The ArrayList Class

• Provides an array-based list that "shrinks" and "grows"
• Part of the java.util package (Collections API)
• Constructors:

  • ArrayList()    //List has an initial capacity of ten.

  • ArrayList(int initialCapacity)

• Methods (see Java API for more methods):
  • void clear() - removes all elements from the list
  • int size() - returns the number of elements in the list
  • boolean add(Object x) - appends x to end of list, returns true
  • Object get(int index) - returns the element at the specified index
  • Object set(int index, Object x) - replaces the element at index with x returns the element formerly at index position
  • void add(int index, Object x) - inserts x at index position, sliding elements at index and higher to the right and adjusts size
  • Object remove(int index) - removes element at index, sliding elements at index + 1 and higher to the left and adjusts size, returns element formerly at index

What kind of element can be stored in an ArrayList?

To store a primitive data type in an ArrayList we must "wrap" it in an Object by using one of the 8 "type-wrapper" classes:

1. Integer
2. Double
3. Byte
4. Short
5. Float
6. Long
7. Character
8. Boolean

Sample Program
import java.util.*;

public class TestArrayList {

  public static void main(String args[]) {
  
  
   ArrayList list = new ArrayList();

   list.add(new Integer(45));
   list.add(new Double(23.5));
   list.add(new Boolean(true));
   list.add(new Character('A'));

   for (int i = 0; i < list.size(); i++)
   
     System.out.println(list.get(i));
     
  }
}

/* Output:
csc% java TestArrayList
45
23.5
true
A
*/