Chapter 5 Array-Based Structures © 2006 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

Overview ● General-Purpose Array-Based Structures – 5.1 Getting around fixed length arrays – 5.2 Stack and Queue interfaces – 5.3 List interface and the ArrayList class – 5.4 List traversal

Shrinking and Stretching Arrays ● Array lengths are determined and fixed when allocated. ● Many times implementations require variable lengths of items.

Shrinking and Stretching Arrays ● A Deck holds a varying number of Cards, fewer as Cards are dealt.

Shrinking and Stretching Arrays ● A Card has two fields, rank and suit.

Shrinking and Stretching Arrays

● By specifying a size, we can limit the range of available elements. ● The Deck capacity remains unchanged at 52.

Shrinking and Stretching Arrays

● Getting the number of Cards in the Deck and testing for an empty Deck are trivial. i.e. get the size variable.

Shrinking and Stretching Arrays ● Only method to modify the size is the deal() method which removes and returns one Card from the Deck. ● size is decremented but the array still references the last element.

Shrinking and Stretching Arrays ● shuffle() should position the Cards randomly through the Deck. ● For each position in the Deck, randomly select another position in the Deck and swap Cards.

Shrinking and Stretching Arrays ● What if a structure needs to grow beyond its original capacity? ● Copy the entire contents of the array into a new, larger array.

Implementing Stacks and Queues ● ArrayStack Class – Similar to Deck class in that it contains an array data and an int size.

Implementing Stacks and Queues ● The isEmpty() method is identical to the one from Deck. ● The pop() method is similar to deal().

Implementing Stacks and Queues ● The peek() method is simpler than pop().

Implementing Stacks and Queues ● If the push() method is called when the data array is full, the array must be streched.

Implementing Stacks and Queues

● ArrayQueueClass – Adding something to an ArrayQueue is exactly like pushing it onto an ArrayStack. ● Removing an element must cause the front of the queue to move along the array.

Implementing Stacks and Queues ● When insertions runs up against the right end of the array, the queue must wrap around, so that the next element added goes at position 0. or

Implementing Stacks and Queues

The List Interface ● Stacks and queues limit access to the data to one end or the other. ● The List Interface has a more general-purpose use. ● A List is similar to an array, but it does not have a fixed size.

The List Interface

Input list.add("eggs"); list.add("bread"); list.add("tea"); list.contains("eggs"); list.contains("rutabagas"); list.get(1); list.isEmpty(); list.remove(0); list.remove("llamachow"); list.remove("tea"); list.size(); Return Value true false “bread” false true 1 List [ eggs ] [ eggs bread ] [ eggs bread tea ] [ bread tea ] [ bread ]

The List Interface ● The ArrayList's structure is similar to the ArrayStack and ArrayQueue.

The List Interface ● Some methods are trivial: – get(int index) – set(int index, E target) – add(E target) ● Some are identical to the ArrayStack methods: – isEmpty() – isFull() – size() – stretch()

The List Interface ● contains() method searches the list for an object.

The List Interface ● remove() removes and returns the item at a given location or removes the first occurrence of a particular item, if any.

The List Interface ● remove() shifts all subsequent elements one place to the left.

Iterators ● Often a List must be traversed. ● Because, outside of the class, access to the data is limited, an Iterator interface can be used to traverse the List.

Iterators

● Iterator general use: ● Warning: Each call to next() advances the Iterator.

Iterators ● java.util.NoSuchElementException – Thrown when the Iterator has reach it's end and next() is called. – Avoided by preceding all next() calls by a hasNext() test. ● java.util.IllegalStateException – Thrown when next() has never been invoked, or has not been invoked since the last invocation of remove().

Iterators ● The Iterable interface requires one method. ● When using Iterators, an enhanced for loop can be used.

Iterators

● The iterator() method for ArrayList creates an instance of ArrayIterator. ● The ArrayIterator references the ArrayList. ● An int is also used to indicate how far down the ArrayList we've traveled. ● A previous index is useful to the remove() method.

Iterators

● Keep going until the sum of the players’ scores is 13. ● A player keeps playing until he must “Go Fish”.

Iterators

● The computerTurn() method is similar to playerTurn() method but the rank is chosen randomly. ● Rather than repeat work to covert a number to a rank, a Card of the rank in question is created from the number. The suit doesn't matter (HEARTS is arbitrarily specified).

Iterators

● Both of the methods in the GoFishHand class involve Iterators, so we import java.util.Iterator. ● give() transfers all Cards of a given rank from one hand to another and returns a boolean indicating if any were transferred. ● meldSets() removes all sets of 4 same-rank Cards and returns the total number of sets.

Iterators

Java Collections Framework

● The java ArrayList is similar to the one implemented in this chapter. ● The Vector class is still present for backward compatibility. New code should use the ArrayList class. ● The framework does not include a Stack interface, but it does include a Stack class that extends the Vector class. ● There is a Queue interface, but no array-based implementation.

Java Collections Framework ● List is implemented by the class AbstractList. ● Abstract class instances can only be created by instantiating non-abstract classes that extend it. ● An abstract class is similar to an interface in that is defines abstract methods. ● The difference is that abstract classes may contain fields and non-abstract methods.

Java Collections Framework

Summary ● Array sizes cannot be changed, but the array- based structures can maintain varying sizes of data. ● Lists such as ArrayList provide basic methods for accessing elements and return Iterators. ● An Iterator allows us to traverse the List, visiting each element. ● Java’s collections framework includes a List interface, an ArrayList class, a Stack class, and a Queue interface.