Array Lists

1
Array Lists

• pg. 234-239

2
Arrays in C

• Can set size at run time (as in C)
• int actualSize
• Emp staff new Emp actualSize
• Does not completely resolve problem of
  dynamically modifying arrays once array size is
  set, cannot change easily.

3
ArrayList class in C

• Untyped collections defined in System.Collections
  package
• Typed collections in System.Collections.Generic
  package
• Shrink and grow dynamically
• Lower bound is 0
• Holds references to objects
• Need to cast whenever you take an item out of an
  typed array list

4
add Method

• ArrayList staff new ArrayList( )
• staff.add (new Emp ( ) )
• staff.add (new Emp () )
• ArrayList class manages internal array of object
  references.
• When it gets full, then the array list
  automatically creates a bigger array and copies
  objects in smaller array to bigger array.

5
Size stuff

• Returns actual number of elements in array list
• staff.Count
• When you know it has reached permanent size
• staff.TrimToSize ( )

6
Accessing Array List elements

• To get ith element (object), staff i
• To get ith element (if typed) , must cast
• employee e (Emp) staff i

7
ArrayList Trick

• Flexible growth and convenient element access
• First make an array list and add elements
• ArrayList list new ArrayList ( )
• while ( )
• x
• list.add (x)
• Then use ToArray method to copy elements into
  array.

8
ArrayList Trick

• Then use ToArray method to copy elements into
  array (untyped)
•   int a  (int) list.ToArray(typeof(int)) 
• Other convenient methods
• Contains (object)
• BinarySearch (object)
• Sort( )