Arraylists: Collections Framework

ArrayLists: Collections Framework

Collections Framework unlike fixed-length arrays provides for the ability to produce variable length lists. There are a set of 7 different types of containers in the Collections Framework (List, Set, Map, Collections, Iterator, Comparator, Comparable). These containers cannot store primitives (use wrapper classes Integer, Double, etc. to create Objects).

List & Collection synonyms for a container.

Picture on page 432

Collections classis a helper class that supports the container

class. Allows you to search, sort, fill shuffle,

replace, reverse

Iterator class: Determines if more elements exist and returns the next element.

Comparator class: Used for sorting elements in a list

(default order)

Comparable class: Orders element to a supplied ordering

Sequence (used for sorting)

ArrayList

An ArrayLists expand and contract as needed.

ArarryList Structure picture p433

p436 Chart of ArrayList Class Methods

Other great ArrayList notes from Lawrenceville Press:

The Object class you are storing in the ArrayList must have an overridden equals() method.

How the ArrayList is sized used Capacity

Capacity is initially 10 and increase by 50% each time using

New Capacity = (3* Old Capacity)/2 + 1

Wrapper Classes Example

ArrayList<Integer> numlist = new ArrayList<Integer>();

numlist.add(0,new Integer(28)); ///called boxing

int n=numlist.get(0).intValue(); ///called unboxing

System.out.println();

Autoboxing implicitly converts primitive type data to reference

type.

ArrayList<Integer> numlist = new ArrayList<Integer>();

numlist.add(28);

int n=numlist.get(0);

System.out.println();

Collections Helper Classes

Summary of Commonly Used Collections Class Methods:

• int binarySearch(List list,Object obj)
• void copy(List list1,List list2)
• void fill(List list, Object obj)
• Object max(Collection list) //returns max element using natural ordering
• Object min(Collection list) //returns min element using natural ordering
• void reverse(List list)
• void shuffle(List list)
• void sort(List list)

Refer to page 438 for Table 8.3

Example on page 439

Iterator Class

Keeps track of an object’s position within a container.

Iterator Methods:

• boolean hasNext() //returns true if the container has more elements
• element next() //returns the next element and advances the iterator
• void remove() //removes the element from the current iterator position

Iterator Example Code

int sum=0,intvalue;

ArrayList<Integer> x = new ArrayList<Integer>();

x.add(1);

x.add(2);

x.add(3);

x.add(4);

Iterator iter = x.iterator();

while (iter.hasNext())

{

intvalue= (Integer) iter.next();

sum=sum+intvalue;

}

Assignment:Create an Inventory Control System. You need to create a class that has the data members (product number, product description, product quantity and product price). Provide all the necessary constructors, accessors, modifiers and any other methods that you feel you need. Please allow the user to add, remove, update and list inventory records using an ArrayList. Note product number should be unique.