**Due: Fri, Feb 11th by 11:59 PM**

Acknowledgment: The idea for this assignment comes from Christopher Stone of Harvey Mudd College.

Download CS350_Assign2.zip. Import it into your
Eclipse workspace (**File->Import...->General->Existing projects into workspace->Archive File**).
You will see a project called **CS350_Assign2** in the Package Explorer.

In this course, you are required to implement all data structures
from scratch. Do not use any of the classes in the **java.util**
package.

Exception: You may usejava.util.StringTokenizer.

Some assignments in this course may involve data structures which are implemented by source code in the textbook. And, of course, lots of code is available from web sites and other sources.

I expect you to implement all data structures and algorithms from scratch, using your knowledge of how they work. Do not copy code from any source, including the textbook.

Exception: You may use any code explicitly posted on the course web site.

You have two tasks:

- Implement a tree data structure
- Use the tree to represent "random" functions of variables
*x*and*y*

The random functions in step 2 are used to create "random art". Here's the idea

x and y values are restricted to the range -1 to 1.

The random functions are built from operations which are guaranteed to produce values in the range -1 to 1.

The random art is created by generating three random functions: one for red, one for blue, one for green. Each pixel in a square region of the GUI window corresponds to an x,y coordinate in the 2x2 region of the x/y plane centered at the origin. Each pixel's color is determined by evaluating the three functions for the pixel's x/y values, and mapping each result to the range 0..255. This produces three color component values, which together determine the overall color of the pixel.

Here is an example:

The following primitive operations can be composed to create functions which produce values in the range -1..1 (as long as x and y are in the same range):

- x
- y
*sin*(π * _)*cos*(π * _)*average*(_, _, ...)

In the above operations, the placeholder "_" is any expression built from the same operations. Thus, operations are nested recursively to represent arbitrary functions.

The random functions are represented of trees consisting
of **ExprNode** objects.

The **ExprNode** class is defined as follows:

package edu.ycp.cs350.randart; public abstract class ExprNode { // TODO: fields public ExprNode() { // TODO: initialize fields } // TODO: methods for adding and accessing child nodes /** * Evaluate the function represented by this node * for the given x and y values. * * @param x the value of the variable x * @param y the value of the variable y * @return the result of evaluating the function */ public abstract double evaluate(double x, double y); /** * Generate a textual representation of the function * represented by this node. */ public abstract String exprAsString(); }

The **evaluate** method evaluates the expression for given values
of *x* and *y*.

The **exprAsString** method returns a string containing a textual
representation of the expression.

You will need to modify this class so that child nodes can be added and accessed. You can use either a linked list or an array to store the references to the child nodes.

**Important**: I strongly recommend writing JUnit tests to test your
**ExprNode** classes. An example JUnit test class called **ExprNodeTest**
is provided; you may use this as a starting point for your tests.

Note that **ExprNode** is an abstract class. You will need to
implement concrete subclasses that represent the 5 fundamental
operations described above. The node types representing the variables
*x* and *y* will be the leaves of the overall expression tree.
The node types representing *sin*(π * _) and *cos*(π * _) expressions
will each have a single child. The node type representing
*average*(_, _, ...) expressions will have 1 or more children.

**Examples**: here are how two expressions would be represented
as trees:

Expression cos(π*x) cos(π*sin(π*avg(cos(π*cos(π*sin(π*avg(y, y, x)))), cos(π*x)))) Tree

The **ExprBuilder** class is used to generate "random" expression trees.
It is defined as follows:

package edu.ycp.cs350.randart; import java.util.Random; public class ExprBuilder { public static final int MAX_LEVEL = 8; private Random rand; public ExprBuilder() { rand = new Random(); } public ExprNode build() { throw new UnsupportedOperationException("TODO - implement"); } }

You will implement the **build** method.

The following rules should be used to build random expression trees.

**(1)** Trees must have no more than **MAX_LEVEL** levels.
The leaves of the tree are nodes representing *x* and *y*
expressions (with equal probability). All nodes added at
level **MAX_LEVEL** of the tree **must** be *x* or *y* nodes.

**(2)** For nodes at levels of the tree less than **MAX_LEVEL**,
the following probabilities should be used to determine
what kind of node to create:

- 10% chance of creating an
*x*node - 10% chance of creating a
*y*node - 20% chance of creating an
*average*(_, _, ...) node with 2 or 3 randomly-generated child expressions - 30% chance of creating a
*sin*(π * _) node with a single randomly-generated child expression - 30% chance of creating a
*cos*(π * _) node with a single randomly-generated child expression

Run the **ArtFrame** class as a Java application. The **Generate!** button
generates a new random image.

As mentioned above, you should add JUnit tests to the **ExprNodeTest** class.

You grade is determined as follows:

- Implementation of
**ExprNode**and tree operations (adding/accessing child nodes): 30% - Implementation of
**ExprNode**subclasses to represent expressions (evaluation, formatting as text): 30% - Building random expression trees: 40%

Export your finished project to a zip file (right-click on the
project, then Export...->Archive File). Upload the zip
file to the marmoset server as project **assign2**.
The server URL is

https://camel.ycp.edu:8443/

**IMPORTANT**: after uploading, you should download a copy of your
submission and double-check it to make sure that it contains
the correct files. **You are responsible for making sure your
submission is correct**. You may receive a grade of 0
for an incorrectly submitted assignment.