CSE 142: Computer Programming I, Winter 2015

Section 9: Final practice (Thu Mar 12)

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 Mar 5)

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

1. Self-Check 8.4: Reference Mystery. 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 (even if you use PracticeIt, be sure to write your answer on a sheet of paper).

2. Self-Check 8.18: Object Constructors. 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 (even if you use PracticeIt, be sure to write your answer on a sheet of paper).

Section 7: Arrays (Thu Feb 26)

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 Feb 19)

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

1. Token Based Processing. Write a static method processData that takes as a parameter a Scanner holding a sequence of integers and that reports each of the cumulative sums of the sequence along with the average of the numbers. For example, if the Scanner contains the following data:

           8 4 2 9 7 13 5 9
         

   your method should produce the following output:

           Sum of 1 = 8
           Sum of 2 = 12
           Sum of 3 = 14
           Sum of 4 = 23
           Sum of 5 = 30
           Sum of 6 = 43
           Sum of 7 = 48
           Sum of 8 = 57
           Average = 7.125
         

   Notice that the various lines of output report the sum including just the first number, then including the first two numbers, then including the first three numbers, and so on, up to the sum including all numbers. The final line of output reports the average of the sequence of numbers. Notice that this is the average of the numbers themselves, not the average of the cumulative sums.

   The amount of output will vary depending upon how many numbers are in the sequence. For example, if the Scanner contains the following values:

             1 2 3 4
           

   the method should produce the following output:

             Sum of 1 = 1
             Sum of 2 = 3
             Sum of 3 = 6
             Sum of 4 = 10
             Average = 2.5
           

   You are to exactly reproduce the format of these sample outputs. You may assume that the Scanner has at least one integer to be processed.

Section 5.5: Midterm practice (Thu Feb 12)

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 Feb 5)

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 (p369). 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 cals. 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 (p378). You can use PracticeIt to solve this problem.

Section 4: if/else, Scanner, return (Thu Jan 29)

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

1. Programming Exercise 4.1: fractionSum (p305). You can use PracticeIt to solve this problem.
2. Programming Exercise 4.12 (printTriangleType) (p307). You can use PracticeIt to solve this problem.

Section 3: parameters (Thu Jan 22)

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

1. Parameter Basics, Consider the following program:

           public class Numbers {
           public static void main(String[] args) {
           numbers(3, 1);
           numbers(4, 2);
           numbers(2, 4);
           }
           
           public static void numbers(int count, int n) {
           System.out.print(count);
           for (int i = 1; i <= count; i++) {
                                System.out.print("-" + n);
                                }
                                System.out.println();
                                }
                                }
                                

   Write down the output produced by this program.

2. 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);
           mystery(x - z, z, z);
           }
   
           public static void mystery(int x, int y, int z) {
           System.out.println("The " + x + " monkeys ate " + (y + z) + " bananas");
           }
           }
         

   Make a table that shows what value is being passed to each of x and y and z for each of the four calls and then indicate the output produced by the program.

Section 2: expressions, for loops (Thu Jan 15)

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

1. from Self-Check 2.2 (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 2.3 (p120), solve the following expressions (see note below):

   	4.0 / 2 * 9 / 2
   	2.5 * 2 + 8 / 5.0 + 10 / 3
         

3. Programming Exercise 2.6 (p128). Remember that you can use PracticeIt to solve this problem.

NOTE: For the expression problems, show how the expression is evaluated step-by-step, as is done on page 62 of the textbook. You should have a different line for each different operator that needs to be evaluated. Below is an example of what we expect:

      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 Jan 8)

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