Generics and the ArrayList Class - Java - page 705

Suppose list starts out empty and your code executes our four add invocations,
which we repeat below:
list.add("One");
list.add("Two");
list.add("Three");
list.add(0, "Zero");
After these four invocations of add , list would contain the strings "Zero" , "One" ,
"Two" , and "Three" in positions 0 , 1 , 2 , and 3, respectively.
Note that the two-argument version of add cannot add an element at just any
position. It can only insert an element at some already used position or at the first
unused position. The elements in an ArrayList always occupy a contiguous set of
positions starting at 0 ; that is, they are always at positions 0 , 1 , 2 , and so forth up to
some last position. This is just like a partially filled array (as discussed in Chapter 6),
but unlike a partially filled array, you do not need to do anything to keep track of
how many elements are on the list. The method size automatically takes care of this
for any ArrayList .
The add Methods
Elements can be added to an ArrayList by using the methods named add . The elements
are added to index position 0 , then 1 , then 2 , and so forth so there are no gaps in the indices
of elements.
The most straightforward method to use for adding to an ArrayList is the method named
add that has only one parameter.
EXAMPLES
list.add("Salud");
list.add("Dinero");
list.add("Java");
The object list is an ArrayList with base type String .
A second method named add allows you to add an element at any currently used index posi-
tion or at the first unused position. When inserting into an ArrayList with this version of
add , elements at the specified index and higher (if any) are moved up one position to make
room for the new element.
list.add(1, "Amor");
If list starts out empty and all four statements in the two sets of examples are exe-
cuted, then list would contain the following strings in the order given: "Salud" , "Amor" ,
"Dinero" , and "Java" .