ArrayLists

ArrayLists

1. Resizable-array implementation of the List interface.

   • is an abstraction from programmer manipuplation of Arrays
   • part of Collections API

2. Implements all optional List operations

3. elements can be any object type and null

   • uses generics<T>

4. create new ArrayList object

   • ArrayList<String> list = new ArrayList<String>()
   • deafault size at creation is 10. can specify required size as constructor parameter
   • specify class name of objects it will hold in <>. can use empty <> after new.
   • Array is used as underlying hidden data structure

5. size increases automatically if add to full arraylist

6. METHODS

   • size: number of indices with elements
     • int x = list.size()
   • remove element
     • remove & return element at index i : E elem=list.remove(i);
     • remove 1st match of element e: boolean b = list.remove(e);
     • remove all elements: list.clear();
   • add element
     • add element at end: list.add("something")
     • insert at position of index: list.add(i, elem)
   • replace element: list.set(index, "something else");
   • get element at index i: E e= list.get(i);
   • list.contains(e)
   • list.isEmpty();

7. for-each or enhanced for loop can be used

8. ArrayList vs Array

   • AL: less efficient; not have convenient[ i] use; base type must be a class, not primitive(can use wrappers);
   • A: can't change in size - AL grow/shrink during use; A: need to keep cnt of elements in it- AL: does this auto; A: have NO methods - AL: powerful methods for manipulation