Andhra University 2007 B.E Computer Science s - Question Paper

int month; // Month number in range one to 12.
int day; // Day number in range one to 31.
int year; // Year number.
Date(int m, int d, int y) { // Convenience constructor.
month = m;
day = d;
year = y;
}
public int compareTo( Date otherDate ) {
// Returns 1, 0, or -1 if this date is greater than, equal to,
// or less than otherDate, respectively.
if (year < otherDate.year)
return -1;
else if (year > otherDate.year)
return 1;
else { // Years are equal; compare months.
if (month < otherDate.month)
return -1;
else if (month > otherDate.month)
return 1;
else { // Years and months are equal; compare days.
if (day < otherDate.day)
return -1;
else if (day > otherDate.day)
return 1;
else
return 0;
}
}
}
}

ques. 10:

Suppose that syllabus is a variable of kind TreeMap, where Date is the class from the preceding exercise. Write a code segment that will write out the value string for every key that is in the month of December, 2006.
Answer:

I will provide 2 solutions. 1 of them simply looks up every date in December, 2006 in the map and prints the corresponding value, if there is one. The other iterates though a submap that contains all the entries for dates in that month.

A solution using the map's get() method:

for (int day = 1; day <= 31; day++) {
// Get the info for 1 day in December, 2006
Date date = new Date(12,day,2006); // The key.
String info = syllabus.get(date); // Get the value for that key.
// (Can be null if there is no
// entry in the map for this date.)
if (info != null)
System.out.println("December " + day + ": " + info);
}


A solution using a submap (harder, but more efficient):

Date startDate = new Date(12,1,2006); // Starting date for submap.
Date endDate = new Date(1,1,2007); // Ending date for submap.
// (Remember that the end date
// is not included.)
Map decemberData = syllabus.subMap(startDate, endDate);
for ( Map.Entry entry : decemberData ) {
Date date = entry.getKey();
String info = entry.getValue();
System.out.println("December " + data.day + ": " + info);
}

ques. 11:

Write a generic class Stack that can be used to represent stacks of objects of kind T. The class should include methods push(), pop(), and isEmpty(). Inside the class, use an ArrayList to hold the items on the stack.
Answer:

public class Stack {
ArrayList stack = new ArrayList();
public void push( T newItem ) {
stack.add(newItem);
}
public T pop() {
int top = stack.size() - 1; // location of top item
return stack.remove(top); // remove and return top item
}
public boolean isEmpty() {
return stack.size() == 0;
}
}

ques. 12:

Write a generic method, using a generic kind parameter , that replaces every occurrence in a ArrayList of a specified item with a specified replacement item. The list and the 2 items are parameters to the method. Both items are of kind T. Take into account the fact that the item that is being changed might be null. For a non-null item, use equals() to do the comparison.
Answer:

Since the method operates on ArrayLists, it can use indexed access with the get(i) and set(i,item) methods. These operations are efficient for array lists. I also provide a 2nd version of the method that uses a list iterator and is efficient for any kind of list.

public static void replaceAll(ArrayList list, T oldItem, T newItem) {
if (oldItem == null) {
for (int i = 0; i < list.size(); i++) {
if ( null == list.get(i) )
list.set( i, newItem );
}
}
else {
for (int i = 0; i < list.size(); i++) {
if ( oldItem.equals(list.get(i)) )
list.set( i, newItem );
}
}
}


public static void replaceAll(List list, T oldItem, T newItem) {
ListIterator iter = list.listIterator();
while (iter.hasNext()) {
T listItem = iter.next();
if ( oldItem == null ) {
if ( listItem == null )
iter.set(oldItem);
}
else {
if ( oldItem.equals(listItem) )
iter.set(oldItem);
}
}
}

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