EECS2030Z Test 2

State the definition of a method precondition.

A method precondition is a condition that the client must ensure is true immediately before a method is invoked.

Grading scheme: 3 marks total.

Suppose that the method name zipper from Question 1 was implemented like so:

public static List<Integer>(List<Integer> s, List<Integer> t) {
  List<Integer> result = new ArrayList<Integer>();
  /* code not shown here that assigns the correct value to result */
  return result;
}

Suppose a client writes a main method that includes the following two lines of Java code:

List<Integer> s = Arrays.asList(5, 7);    // the list [5, 7]
List<Integer> t = Arrays.asList(6, 8);    // the list [6, 8]
List<Integer> z = Utility2D.zipper(s, t);

The memory diagram illustrating the state of memory for the three lines of client code is shown below. What suitable values of a, b, and c would complete the memory diagram?

           ---------------------
           |    main method    |
           ---------------------
   s    100|       300a        |
   t    102|       400a        |
   z    104|        a?         |
           ---------------------
           |                   |
           |                   |
           ---------------------
        300|    List object    |
           ---------------------
           |                   |
           |                   |
           ---------------------
        400|    List object    |
           ---------------------
           |                   |
           |                   |
           ---------------------
           |     distance      |
           ---------------------
     s  500|        b?         |
     t  502|    (not shown)    |
result  504|        c?         |
           ---------------------
           |                   |
           |                   |
           ---------------------
        600|    List object    |
           ---------------------
           |                   |

a = 600a, b = 300a, c = 600a

a and c are both equal to the address of the returned list. b is equal to the address of the first list passed to the method.

Grading scheme: 3 marks total (1 for each of a, b, and c).

Provide the Javadoc necessary to exactly reproduce the API documentation for the constructor Rotation(double angle, String units) from Question 2.

	/**
	 * Initializes the rotation to the given angle using the given
	 * units.
	 * 
	 * @param angle the angle of the rotation
	 * @param units the units of the angle
	 * @throws IllegalArgumentException if units is not equal
	 * to Rotation.DEGREES or Rotation.RADIANS
 	 */

Provide 3 test cases for the method Utility2D.interval. Make sure that each test case tests a different feature of the method; try to include one boundary test case. For each test case, provide a one sentence explanation of what the test case is testing.

There are many possible test cases; below are 3 examples:

a                    : 1
b                    : 1
expected return value: [1]
explanation          : boundary case where a == b      

a                    : 1
b                    : 5
expected return value: [1, 2, 3, 4, 5]
explanation          : tests a typical case where a < b

a                    : 5
b                    : 1
expected return value: [1, 2, 3, 4, 5]
explanation          : tests a typical case where b < a

Consider the following class and its implementation of equals(Object):

public class Bool {

  private boolean value;
  private String name;

  @Override
  public boolean equals(Object obj) {
    if (this == obj) {
      return true;
    }
    if (obj == null) {
      return false;
    }
    if (this.getClass() != obj.getClass()) {
      return false;
    }
    Bool other = (Bool) obj;
    if (this.name != other.name) {
      return false;
    }
    if (this.value && other.value == false) {
      return false;
    }
    return true;
  }

}

Explain whether or not the implementation shown above satisfies the equals contract. Does it contain any errors not related to the equals contract?

The implementation does not satisfy the equals contract because x.equals(x) == true is not always true! This occurs when this.value == false because x.equals(x) returns in the following if statement:

    if (this.value && other.value == false) {
      return false;
    }

Grading scheme: 4 marks total.

2 marks for stating x.equals(x) == true is not always true. 2 marks for the explanation.