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You have 110 minutes to finish this test. Your exam should contain 6 problems (numbered 0-5). This is an open-book test. You may consult any books, notes, or other paper-based inanimate objects available to you. Read the problems carefully. If you find it hard to understand a problem, please ask a question. Please write your answers in the spaces provided in the test; if you need to use the back of a page make sure to clearly tell us so on the front of the page.
Good Luck!
0 out of 1 point
1 out of 2 points
2 out of 6 points
3 out of 3 points
4 out of 3 points
5 out of 9 points
Total out of 24 points
Question 1 (2 points) Below is a class that creates a geometric shape. Draw a picture of what memory looks like at the spot indicated in the main method. Note: The Point class has instance variables x and y of type int.
import java.awt.Point;
public class GeometricShape { public Point[] vertices; int sides; public GeometricShape(int[] xValues, int [] yValues) { sides = xValues.length; vertices = new Point[6]; for (int i = 0; i < sides; i ++){ vertices[i] = new Point(xValues[i], yValues[i]); } } public static void main(String [] args){ int[] myXs = {0, 2, 2, 0}; int[] myYs = {0, 0, 5, 5}; GeometricShape shape = new GeometricShape (myXs, myYs); // DRAW A PICTURE OF WHAT MEMORY LOOKS LIKE HERE!!! } }
main
myXs
myYs
shape
Please write your solution to Question 2 here:
Question 3 (3 points)
Now we are going to test ExpandableSet using JUnit. When we change the length of ExpandableSet, we want it to become exactly the length we expect. For example, if the ExpandableSet should have doubled in length we want it to be exactly double the length, no more, no less.
a) However in the JUnit file we can’t just check the length of the array. Explain why.
b) Complete the helper method below to appear in your JUnit file ExpandableSetTest. This method will return true if the length of the ExpandableSet es is equal to the int expectedSize. You may not write any additional methods. Hint: It will be helpful to use the concept of Exceptions.
public class ExpandableSetTest extends TestCase {
private boolean sizeCheckHelper(ExpandableSet es, int expectedSize){
Question 5 (9 points)
This question is based upon Project 1. Relevant details of the Picture class and Pixel class are provided on the next few pages. The goal is to iterate over all Pixels in a Picture that are within a Circle. The order in which Pixels are returned doesn’t matter, but all Pixels within the circle should be returned. For example, we want to be able to run the following method in the Picture class:
// Colors the picture with a black circle of radius 10, // centered at (50, 50) public void blackCircle(){ this.initIterator(50, 50, 10); while (this.hasNext()){ this.next().setColor(new Color(0, 0, 0, 255)); } }
Based upon the comments below, implement the following methods for the Picture class. You may only add code within the methods defined below. Any other modifications will result in a score of 0 on this question.
public class Picture extends SimplePicture { // instance variables – You may NOT define any new instance variables
int midX; // the X coordinate of the center of the circle int midY; // the Y coordinate of the center of the circle int radius; // the radius of the circle Pixel nextPixel; // Invariant : always references the next Pixel to // be returned by next() or null if no // pixels remain.
// Returns true if there are more pixels to return in the circle // and false otherwise public boolean hasNext() { // if nextPixel is null, there are no more pixels to return return nextPixel != null; }
// HELPER METHOD // Returns true if the instance variable nextPixel is within the // the circle and false otherwise. private boolean isNextPixelWithinRadius() { if (nextPixel == null) { return false; } int x = nextPixel.getX(); int y = nextPixel.getY(); return (Pixel.distance(x, y, midX, midY) < radius); }
// This method should restore the invariant described for nextPixel. // You must call this method at least once in your code on the next page. // This method may call the optional helper method getUnexploredPixel private void restoreInvariant() {
// OPTIONAL HELPER METHOD
// If you chose to implement this method you must implement exactly what // the comment specifies. // // This method should return the next unexplored Pixel based upon the // argument lastPixel. Unexplored Pixels should be returned regardless of // whether they are within the circle. This method does not modify // nextPixel. The method returns the next Pixel to be explored or null // if no unexplored Pixels remain. public Pixel getUnexploredPixel(Pixel lastPixel) {
- The Picture class has the following relevant methods */
// returns the number of pixels that the image is wide. public int getWidth()
// returns the number of pixels that the image is tall. public int getHeight()
// returns the pixel at the location (x, y) public Pixel getPixel(int x, int y)
/*
- The Pixel class has the following relevant methods */
// returns the X coordinate of the current Pixel public int getX()
// returns the Y coordinate of the current Pixel public int getY()
// sets the color of the current Pixel to be newColor public void setColor(Color newColor)
// calculates the distance between two points (x1, y1) and (x2, y2). public static int distance(int x1, int y1, int x2, int y2)
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You may use it for extra space. If you expect it to be graded you must indicate so clearly on the relevant problem.
