EECS1030M Test 2

Wednesday January 28, 2015, 16:00-17:30
Lab 01
Version E

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

/**
 * This utility class contains some methods for lists of integers.
 * 
 * 
 * @author Franck van Breugel
 */
public class Test2E 
{
    private Test2E() {}

    /**
     * Returns an empty list of integers.
     * 
     * @return an empty list of integers.
     */
    public static List empty()
    {
	return new ArrayList();
    }
    
    /**
     * Returns the list containing the given number.
     * 
     * @param number an integer.
     * @return the list containing the given number.
     * @throws IllegalArgumentException if number <= 0
     */
    public static List single(int number) throws IllegalArgumentException
    {
	if (number <= 0)
	{
	    throw new IllegalArgumentException();
	}
	else
	{
	    List single = new ArrayList();
	    single.add(number);
	    return single;
	}
    }
    
    /**
     * Returns the list consisting of the integer 1, 2, ..., number.
     * 
     * @param number an integer.
     * @pre. number > 0
     * @return the list consisting of the integer 1, 2, ..., number.
     */
    public static List interval(int number)
    {
	List interval = new ArrayList();
	for (int n = 1; n <= number; n++)
	{
	    interval.add(n);
	}
	return interval;
    }
    
    /**
     * Given a string of digits, each pair of digits
     * represents an interval.  For example, the string

     * 14217944

     * represents the intervals

     * [1, 2, 3, 4], [], [7, 8, 9], [4]

     * Note that the second interval is empty since 2 > 1.  Combine
     * all these intervals and return the resulting sorted list.  For 
     * the above example, this gives us

     * [1, 2, 3, 4, 7, 8, 9]

     * For the string

     * 1446

     * the list [1, 2, 3, 4, 5, 6] is returned.  Note that the list
     * does not contain duplicates.
     * 
     * @param sequence a string of digits.
     * @pre. sequence != null && sequence.length() > 0 && sequence.length is even && sequence only contains digits
     * @return the union of the intervals specified by the given sequence.
     */
    public static List union(String sequence)
    {
	Set set = new TreeSet();
	for (int i = 0; i < sequence.length(); i = i + 2)
	{
	    int first = sequence.charAt(i) - '0';
	    int second = sequence.charAt(i + 1) - '0';
	    for (int j = first; j <= second; j++)
	    {
		set.add(j);
	    }
	}

	List list = new ArrayList(set);
	return list;
    }
}

Other questions

Question 1

The value of the implicit parameter this of a non-static method is the object (reference) on which the method is invoked



Question 2

John argues that non-static attributes are declared to be private, because they do not show up in the API and therefore do not complicate the API. Tracy argues that non-static attributes are declared to be private, so that implementers can easily change their representation. Who is right?
A. John but not Tracy.
B. Tracy but not John.
C. Both.
D. Neither.



Question 3

The class MyInteger has a single attribute named value of type int. Consider the following implementation of the setValue method. 

/**
 * Sets the value.
 *
 * @param value the new value.
 * @pre. value >= 0
 */
public void setValue(int value)
{
   if (value >= 0)
   {
      this.value = value;
   }
}
Suggest one thing about the code that can be improved. You should not modify the javadoc, only the code. Explain why it is an improvement.

public void setValue(int value)
{
   this.value = value;
}
The precondition is the concern of the client, not the implementer.