Jam 4: Study Guide

Jams are open book. 40 minutes in lab.

Topics:

This quiz includes the previous topics from Jams 1, 2 and 3 plus

  • classes

    • defining and using classes

    • terms: methods, member variables, accessors (getters), mutators (setters)

    • scope of member variables

  • Reading text files

  • Linear and binary search

Write Java programs to check your answers. Or you can ask a TA or instructor to give feedback on your responses.

Practice questions

1) Loop practice. Use loops to compute quantities over random numbers.

  • Using a loop, compute the sum of 5 random numbers between -10 and 10. Output the results to the console. Below is an example

9.732847
3.099474
-9.973539
2.9620247
-6.101103
Sum: -0.28029633

  • Using a loop, compute the maximum value of 5 random numbers between -10 and 10.

3) Function practice. Write functions corresponding to the following specifications. For each question, test your function from main using an array of random values as input. Your function should not hard-code the length of the array. You should also print the result to the console.

  • Write a function that converts miles to kilometers. There are 1.609 kilometers in a mile. Test your function with the following sequence of values using a loop: 1.0, 1.25, 1.5, 1.75, 2.0, …​, 3.0.

// Implement function: milesToKilometers
// Input: miles (double)
// output: kilometers (double)

  • Write a function that computes the tip.

// Implement function: computeTip
// Input: total cost (double)
// Input: tip percent (double)
// Output: double

  • Write a function that computes the average of an array of numbers

// Implement function: computeAverage
// Input: values (array of double)
// Output: double

  • Write a function that returns true if an array of double has a negative number on it.

// Implement function: containsNegative
// Input: values (array of double)
// Output: boolean

  • Write a function that reverses the contents of an array. (Hint: create and return a new array in the function)

// Implement function: reverseArray
// Input: values (array of double)
// Output: values (array of float)

6) A programmer has a bug in her code. She expected compute to return 4.0 but it’s returning 3.0. What’s wrong?

class Mystery {
  public static float compute(float a, float b, float c) {
    float tmp = a + b;
    return tmp - c;
    tmp += 1.0;
  }

  public static void main() {
    float result = compute(1.0, 4.0, 2.0);
    System.out.println(result);
  }
}

7) Consider the following program

class Mystery {
  public static int mystery(int[] values) {
    int total = 0;
    for (int i = 0; i < values.length; i++) {
      int value = values[i];
      if (values[i] < 0) {
        value = -value;
      }
      total += value;
      System.out.println("mystery: ", value, total);
    }
    return total;
  }

  public static void main(String[] args) {
    int[] values = {-1, 0, 1, 2, 3};
    System.out.println("Checkpoint 1:", values[2]);

    int result = mystery(values);
    System.out.println("Checkpoint 2: ", result);
  }
}

  • What is the output of this program?

  • What local variables are in scope in main()?

  • What local variables are in scope in mystery()?

  • What is the return type of mystery()?

8) Consider the following program

class Mystery {
  public static String snaf(int a) {
    if (a < 5) {
      return "pop";
    }
    else {
      return "crackle";
    }
  }

  public static int fee(int q) {
    return -q;
  }

  public static int bar(int u, int v) {
    return -10*u + fee(v);
  }

  public static int foo(int x, int y) {
    return x*10 - fee(y);
  }

  public static void main(String[] args) {
    int a = -5;
    int b = 5;
    int c = 10;
    int d = foo(a, b);
    int e = bar(b, a);
    String result = snaf(d+e);
    System.out.println(result, d, e, d+e);
  }
}

  • What console output is produced by this program?

10) Consider the following program

class Main {
  public static void main(String[] args) {

    Mystery m1 = new Mystery(4,1);
    Mystery m2 = new Mystery(1,1);

    int result1 = 0;
    int result2 = 0;
    result1 = m1.compute(2);
    result2 = m2.compute(2);
    System.out.println("BEFORE compute1: ", result1);
    System.out.println("BEFORE compute2: ", result2);

    m1.setA(3);
    m2.setB(3);

    result1 = m1.compute(2);
    result2 = m2.compute(2);
    System.out.println("AFTER compute1: ", result1);
    System.out.println("AFTER compute2: ", result2);
  }
}

where Mystery is defined as

class Mystery {

  int a = 0;
  int b = 0;

  Mystery(int x, int y) {
    a = x;
    b = y;
  }

  void setA(int x) {
    a = x;
  }

  void setB(int y) {
    b = y;
  }

  int compute(int factor) {
    return a + factor*b;
  }
}

  • What is the console output of this program?

  • What constructors are defined in this program?

  • What member variables are defined in this program?

  • What variables are in scope in Mystery’s compute method?

  • What methods are defined in Mystery?

  • Implement an accessor method for the attribute (e.g. member variable) a in Mystery.

11) Write a function that takes a String as an input and replaces all occurrences of the letter e to 3 and all occurrences of the letter s to 5. Test your function from main using the phrases "elephant" and "sour patch kids".

// Function: replaceChars
// Input: initialString (String), the original string to modify
// Output: (String), the modified String

12) Write a function that takes a String as an input and returns the reverse String.

13) What would the output of the following code be?

for (int i = 0; i < 2; i++)
{
    for (int j = 0; j < 3; j++)
    {
        println("i:" + i + " j:" + j);
    }
}

19) For each iteration of the loop in binarySearch(int x, int[] L), show the index values for low, high, and mid, and the value stored at location mid. What will be returned by this function call?

int x = 67;
int[] L = {10, 12, 14, 21, 37, 44, 45, 46, 58, 67, 99};
            0   1   2   3   4   5   6   7   8   9  10

low | high | mid | L[mid]
- - - - - - - - - - - - -
    |      |     |
    |      |     |
    |      |     |
    |      |     |

20) For each iteration of the loop in binarySearch(int y, int[] L), show the index values for low, high, and mid, and the value stored at location mid. What will be returned by this function call?

int y = 4;
int[] L = [10, 12, 14, 21, 37, 44, 45, 46, 58, 67, 99];
            0   1   2   3   4   5   6   7   8   9  10

low | high | mid | L[mid]
- - - - - - - - - - - - -
    |      |     |
    |      |     |
    |      |     |
    |      |     |

21) Write a function to return the index of the smallest item in a given list.

// Input:  An array of integers
// Returns: The index of the smallest item in the list,
//    -1 if the list is empty

int indexOfSmallest(int[] ls) {
   // complete this function
}