CS18000: Programming I

Transcription

1 CS18000: Programming I Dynamic Data Structures 12 April 2010 Prof. Chris Clifton More on Dynamic Data Structures Difficulties with Dynamic Data Structures: Removing self Solution 1: Violate Encapsulation Operate on your child Move child to self LinkedSet s = item5 item1 item2 item3 item4 4/15/2010 CS Chris Clifton 1

2 Dynamic Data Structure: Search Tree Showed binary search tree in the past Didn t deal with delete def Now: Delete by breaking encapsulation chr abc xyz 4/15/2010 CS Exceptions as a Programming Technique Difficulties with Dynamic Data Structures: Removing self Pointers to head of structure Solution 1: Violate Encapsulation Operate on your child Move child to self Solution 2: Exceptions LinkedSet s = item5 item1 item2 item3 item4 4/15/2010 CS Chris Clifton 2

3 Idea: Inform Parent Tell parent to eliminate us Parent has called us with recursive call Return new head void remove(item); Should it be LinkedSet<E> remove(e item);? Does this make sense if nothing changed? What if we want to return (for example) the removed item? Solution: throw exception Exception has information parent needs to know 4/15/2010 CS Exception that Carries Information class NewHead extends Exception { LinkedList<E> head; NewHead ( LinkedList<E> head ) { E removeditem = null; NewHead ( LinkedList<E> head, E item ) { removeditem = item; 4/15/2010 CS Chris Clifton 3

4 public class LinkedList<E> { private E current; private LinkedList<E> next = null; public class NewHead extends Exception { private LinkedList<E> head; public NewHead(LinkedList<E> head) { public LinkedList<E> newhead() { return head; public LinkedList ( E item ) { current = item; private LinkedList (E item, LinkedList<E> next) { current = item; this.next = next; public E getitem() { return current; public void addafter(e item) { next = new LinkedList<E>(item, next); 4/15/2010 CS public class LinkedList<E> { private E current; private LinkedList<E> next = null; public class NewHead extends Exception { private LinkedList<E> head; public NewHead(LinkedList<E> head) { public LinkedList<E> newhead() { return head; public void append( E item ) { if ( next == null ) addafter(item); else next.append(item); public void addbefore(e item) throws NewHead { LinkedList<E> newlist = new LinkedList<E>(item, this); throw new NewHead(newList); public boolean contains(e item) { if ( item.equals(current) ) return true; else if (next == null) return false; else return next.contains(item); 4/15/2010 CS Chris Clifton 4

5 public class LinkedList<E> { private E current; private LinkedList<E> next = null; public class NewHead extends Exception { private LinkedList<E> head; public NewHead(LinkedList<E> head) { public LinkedList<E> newhead() { return head; public void remove(e item) throws NewHead { if (item.equals(current)) // Eliminate ourself throw new NewHead(next); else if ( next!= null ) { try { next.remove(item); catch (NewHead e) { next = e.newhead(); 4/15/2010 CS CS18000: Programming I Dynamic Data Structures: 14 April 2010 Prof. Chris Clifton 2010 Chris Clifton 5

6 Full encapsulation All operations on self Only point to child Exceptions to notify of changes Pass data in exception Hide all internals from outside world Private nested classes LinkedList s = item5 item1 item2 item3 item4 4/15/2010 CS Problem: Changing Head a Bad Idea! UseList works But what if s given to someone else My s changes, theirs doesn t Solution: Separate root from elements public class LinkedList<E> { private class LinkedListElem<E> { LinkedListElem<E> head; addbefore( item E ) { try { head.addbefore( item ); catch ( NewHead e ) { head = e.gethead(); Linked list s= t=s; item5 item1 item2 item3 item4 4/15/2010 CS Chris Clifton 6

7 public class LinkedList<E> implements java.util.iterator<e> { private LinkedListElem<E> first= null; private LinkedListElem<E> currentiterator = null; private class NewHead extends Exception { private LinkedList<E> head; public NewHead(LinkedListElem<E> head) { public LinkedListElem<E> newlist() { return head; public void prepend(e item) { if (first == null) { first = new LinkedListElem<E>(item); currentiterator = first; else { try { first.addbefore(item); catch ( LinkedList.NewHead e ) { first = e.newlist(); public void append(e item) { if (first == null) { first = new LinkedListElem<E>(item); currentiterator = first; else first.append(item); 4/15/2010 CS // Iterator operations. public boolean hasnext() { return currentiterator!= null; public E next() throws java.util.nosuchelementexception { if (! hasnext()) throw new java.util.nosuchelementexception(); E result = currentiterator.getitem(); currentiterator = currentiterator.getnext(); return result; public void resetiterator() { currentiterator = first; : Iterator Operations public void insert(e item) { // Add item before iterator if (! hasnext()) throw new java.util.nosuchelementexception(); else { try { currentiterator.addbefore(item); catch ( LinkedList.NewHead e ) { if ( first == currentiterator ) first = e.newlist(); public void add(e item) { // Add item after iterator if (! hasnext()) throw new java.util.nosuchelementexception(); else currentiterator.addafter(item); 4/15/2010 CS Chris Clifton 7

8 public void remove(e item) { if (first!= null) { try { first.remove(item); catch ( LinkedList.NewHead e ) { first = e.newlist(); resetiterator(); // Might have been removed. public void remove() { // Removal at current iterator not implemented. public boolean contains(e item) { return ( first!= null && first.contains(item) ); 4/15/2010 CS Implemented as Elements: Private Class Public class exports operations Private class inside public class provides needed operations Hides head of list changes. public class LinkedList<E> implements java.util.iterator<e> { private class LinkedListElem<E> { // See LinkedList<E> from previous day s lecture. 4/15/2010 CS Chris Clifton 8