create a “tree” using recursion

| October 22, 2018

COMP 151 – Programming Assignment 2

this assignment you and your pair programming partner(s) will write a program
to generate a tree fractal, as described below. To help you, I have written a
program to generate a fractal called the Koch Snowflake. I have also given you
my code to draw the tree fractal, minus the actual code that draws the fractal.
(What it does have is the framework that gets user input and creates the frame
to draw in.)

You have until 8AM,
Thursday, March 1 to submit your program via the class website.

and your partner should submit just one program (either of you can submit).
Your program will consist of just one file,

I will describe the Koch Snowflake fractal, and I will describe it recursively.
This is a review of what I presented in class on the Koch Snowflake. A Koch
Snowflake with 0 levels of recursion is just an equilateral triangle:

In a Koch Snowflake
with one level of recursion, each side of the triangle is replaced by

Dividing the side into three
segments of equal length.

Drawing the first and third
segments unchanged.

the middle segment as the base of an equilateral triangle (facing out),
and draw the other two sides, but not the base.

This looks like


get a Koch Snowflake with two levels of recursion, the above rules are applied
to each side of the Koch Snowflake with one level of recursion. This looks like

Replacing each side in this drawing using the above rules
gives the Koch Snowflake with three levels of recursion, and it looks like


can continue to an arbitrary number of levels of recursion. My program for
generate these images is in a file called, and you can
download it from the assignment page on the class website.

When you run this
program, you are prompted to enter two parameters:

length in pixels of one side of the triangle that is the 0 levels of
recursion snowflake, and
The number of levels of
recursion to display.

you enter these values, the Koch Snowflake with 0 levels of recursion is
displayed. When you click the mouse, the Koch Snowflake with 1 level of
recursion is displayed, and when you click the mouse again, the Koch Snowflake
with 2 levels of recursion is displayed. Each mouse click increases the level
of recursion by one.
When the maximum level of recursion (the second user
parameter) is reached, the next mouse click takes the drawing back to the level
0 recursion. At any time, a double click takes you to the maximum levels of
recursion. To terminate the program, close the graphics window that shows the

the tree fractal: a tree fractal with just one level recursion is just a single
central branch:


In a tree with one
level of recursion, the level 0 tree is drawn, plus

Five branches coming off of the single
central branch, alternating left and right, starting with left at the
bottom of the tree. The branches are spread out evenly along the central
branch. In general, the number of branches coming off the central branch
is a parameter to the problem, so it does not have to be five.
Other parameters to the
problems are

length of the side branches, as a fraction of the length of the central
branch. In this drawing, the length is 0.4.
angle that the side branches make with the central branch. In this
drawing, the angle is 45 degrees.

This tree with one
level of recursion looks like

In a tree with two levels of recursion, each of the side
branches is itself treated like a central branch, and side branches are drawn
off them. The same parameters are used to draw these new branches: number of
branches, length of branches, and angle of branches. The resulting tree looks


Continuing the
recursion to three levels gives a tree that looks like

As with the Koch
snowflake, the recursion can continue indefinitely.

On the assignment page of the class website is a file that contains my solution, with the paintComponent method
removed. You should write paintComponent, along with any helper methods that
you need, so that draws the tree fractal.

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