Midterm Review Questions (without Answers)

The midterm exam will be broken into two components:

• A lab-based portion, on Monday, April 9, 2018
• A written (lecture-based) portion, on Wednesday, April 11, 2018

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 two 8 1/2 x 11 inch sheets of paper containing handwritten notes, and you may write on both sides of the paper. If you so choose, you can bring in different sheets of paper for each portion of the exam (they are on separate days, and you can keep it). It is recommended to write down anything you feel like you need to memorize. Historically, some students will also write down selected solutions to prior labs.

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.

The exam will focus on topics that have been covered since the previous exam. However, since everything with programming builds on itself, you should also be familiar with the topics covered on the prior exam.

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");               
   }
   

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;
   }
   

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

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;
   }
   

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);
     }
   }
   

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

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

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

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]);
    }
    

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]);
    }
    

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);
    }
    

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++;
    }
    

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");
    }
    

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

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

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);
    }
    

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
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
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);
    }
    

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);
    }
    

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);
    }
    

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

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

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

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

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

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

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

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

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

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

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) { ... }
31. Write a method named isMultipleOfThree that will return true if a given int value is a multiple of 3, else false.
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.
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);
    }
    

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

    public class Foo {
      private int x;
      public Foo(int y) {
        int x = y;
      }
      public int getX() {
        return x;
      }
    }
    

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

    public class Class1 {
      private int x;
      public Class1(int y) {
        y = x;
      }
    }
    

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

    public class Baz {
      private int x;
      public Baz(int y) {
        x = y;
      }
      public static int getX() {
        return x;
      }
    }
    

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

    public class Blah {
      public static int x;
      public Blah(int y) {
        x = y;
      }
      public int getX() {
        return x;
      }
    }
    

38. What is wrong with the following code, if anything (assume classes Foo and Bar are defined in Foo.java and Bar.java, respectively)?

    public class Foo {
      public Foo() {}
      private int doSomething() {
        return 0;
      }
    }
    public class Bar {
      public static void main(String[] args) {
        Foo f = new Foo();
        f.doSomething();
      }
    }
    

39. What is the output of the main method of Class4 below?

    public class Class2 {
      public Class2() {}  
      public void m() {
        System.out.println("foo");
      }
    }
    
    public class Class3 {
      public Class3() {}  
      public void m() {
        System.out.println("bar");
      }
    }
    
    public class Class4 {
      public static void main(String[] args) {
        Class2 x = new Class2();
        Class3 y = new Class3();
    
        x.m();
        y.m();
      }
    }
    

40. What is the output of the main method of Class5 below?

    public class Class5 {
      private int x;
      public Class5(int y) {
        x = y;
      }
      public void foo(int x) {
        System.out.println(x);
      }
      public void bar(int y) {
        System.out.println(x);
      }
      public static void main(String[] args) {
        Class5 obj = new Class5(7);
        obj.foo(1);
        obj.bar(2);
      }
    }