CSE 142 Sp02 Final Exam Version A Page 1 of 14

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1 CSE 142 Sp02 Final Exam Version A Page 1 of 14 Basic reference information about collection classes that you may find useful when answering some of the questions. Methods common to all collection classes clear(); size(); isempty(); // remove all objects from the collection // return number of objects in collection // return true if the collection is empty Additional methods for ArrayList and HashSet add(object obj); contains(object obj); remove(object obj); iterator(); // add obj to the collection // return true if obj is in the collection // remove obj if it is in the collection // return an Iterator for the collection Additional methods for ArrayList only get(int index); // return object with given position set(int index, Object obj); // insert obj in the collection // at position index, replacing whatever // was previously there add(int index, Object obj); // insert obj in the collection // at position index, moving other items // over to make room remove(int index); // remove object at the given position Additional methods for HashMap only put(object key, Object value); // store value in the HashMap under the // given key get(object key); // return the object in the HashMap with // the given key, or null if no object // is stored under that key

2 CSE 142 Sp02 Final Exam Version A Page 2 of 14 Question 1. (16 points) Suppose that an implementation of class Fish is available to you. The Fish class has the following methods: // Constructor. name is the name of the fish (e.g., Charlie ). gramsfoodperday is the // number of grams of food the fish needs per day. (All fish eat the same food.) / ciwater is the number of cubic inches of water this fish requires to stay alive. public Fish( String name, double gramsfoodperday, double ciwater ); // Returns the fish s name public String getname(); // Returns the fish s food requirement in grams per day. public double getdailyfoodrequirement(); // Returns the number of cubic inches of water this fish requires public double getcubicinchesrequired(); Your job is to implement class Aquarium, filling in the implementation of the methods indicated below. An Aquarium object is used to keep track of the fish in an actual aquarium, to determine how much food to place in the aquarium each day, and to determine whether or not a new fish can be added to the aquarium given the amount of water it holds. For this question, implement the methods below, assuming the implementation of Fish is already completed and that a Fish accepts the messages listed above. public class Aquarium { // put any instance variables you need here // constructor client specifies the dimensions of the aquarium, in inches public Aquarium( double width, double length, double height ) {

3 CSE 142 Sp02 Final Exam Version A Page 3 of 14 // return true if the Aquarium is big enough to hold the new fish, false otherwise public boolean canaddfish( Fish proposednewfish ) { // add the given fish to the aquarium if there is room, otherwise do nothing public void addfish( Fish newfish ) { // update the Aquarium to reflect the removal of the given fish public void removefish( Fish removedfish ) { // returns the total amount of food required by all fish in the aquarium per day, in grams public double foodrequiredperday() {

4 CSE 142 Sp02 Final Exam Version A Page 4 of 14 // returns true if the specified Fish is in this Aquarium (not one with the same name, exactly // this Fish), and false otherwise public boolean hasfish( Fish searchedforfish ) { // returns a String that is the concatentation of the names of all fish in this Aquarium, // separated by blanks. (E.g., if the fish are Charlie, Bert, and Ernie, this method // would return Charlie Bert Ernie. If there are no fish in the Aquarium, it should return // empty.) public String tostring() {

5 CSE 142 Sp02 Final Exam Version A Page 5 of 14 Question 2. (4 points) Implement the method issorted below. issorted returns true if the three values are in either ascending or descending order. For instance, issorted (1,2,3) returns true; issorted (10,3,-1) also returns true; issorted (1,2,2) also returns true; issorted (10, 4, 21) returns false. public boolean issorted( int firstnum, int secondnum, int thirdnum ) { Question 3. (4 points) Briefly explain what this method does. public String stringmethod( int inputval ) { String result = ; while ( inputval > 0 ) { switch( inputval % 10 ) { case 0: result = result + 0 ; case 1: result = result + 1 ; case 2: result = result + 2 ; case 3: result = result + 3 ; case 4: result = result + 4 ; case 5: result = result + 5 ; case 6: result = result + 6 ; case 7: result = result + 7 ; case 8: result = result + 8 ; case 9: result = result + 9 ; inputval = inputval / 10; return result;

6 CSE 142 Sp02 Final Exam Version A Page 6 of 14 Question 4. (3 points) Here is a fragment of code defining class CodeExample: public class CodeExample { int instancevar; // (A) public void examplemethod() { int localvar; // (B) This fragment defines an instance variable name, instancevar, at the line labeled (A), and a local variable name, localvar, at the line labeled (B). Briefly explain the most important difference(s) between an instance variable and a local variable. For example, why would a programmer choose one or the other?

7 CSE 142 Sp02 Final Exam Version A Page 7 of 14 Question 5. (7 points) Complete the definition of method biggestinteger below so it returns the numerically largest BigInteger from the ArrayList collection bigints. If collection bigints is empty, method biggestinteger should return null. You may assumethat bigints only contains BigInteger objects, if it contains anything at all. This method doesn t use any other instance variables or methods, so it doesn t matter what class it is declared in. Several pages of Sun s JavaDocs summarizing the methods for BigInteger followthis page. Thereis also a detailed description of the BigInteger compareto method, which you may find useful in your solution. However, there is also at least one way to solve this problem without using compareto, so don t feel that you must use it in your solution (look at other BigInteger methods for ideas). /** Return the numerically largest BigInteger in bigints, or return * null if bigints is empty */ public BigInteger biggestinteger(arraylist bigints) {

8 CSE 142 Sp02 Final Exam Version A Page 8 of 14 Question 6. (4 points) The PL142 language from homework 5 included one kind of declaration and two kinds of statements, print and assignment. The syntax for these three parts of the language were: INTEGER variablename; variablename; variablename = leftoperand <op> rightoperand; where leftoperand and rightoperand could be either a variable name or an integer constant, and <op> was either + for addition or * for multiplication. If you recall from lecture, the following finite state automaton (FSA) can be used to recognize legal PL142 sentences (declarations and statements). Now suppose we want to change the PL142 print statement so it has an explicit keyword PRINT in front of the variable to be printed. This means replacing the variablename; print statement with PRINT variablename; For this question, modify the above FSA diagram so it properly recognizes statements in this modified version of PL142. You should add any new nodes and transitions that are needed, and cross out any nodes and transitions that are no longer needed to recognize the modified PL142 language.

9 CSE 142 Sp02 Final Exam Version A Page 9 of 14 Question 7. (7 points) Java provides many ways to read input from a file, but the most commonly used method to read lines from a file containing text is to use an object of class BufferedReader to represent the file. The key message that can be sent to a BufferedReader object is readline, which returns the next line from the file as a String. Here is a (slightly abbreviated) description of this method from the documentation for class BufferedReader. readline public String readline() throws Exception Read a line of text. Returns: A String containing the contents of the line, or null if the end of the file has been reached. Throws: Exception - If an error occurs while reading the file. Complete the definition of method copyfiletosystemout below so it reads all of the lines from the BufferedReader object inputfile and prints the lines on System.out. Hint: the answer only requires a few lines of code, but you may need to deal with exceptions. /** Copy lines from inputfile to System.out. */ public void copyfiletosystemout(bufferedreader inputfile) {

10 CSE 142 Sp02 Final Exam Version A Page 10 of 14 Question 8. (3 points) Here is a small program that does something with mouse clicks. What happens when it is executed? (I.e., if the user starts clicking the mouse, what will happen on the screen?) File InheritanceWindowListener.java: import uwcse.graphics.*; public class InheritanceWindowListener extends GWindowEventAdapter { private DummyClass mydummyclassobject; public InheritanceWindowListener( DummyClass d ) { mydummyclassobject = d; public void mousepressed(gwindowevent e) { mydummyclassobject.registermouseclick(e.getx(), e.gety()); File DummyClass.java: import uwcse.graphics.*; import java.awt.color; public class DummyClass { private GWindow private InheritanceWindowListener private boolean private int private int mainwindow; listener; toggle; xloc; yloc; public DummyClass() { toggle = false; mainwindow = new GWindow(); mainwindow.setexitonclose(); listener = new InheritanceWindowListener( this ); mainwindow.addeventhandler( listener ); public void registermouseclick( int x, int y ) { if ( toggle ) { mainwindow.add( new Rectangle( xloc, yloc, x-xloc, y-yloc, Color.green, true ) ); xloc = x; yloc = y; toggle =!toggle; // flip toggle from false to true or vice versa public static void main( String args[] ) { DummyClass dc = new DummyClass();

11 CSE 142 Sp02 Final Exam Version A Page 11 of 14 Question 9. (12 points) Design (but you don t have to implement) a complete program for the eyeballs program. This program creates an animation that appears to be two eyeballs looking at a moving rectangle. A single frame of the animation might look like this: In the animation, the rectangle continuously moves back and forth horizontally, from one side of the GWindow to the other. As it moves, the pupils of the eyeballs follow it. The pupils are positioned on a line that connects the center of the moving rectangle to the center of the eyeball. Here s a picture that shows these ideas, using dashed lines that are not part of what is actually drawnonthescreen:

12 CSE 142 Sp02 Final Exam Version A Page 12 of 14 As the rectangle moves back and forth on along the dashed line, the pupils move along the perimeter of the eyeball circles. Here s what things look like with the rectangle in another position: To locate the eyeballs, the following might be useful: Suppose you have a line segment connecting points (x1,y1) and (x2,y2). The length of that line segment, length, is Math.sqrt( (x1-x2)*(x1-x2) + (y1-y2)*(y1-y2) ). The point that is distance 1.0 from (x1,y1) along that line segment is ( x1 + (x2-x1)*1.0/length, y1 + (y2-y1)*1.0/length ) SUMMARY: Design an application that produces an animation like that described above. It doesn t matter exactly where the eyeballs are located, nor exactly where the imaginary line that the rectangle moves back and forth across is located pick values that will give a display that looks roughly like the above figures. FOR FULL CREDIT: Your solution should describe the program in sufficient detail that an experienced Java programmer could translate it into Java code without having to do any further design. That means you must specify each of the class(es) in your program, describe their instance variables, and describe in English each of the methods in the class and what it does. You are not required to implement your design, although you can use Java code to illustrate or clarify your design. IMPORTANT: Whether or not you find this application difficult, it makes sense to attack it in pieces. For example, first make sure you can animate a rectangle moving back and forth along a horizontal line. Then worry about drawing the eyeballs. Finally, worry about making the pupils move.

13 CSE 142 Sp02 Final Exam Version A Page 13 of 14 IMPORTANT: Take a few minutes to think about the classes you will want, and what methods they must support, before writing your final answer. Possibly useful note:both uwcse.graphics.oval and uwcse.graphics.rectangle support methods int getcenterx() and int getcentery(), which return the x and y coordinates of the shape s center respectively. Another useful note: You do not need to worry about terminating the application. Once started, it can just run forever. Another possibly useful note: You are not required to use a model-view-controller design. Use any design that makes it clear what the objects are and what messages they handle. Reminder: You are being asked to design the program, not implement it in Java code.

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