COM S 228Collections and Iterators

Instructor: Ying Cai

Department of Computer ScienceIowa State Universityyingcai@iastate.eduOffice: Atanasoff 201

Java Collection Framework

• Very often we need a way to store and access a collection of elements of the same type

• A few factors to consider

Factors to Considers

Factors to Considers

Java Collections Framework

Key methods of Collection<E>

Key methods of Iterator<E>

Java Collections Framework

foreach loop

AbstractCollection<E>

An Array-Based Generic Collection

Basic data structure

Constructors

complexity of adding n items?

Iterators

Iterators

Array-based Implementation of FirstCollection

Data size: the index of next available slot

Iterator

Cursor: the index of the item retrieved by next()

checkCapacity()

• hasNext()• next()• remove()

Advantages•Simple to implementDisadvantages•A certain amount of memory is required for the array, even when the collection contains few elements•Removing an element requires all elements down to be shifted, making it an O(n) operations

Singly-Linked Lists

data next

We can build a list like this

Null-terminated singly-linked list

We can access any element by starting at head

Mostly, we will use a loop:

We can build a list like this

Null-terminated singly-linked list

Suppose we have this list

Now we do this

The result is

This effectively removes the node containing c

Suppose we have this list

What happens if we do this

Problems with Singly-Linked Lists

• Cannot quickly access the predecessor, making it difficult to delete an element

• Can only iterate in one direction

Doubly-Linked Lists

Iterator for Doubly-Linked Lists

cursor

cursor

FirstCollection

Iterator

Cursor: the index of the item retrieved by next()

• hasNext()• next()• remove()

Array data

Singly-Linked-List

Doubly-Linked-List

The List InterfaceA list is a linearly ordered collection with random access to the elements. The List interface extends the Collection interface:

List

Two ListIterator

Two ListIterator

We will implement the List interface on top of the Existing class AbstractSequentialList.

A Doubly-Linked List Implementation

Some helpful methods

current

newNode

A Doubly-Linked List Implementation

ListIterator

cursor

cursor

cursor

cursor

remove() needs to know whichdirection we’are coming from,AHEAD, BEHIND, or NONE. Afterit has been called, we have to setdirection to NONE, so that it doesnot get called unless there’sanother next() or previous().

Array-based Implementation of List A list is a linearly ordered collection with random access to the elements. The List interface extends the Collection interface:•Void add(int k, E item)•E get(int k)•E set(int pos, E element)•E remove (int k)•ListIterator() and ListIterator(int pos)

• next(), hasNext()• nextIndex(), previousIndex(), add(E item)

Array data

Doubly-Linked-List

Array or Doubly-Linked-List?

Array data

Doubly-Linked-List

Array data

Doubly-Linked-List

Array data

Doubly-Linked-List