ArrayLists

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An ArrayList object has several important characteristics:

• You can access any item in the list as easily as any other item, if you know the item's index (location) in the list. You can also access any item equally quickly as any other item, whether it is the first item, the 10th item, or the last item. This is called random access.
• You can add or delete an item to or from the end of the list quickly and easily.
• You can add or delete an item to the beginning or middle of the list, but this is slower because it requires shifting all of the items after it in the list.
• Technically, an ArrayList can contain only class objects, not primitive types. Fortunately, there are wrapper types, e.g., Integer, Float, Double, and Boolean. If you construct an ArrayList of one of these then you can put values of the associated primitive type in the list. The compiler will automatically wrap the primitive type up as an obect of its associated wrapper class (known as auto-boxing. When you retrieve the object (using the get method, for example), the compiler will automatically unwrap the primitive from its wrapper (known as auto-unboxing). For example:

          ArrayList<Integer> numberList = new ArrayList<Integer>();
          numberList.add(42);
          int listItem = numberList.get(0); 

A subset of handy ArrayList methods:

size()		returns number of elements in list
isEmpty()		returns true if the list is empty; false otherwise
add(E element)		adds given element to end of list
add(int index, E element)		adds given element at specified index list, shifting later elements
get(int index)		returns element at specified index
set(int index, E element)		replaces the element currently at the specified index with the given element
remove(E element)		finds given element in list and removes it (first occurrence)
remove(int index)		removes element at specified index list, shifting later elements