EECS2030 Sample Test 2

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Set;

/**
 * A utility class for Test 2.
 * 
 * @author EECS2030
 * 
 */
public class Test2C {

	private Test2C() {}
	
	/**
	 * Returns the character at the beginning of the string s.
	 * 
	 * @param s
	 *            a string
	 * @pre. s.length() > 0
	 * @return the character at the beginning of s
	 */
	public static char first(String s) {
		return s.charAt(0);
	}

	/**
	 * Returns the second character of the string s.
	 * 
	 * @param s
	 *            a string
	 * @return the second character of s
	 * @throws IllegalArgumentException
	 *             if the length of the string is less than 2
	 */
	public static char second(String s) {
		if (s.length() < 2) {
			throw new IllegalArgumentException("string must have length of 2");
		}
		return s.charAt(1);
	}

	/**
	 * Returns the longest string contained in the set t. If the set t is empty
	 * then the empty string is returned.
	 * 
	 * @param t
	 *            a set of strings
	 * @return the longest string contained in t, or the empty string if t is
	 *         empty
	 */
	public static String longest(Set<String> t) {
		String result = "";
		int len = 0;
		for (String s : t) {
			if (s.length() > len) {
				len = s.length();
				result = s;
			}
		}
		return result;
	}

	/**
	 * Searches a list of strings for the string that occurs the most
	 * frequently. For example, if list t is:
	 * 
	 * <p>
	 * ["a", "b", "b", "c"]
	 * 
	 * <p>
	 * then the string "b" is returned.
	 * 
	 * <p>
	 * If more than one string occurs with the greatest frequency then the
	 * string that comes first in dictionary order is returned. For example, if
	 * list t is:
	 * 
	 * <p>
	 * ["zed", "pop", "pop", "are", "are"]
	 * 
	 * <p>
	 * then the string "are" is returned.
	 * 
	 * @param t
	 *            a list to search
	 * @pre. t contains at least one string
	 * @return the string that occurs most frequently in the list
	 */
	public static String mostFrequent(List<String> t) {
		List<String> sorted = new ArrayList<String>(t);
		Collections.sort(sorted);
		String mostFreq = sorted.get(0);
		int max = 1;
		String s = sorted.get(0);
		int count = 1;
		for (int i = 1; i < sorted.size(); i++) {
			String next = sorted.get(i);
			if (s.equals(next)) {
				count++;
				if (count > max) {
					max = count;
					mostFreq = s;
				}
			} else {
				s = next;
				count = 1;
			}
		}
		return mostFreq;
	}

}

Multiple choice question

Complex y = new Complex(1, 5);
Complex z = new Complex(1, 5);
y.setReal(-3);

        100 |     client      |
     y      |  400a           |
     z      |  500a           |
            |                 |
            |                 |
        400 | Complex object  |
  real      |  1              |
  imag      |  5              |
            |                 |
            |                 |
        500 | Complex object  |
  real      |  1              |
  imag      |  5              |
            |                 |
            |                 |
        800 | Complex setReal |
  this      |                 |
  real      |  -3             |
            |                 |

public class Student {
  private String studentNumber;
  
  // constructor not shown, but guaranteed to be correct

  @Override
  public boolean equals(Object obj) {
    if (this == obj) {
      return true;
    }
    if (this.getClass() != obj.getClass()) {
      return false;
    }
    Student other = (Student) obj;
    return this.studentNumber == other.studentNumber;
  }
  
  // hashCode not shown, but guaranteed to be correct
}