Its body should be a loop that does not terminate and that has a repetend that (1) moves balls b1 and b2 once and then (2) pauses for 100 milliseconds. In the interactions pane, create two new Ball d1 and d2, call A5.perpetual2(d1, d2);, and watch the balls move. Stop this execution by hitting the DrJava reset button. Task 6. Recursive graphics. We now ask you to develop a recursive procedure to draw some graphics, recursively. We discuss one example, the Koch snowflake. Then, we ask you to develop a recursive procedure. We give you some examples. Directly to the right is a triangle. It is called a "Koch snowflake " of level 0. Replacing each line of this Koch snowflake by four lines as drawn in the second diagram gives the Koch snowflake of depth 1, which is the third figure. And, replacing each of the lines of this Koch snowflake by the same four lines gives the Koch snowflake of depth 2 shown on the extreme right. This can be continued to any depth. Doing this is extremely easy using recursion! This is done using procedures Koch and KochL, which appear in the class A5 that we give you. Procedure Koch is always the one to call (KochL is private), for it clears the window, etc., in preparation for drawing the Koch flake. Koch calls KochL. We can explain in a simple way what Koch and KochL using the following two patterns : Koch: L – – L – – L KochL: L + L - - L + L Here's how to interpret each of them. Each symbol is a command to do something, as follows. L: If d (depth of recursion) is 0, draw a line of length F; otherwise, call KochL(d-1, F, s). +: add 60 degrees to the turtle's angle.

: subtract 60 degree from the turtle's angle. So, the patterns are simply a simple, terse, way of describing what each of the method bodies should do. Compare these sequences of commands to the bodies of the method bodies, and you will see what we mean. Such a system of patterns is called a "Lindenmayer System", after Aristid Lindenmayer, who co-authored a book titled The Algorithmic Beauty of Plants (Springer Verlag, 1990).

In this task 6, your job is to write a procedure that draws a recursive graphical design. You can choose from a few alternatives given below. Before we begin, make careful note of these ground rules:

Following the Koch-snowflake pattern, write two procedures, a public one that will initialize as procedure Koch does and a private one, which is recursive.
Give complete and precise specifications of both procedures.
Our examples below show you output for depths 0, 1, and 2. We expect you to test your procedures with greater depth than that! And we are sure you will, because it's fun to see the graphic output appear.
Do not search the web to find procedures already written in other languages; that is dishonest. Instead, use the material given below to help you and do some problem solving of our own. Ask Gries, a TA, or a consultant for help if you need it. 1. Square flakes. Directly to the right is a square. It is called a "flake" of depth 0. Replacing each line of this flake by four lines as drawn in the second diagram yields a flake of depth 1, which is the third figure. Replacing each of the lines of this flake by the same four lines yields the flake of depth 2 shown on the extreme right. It looks like there are loops in this diagram, but that is only because two corners touch at the same point. 2. Sierpinski triangles. Directly to the right is a filled-in equilateral triangle. We call it a Sierpinski triangle of size s (the length of a side) and depth 0. Next to it is a Sierpinski triangle of size s and depth 1. It is created by filling in 3 Sierpinski triangles of size s/2. and depth 0, in each of the corners of what would be a Sierpinski triangle of size s and depth 0. All the way on the right is a Sierpinski triangle of size s and depth 2; it is created by drawing 3 Sierpinski triangles of size s/2.0 and depth 1. In the same way, draw a Sierpinski triangle of size s and depth d by drawing three Sierpinski triangles of size s/2.0 and depth d-1 in appropriate places. Here are some hints. (1) You can write the Sierpinski procedures with (at least) two parameters (x, y) that give the position of the left point of the base line of the triangle. Or, you can let the turtle indication this position. It is up to you. (2) Use procedure fillTriangle (in class A5) to draw a triangle —it is needed only at depth 0! (3) The most difficult part may be finding the height of the triangle with side length s. Knowing that the triangle is an equilateral triangle, you can make use of the pythagorean theorem to figure this out. Using h for the height, you should be able to visualize a triangle that is 1/2 of the equilaterial triangle, with side lengths s, s/2.0, and h. Solve the formula s2 = (s/2)2 + h**2 for h. 3. Sierpinski carpet. To the right are three Sierpinski carpets of depth 0, 1, and 2. Here's how you draw them: (0) Draw a black filled- in square of side length s.

Java Programming Assignment: Drawing Shapes with Turtle in JFrame - Prof. D. Gries, Assignments of Computer Science

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