Midterm Review Questions (with Answers)

The midterm exam will be broken into two components:

• A lab-based portion, on October 19, 2017
• A written (lecture-based) portion, on October 24, 2017

The lab-based portion will require you to write code on the lab machines, which is to be turned in via Canvas by the end of the class. It will be similar in style to the rest of the assignments in the course. You may NOT reference your previous submissions, and you may NOT access the Internet for any reason other than to submit your solution via Canvas. Violations of these rules will result in a 0 on the exam.

The written portion will require you to read and understand code, as well as answer short-answer questions related to programming. You may also be asked to write short amounts of code.

For both portions of the exam, you may bring in a single 8 1/2 x 11 inch sheet of paper containing handwritten notes, and you may write on both sides of the paper. If you so choose, you can bring in a different sheet of paper for each portion of the exam (they are on separate days, and you can keep it).

The review below, in addition to everything you wrote for your labs, is intended to be comprehensive. All topics which could potentially be on the exam are somehow covered by this review.

Questions

1. What is the output of the following code?

   int x = 7;
   if (x > 8) {
     System.out.println("Hello");
   } else if (x < 10) {
     System.out.println("Something: " + x);
   } else {
     System.out.println("Goodbye");               
   }
   

   Something: 7
   

2. What is wrong with the following code, if anything?

   public static void foo(int x) {
     if (x == 8) {
       System.out.println(x);
     } else {
       System.out.println(42);
     }
     return 12;
   }
   

   Cannot return a value from a method with a void return type.
   

3. Write a call to a method named blah with the parameters 5 and 6.

   blah(5, 6)
   

4. What is wrong with the following code, if anything?

   public static int doSomething(int input) {
     switch (input) {
     case 1:
       return 2;
     case 2:
       return 3;
     }
   }
   

   Possible for this method not to return anything, even though it's supposed to return an int.
   For example, if the input is 4, no case will match.
   

5. What does the following method return underneath the input 1?

   public static int compute(int input) {
     int retval = 0;
     switch (input + 1) {
     case 0:
       retval++;
     case 1:
       retval += 2;
     case 2:
       retval += 3;
     case 3:
       retval += 6;
       break;
     case 4:
       retval += 12;
     }
     return retval;
   }
   

   9
   

6. What is wrong with the following code, if anything?

   public static void baz(int input) {
     if (input == 27) {
       return;
     } else {
       System.out.println(input);
     }
   }
   

   No problems (return without a value can be used for void methods).
   

7. What is wrong with the following code, if anything?

   public static int[] qwerty(int[] input) {
     return input[0];
   }
   

   qwerty is supposed to return an array of integers (int[]), but instead it returns an int (input[0] gets an int).
   

8. Define a method named add3 which takes three ints as parameters and returns their sum.

   public static int add3(int x, int y, int z) {
     return x + y + z;
   }
   

9. What is the output of the following code?

   int[] a = new int[]{5, 4, 3, 2};
   for (int x = 0; x < a.length - 1; x++) {
     System.out.println(a[x] + 1);
   }
   

   6
   5
   4
   

10. What is the output of the following code?

    int[] b = new int[]{9, 8, 7};
    for (int x = b.length - 1; x >= 0; x--) {
      System.out.println(b[x]);
    }
    

    7
    8
    9
    

11. What is wrong with the following code, if anything?

    int[] c = new int[0];
    for (int x = 0; x <= c.length; x++) {
      System.out.println(c[x]);
    }
    

    Goes out of bounds.
    The condition should be x < c
    

12. What is the output of the following code?

    int x = 3;
    int y = 6;
    int z = 10;
    if (x > 2) {
      if (y < 8) {
        if (z > 5) {
          System.out.println(1);
        }
      } else {
        System.out.println(2);
      }
    } else {  
      System.out.println(3);
    }
    

    1
    

13. What is the output of the following code?

    int x = 0;          
    while (x < 5) {
      boolean b = false;
      if (x == 2) {
        b = true;
      }
      System.out.println(b);
      x++;
    }
    

    false
    false
    true
    false
    false
    

14. What is the output of the following code?

    int x = 0;          
    while (x < 5) {
      System.out.println("hi");
      x = 100;
      System.out.println("bye");
    }
    

    hi
    bye
    

15. Write a method named randomOneThroughTen that returns a random number between 1 and 10, inclusive (i.e., both 1 and 10 are themselves possible numbers). Do not use a seed value.

    public static int randomOneThroughTen() {
      Random r = new Random();
      return r.nextInt(10) + 1;
    }
    

16. Write a method named otherRandomOneThroughTen that returns a random number between 1 and 10, inclusive (i.e., both 1 and 10 are themselves possible numbers). otherRandomOneThroughTen takes a seed value as a parameter, and this seed value should be used as the initial value for random number generation.

    public static int otherRandomOneThroughTen(long seed) {
      Random r = new Random(seed);
      return r.nextInt(10) + 1;
    }
    

17. What is wrong with the following code, if anything?

    public static void something(int x) {
      int x = 27;
      System.out.println("42");
    }
    

    x is already declared as a parameter; both declarations of x are in the same scope.
    

18. What does the following code print, assuming it is run in jGrasp with jGrasp's “Run“ command?

    public static void useX1(int x) {
      x = 5;
      System.out.println(x);
    }
    public static void useX2(int x) {
      useX1(x);
      System.out.println(x + 1);
      x = 8;
    }
    public static void main(String[] args) {
      int x = 42;
      useX2(x);
      System.out.println(x);
    }
    

    5
    43
    42
    

19. List the types of the following expressions. If the expression has no type (it is ill-typed, so it'd produce a compile-time error), say so.
    • 5 + 3
    • 5l + 3
    • "42"
    • "42" + 1
    • 5 + 5.2
    • 5.2 + 5l
    • "hi" + true
    • 1 + true
    • 5 + 3: int
    • 5l + 3: long
    • "42": String
    • "42" + 1: String
    • 5 + 5.2: double
    • 5.2 + 5l: double
    • "hi" + true: String
    • 1 + true: Error
20. List the values produced by the following expressions.
    • 5 - 2
    • 5 * 2
    • 5 / 2
    • 5 % 2
    • 6 - 2
    • 6 * 2
    • 6 / 2
    • 6 % 2
    • 5.0 - 2
    • 5.0 * 2
    • 5.0 / 2
    • 6.0 - 2
    • 6.0 * 2
    • 6.0 / 2
    • 5 - 2.0
    • 5 * 2.0
    • 5 / 2.0
    • 6 - 2.0
    • 6 * 2.0
    • 6 / 2.0
    • 5 - 2: 3
    • 5 * 2: 10
    • 5 / 2: 2
    • 5 % 2: 1
    • 6 - 2: 4
    • 6 * 2: 12
    • 6 / 2: 3
    • 6 % 2: 0
    • 5.0 - 2: 3.0
    • 5.0 * 2: 10.0
    • 5.0 / 2: 2.5
    • 6.0 - 2: 4.0
    • 6.0 * 2: 12.0
    • 6.0 / 2: 3.0
    • 5 - 2.0: 3.0
    • 5 * 2.0: 10.0
    • 5 / 2.0: 2.5
    • 6 - 2.0: 4.0
    • 6 * 2.0: 12.0
    • 6 / 2.0: 3.0
21. What is wrong with the following code, if anything?

    public static int p1(int x, int y) {
      return x + y;
    }
    public static void main(String[] args) {
      p1(5);
    }
    

    p1 takes two int arguments, but only one is provided in the call in main.
    

22. What is wrong with the following code, if anything?

    public static int p2(int x) {
      return x;
    }
    public static void main(String[] args) {
      p2(5, 6);
    }
    

    p2 takes one int argument, but two are provided in the call in main.
    

23. What is wrong with the following code, if anything?

    public static String p3(String x) {
      return x;
    }
    public static void main(String[] args) {
      p3(5);
    }
    

    p3 takes a String argument, but an int argument is passed in main.
    

24. What is wrong with the following code, if anything?

    public static String p4(int x) {
      return x;
    }
    

    p4 tries to return an int, but it's supposed to return a String based on its declaration.
    

25. What is wrong with the following code, if anything?

    public static int p5(int x) {
      return Integer.parseInt(x);
    }
    

    Integer.parseInt takes a String, but it's being passed an int
    

26. Write a method named firstPlusLast that will take an array of integers and return the sum of the first and last integers. For example, if the first integer in the array is 3 and the last integer is 5, then it should return 8. If the array only contains one element (e.g., 7), then the first and last integer in that array is the same (so for 7, it should return 14). If the array is empty, it should return 0.

    public static int firstPlusLast(int[] a) {
      if (a.length == 0) {
        return 0;
      } else {
        return a[0] + a[a.length - 1];
      }
    }
    

27. Convert the following for loop into a while loop.

    for (int x = 0; x < 10; x++) {
      System.out.println(x);
    }
    

    int x = 0;
    while (x < 10) {
      System.out.println(x);
      x++;
    }
    

28. Convert the following while loop into a for loop.

    int x = 10;
    while (x > 7) {
      System.out.println(x);
      x--;
    }
    

    for(int x = 10; x > 7; x--) {
      System.out.println(x);
    }
    

29. Convert the following for loop into a do...while loop.

    for (int x = 0; x != 3; x++) {
      System.out.println(x);  
    }
    

    int x = 0;          
    do {
      System.out.println(x);
      x++;
    } while (x != 3);
    

30. For each loop below, state the number of iterations each loop will perform. If the loop is an infinite loop, state “infinite”.
    • for (int x = 0; x < 5; x++) { ... }
    • for (int x = 0; x < 6; x += 2) { ... }
    • for (int x = 5; x >= 0; x--) { ... }
    • for (int x = 3; x > 10; x--) { ... }
    • for (int x = 3; x >= 0; x) { ... }
    • for (int x = 0; x < 5; x++) { ... }: 5
    • for (int x = 0; x < 6; x += 2) { ... }: 3
    • for (int x = 5; x >= 0; x--) { ... }: 6
    • for (int x = 3; x > 10; x--) { ... }: 0
    • for (int x = 3; x >= 0; x) { ... }: infinite
31. Write a method named isMultipleOfThree that will return true if a given int value is a multiple of 3, else false.

    public static boolean isMultipleOfThree(int input) {
      return input % 3 == 0;
    }
    

32. Consider the following code and test suite:

    public static int doSomethingStrange(int input) {          
      if (input == 7) {
        return input;
      } else if (input == 8 || input < 5) {
        return input + 1;
      } else if (input > 25 && input < 100) {
        return input + 2;
      } else {
        return input + 3;
      }
    }
    @Test
    public void test1() {
      assertEquals(doSomethingStrange(7), 7);
    }
    @Test
    public void test2() {
      assertEquals(doSomethingStrange(-1), 0);
    }
    @Test
    public void test3() {
      assertEquals(doSomethingStrange(50), 52);
    }
    

    The test suite above misses certain behaviors in the code. Add the minimum number of tests needed to cover all behaviors, with one assertEquals call per test.

    @Test
    public void test4() {
      assertEquals(doSomethingStrange(8), 9);
    }
    @Test
    public void test5() {
      assertEquals(doSomethingStrange(100), 103);
    }
    

33. What is wrong with the following code, if anything?

    public static int testMe(int x) {
      return x + 5;
    }
    @Test
    public void test1() {
      assertEquals(testMe(7), 12);
    }
    public void test2() {
      assertEquals(testMe(0), 5);
    }
    

    Second test is missing @Test annotation.