CSE 142

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Discussion Sections

Each week we will assign a written homework assignment to be turned in and discussed in section. These are meant as "warm up" problems to get you thinking about the topics we cover that week. It will be graded for effort, not for whether or not you have the right answers. You will receive 3 points for each written assignment you bring to section, up to a maximum of 20 points. The points are for the combination of completing the assignment and attending section. You won't get any points for just attending section or just doing the written assignment. As a guideline, we expect you to spend about 20 to 30 minutes on each written assignment. If you find yourself spending much more than that, then you can stop working and let your TA know that you ran out of time.

You will not be graded on whether you have a perfect solution, but on whether you have demonstrated a reasonable effort (a good guideline is that we expect you to put in half an hour of work). Therefore please show some work that demonstrates how you got the answer rather than just writing the answer by itself.

Section 9: Final practice (Thu June 2)

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 26)

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, p583). 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, p585). 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 19)

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 12)

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, p437). 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, p437). 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, p438). 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 5)

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 April 28)

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

  1. Self-Check 5.4 (while loop mystery, p378). For each method 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 tables look like this:

    mystery(19);              mystery(42);

x     y                   x     y
--------                  --------
19    0                   42    0
                          21    1
    You are to write out the tables for the other three calls. This problem is included in PracticeIt, but PracticeIt doesn't ask for the tables (just the final output). But you can still use PracticeIt to see this problem.

  2. (depends on Wednesday lecture) Programming Exercise 5.4 (randomX, p387). 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.

Section 4: if/else, Scanner, return (Thu April 21)

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

  1. Programming Exercise 4.1 (fractionSum, p314). 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, p316). 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 14)

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

  1. Parameter Mystery. Consider the following program: 
    public class Params {
    public static void main(String[] args) {
        int x = 15;
        int y = 2;
        int z = 9;

        mystery(x, y, z);
        mystery(z, x, y);
        mystery(y, z, x);
    }

    public static void mystery(int a, int b, int c) {
        System.out.println("The " + a + " monkeys ate " + (b + c) + " bananas");
    }
}
    Make a table that shows what value is being passed to each of a, b, and c for each of the three calls and then indicate the output produced by the program.

  2. Programming Exercise 3G.1 (MickeyBox, p232). 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.

Section 2: Expressions, for loops (Thu April 7)

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

  1. From Self-Check 2.3 (expressions, p119). Solve the following expressions (see note below): 
    14 / 7 * 2 + 30 / 5 + 1

(12 + 3) / 4 * 2

813 % 100 / 3 + 2.4
  2. From Self-Check 2.4 (expressions, p120). Solve the following expressions (see note below): 
    4.0 / 2 * 9 / 2

2.5 * 2 + 8 / 5.0 + 10 / 3
  3. 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 72-74). 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 Mar 31)

Written Assignment

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