CSE 142: Computer Programming I, Spring 2017

Section 9: Final practice (Thu June 1)

Exercises: Solve the following problem on paper and bring your sheet of paper to your section on Thursday:

1. Inheritance. Assume that the following classes have been defined:

   public class George extends Sally {
       public void method2() {
   	System.out.println("george 2");
       }
   }
   
   public class Fred {
       public void method1() {
   	System.out.println("fred 1");
       }
   
       public void method2() {
   	System.out.println("fred 2");
       }
   
       public String toString() {
   	return "fred";
       }
   }
   
   public class Harold extends Sally {
       public String toString() {
   	return "harold";
       }
   }
   
   public class Sally extends Fred {
       public void method1() {
   	System.out.println("sally 1");
       }
   
       public String toString() {
   	return "sally";
       }
   }
   

   Consider the following code fragment:

   Fred[] elements = {new Sally(), new Fred(), new George(), new Harold()};
   for (int i = 0; i < elements.length; i++) {
       System.out.println(elements[i]);
       elements[i].method1();
       elements[i].method2();
       System.out.println();
   }
   

   What output is produced by this code? (write the output as a series of 3-line columns in order from left to right)

Section 8: Objects (Thu May 25)

Exercises: Solve the following problems on paper and bring your sheet of paper to your section on Thursday:

1. Self-Check 8.4 (reference mystery, p578). The following program produces 4 lines of output. Write each line of output below as it would appear on the console.

   public class ReferenceMystery3 {
      public static void main(String[] args) {
         int a = 7;
         int b = 9;
         Point p1 = new Point(2, 2);
         Point p2 = new Point(2, 2);
         addToXTwice(a, p1);
         System.out.println(a + " " + b + " " + p1.x + " " + p2.x);
         addToXTwice(b, p2);
         System.out.println(a + " " + b + " " + p1.x + " " + p2.x);
      }
   
      public static void addToXTwice(int a, Point p1) {
         a = a + a;
         p1.x = a;
         System.out.println(a + " " + p1.x);
      }
   }
   

   You can use PracticeIt to solve this problem. If you do, be sure to write your answer on a sheet of paper.
2. Self-Check 8.18 (Object Constructors, p580). The constructor in the following class definition has two major problems. What are they? Describe the issues, and write a working version of the constructor:

   public class Point {
       int x;
       int y;
   
       // The constructor:
       public void Point(int initialX, int initialY) {
           int x = initialX;
           int y = initialY;
       }
   }
   

   You can use PracticeIt to solve this problem. If you do, be sure to write your answer on a sheet of paper.

Section 7: Arrays (Thu May 18)

Exercises: Solve the following problem on paper and bring your sheet of paper to your section on Thursday:

1. Array Simulation. You are to simulate the execution of a method that manipulates an array of integers. Consider the following method:

   public static void mystery(int[] list) {
       for (int i = 1; i < list.length - 1; i++) {
           if (list[i] > list[i - 1]) {
               list[i + 1] = list[i - 1] + list[i + 1];
           }
       }
   }
   

   Below are a list of specific lists of integers. You are to indicate what values would be stored in the list after method mystery executes if the given integer list is passed as a parameter to mystery.

   {2, 4}
   {1, 2, 3}
   {2, 2, 2, 2, 2}
   {1, 2, 2, 2, 2}
   {2, 4, 6, 8}
   

   Show your work by writing the array's initial contents and then crossing out elements and writing new values as they change.

Section 6: File input/output (Thu May 11)

Exercises: Solve the following problems on paper and bring your sheet of paper to your section on Thursday:

For the next several questions, consider a file called readme.txt that has the following contents:

6.7           This file has
          several input lines.

  10 20           30   40

test

1. Self-Check 6.12 (file processing, p433). What would be the output from the following code when it is run on the readme.txt file?

   Scanner input = new Scanner(new File("readme.txt"));
   int count = 0;
   while (input.hasNextLine()) {
      System.out.println("input: " + input.nextLine());
      count++;
   }
   System.out.println(count + " total");
   

2. Self-Check 6.13 (file processing, p433). What would be the output from the code in the previous exercise if the calls to hasNextLine and nextLine were replaced by calls to hasNext and next, respectively?
3. Self-Check 6.14 (file processing, p434). What would be the output from the code in the previous exercise if the calls to hasNextLine and nextLine were replaced by calls to hasNextInt and nextInt, respectively? How about hasNextDouble and nextDouble?

Section 5-5: Midterm practice (Thu May 4)

Exercises: Solve the following problem on paper and bring your sheet of paper to your section on Thursday:

1. Assertions. You will identify various assertions as being either always true, never true or sometimes true/sometimes false at various points in program execution. The comments in the method below indicate the points of interest.

   public static int mystery(int x) {
       int y = 1;
       int z = 0;
       // Point A
       while (x > y) {
   	// Point B
   	z = z + x - y;
   	x = x / 2;
   	// Point C
   	y = y * 2;
           // Point D
       }
       // Point E
       return z;
   }
   

   Copy the table below onto a sheet of paper and fill it in with the words ALWAYS, NEVER or SOMETIMES.

   	x > y	z > 0	y % 2 == 0
   Point A
   Point B
   Point C
   Point D
   Point E

Section 5: while, Random, boolean (Thu Apr 27)

Exercises: Solve the following three (3) Self-Check problems on paper and bring your sheet of paper to your section on Thursday:

1. Chapter 3, Self-Check Problem #20: String methods (p188 problems d, h, and l.) Consider the following variable declarations:

      String str1 = "Q.E.D.";
      String str2 = "Arcturan Megadonkey";
      String str3 = "Sirius Cybernetics Corporation";
   

   Evaluate the following expressions

     d. str2.toUpperCase()
     h. str1.indexOf(".")
     l. str3.substring(9, str3.indexOf("e"))
   

2. Chapter 5, Self-Check Problem #3: while loop mystery (p372-73).

     public static void mystery(int x) {
        int y = 1;
        int z = 0;
        while (2 * y <= x) {
           y = y * 2;
           z++;
        }
        System.out.println(y + " " + z);
     } 
   

   Write the output of the first three (3) calls -- mystery(1), mystery(6), mystery(19). Show your work by writing each value that each variable has as the code is running. For each call, make a table showing the values that x and y have as you execute the while loop for that particular call. For example, for the first two calls, the table look like this:

   mystery(1);                
   mystery(6);
   
   x     y     z              x     y     z
   _____________              _____________
   1     1     0              6     1     0
   ...                        ...
   						

3. Random: Write code that generates a random...

   • integer between 0 and 10 inclusive.

   • integer between 11 to 99 inclusive.

   • odd integer (not divisible by 2) between 50 and 99 inclusive.

Section 4: if/else, Scanner, return (Thu Apr 20)

Exercises: Solve the following problems on paper and bring your sheet of paper to your section on Thursday.

1. Programming Exercise 4.1 (fractionSum, p309). Remember that you can use PracticeIt to solve this problem. If you do, either print what you end up with so that you can turn it in or copy the code to your paper.
2. Programming Exercise 4.12 (printTriangleType, p311). Remember that you can use PracticeIt to solve solve this problem. If you do, either print what you end up with so that you can turn it in or copy the code to your paper.

Section 3: parameters, graphics (Thu April 13th)

Exercises: Solve the following two (2) problems on paper and bring your sheet of paper to your section on Thursday. Note that MysteryTouch has been modified.

1. Chapter 3, Self-Check #8, p185 (MysteryTouch), Consider the following program:

     public class MysteryTouch {
        public static void main(String[] args) {
           String head = "shoulders";
           String knees = "toes";
           String elbow = "head";
           String eye = "eyes and ears";
           String ear = "eye";
   
           touch(ear, elbow);
           touch(eye, ear);
        }
   
        public static void touch(String elbow, String ear) {
           System.out.println("touch your " + ear + " to your " + elbow);
        }
     }
   

   Make a table that shows what value is being passed to elbow and ear for both calls and then indicate the output produced by the program.
   
2. Programming Exercise 3G.1 (p227) You can see the problem and check your work at: Practice-It.
   

Section 2: Expressions, for loops (Thu April 6)

Exercises: Solve the following problems on paper and bring your sheet of paper to your section on Thursday. For expressions problems, show your work (see note below).

1. From Self-Check 2.3 (b) (expressions, p119).

   14 / 7 * 2 + 30 / 5 + 1
   

2. From Self-Check 2.4 (d) (expressions, p120).

   4 * 3 / 8 + 2.5 * 2
   

3. From Self-Check 2.5 (i) (expressions, p120).

   4 + 1 + 9 + "." + (-3 + 10) + 11 / 3
         

4. Self-Check 2.31 (for loops, p126). What is the output of the following sequence of loops?

   for (int i = 1; i <= 2; i++) {
       for (int j = 1; j <= 3; j++) {
           for (int k = 1; k <= 4; k++) {
               System.out.print("*");
           }
           System.out.print("!");
       }
       System.out.println();
   }
   

For the expression problems, please show some work rather than just writing the answer. Write out sub-expressions as you compute their values, and circle or underline operands to show precedence, as is done in the section on "Precedence" in chapter 2 of the textbook (pages 70-73). For example:

2 + 19 % 5 - 11 * (5 / 2)

2 + 19 % 5 - 11 * 2

2 + 4      - 11 * 2

2 + 4      - 22

6          - 22

-16

Section 1: Basic Java, static methods (Thu March 30)

Complete the introductory survey if you haven't done so already.