Generics and the ArrayList Class - Absolute Java - page 766

The size Method
The method size returns the number of elements in an ArrayList .
EXAMPLE
for ( int index = 0; index < list.size(); index++)
System.out.println(list.get(index));

list is an ArrayList object.

TIP: Summary of Adding to an ArrayList

To place an element in an ArrayList position (at an ArrayList index) for the first
time, you usually use the method add . The simplest method named add has a single
parameter for the element to be added and adds elements at index positions 0 , 1 , 2 ,
and so forth, in that order.
You can add an element at an already occupied list position by using the two-parameter
version of add . When inserting into an ArrayList with this version of add , elements at
the specifi ed index and higher are moved up one position to make room for the new ele-
ment. For example, suppose list is an ArrayList object with base type String that has
three elements already on its list. Consider the following method invocation:
list.add(1, "Amor");
Before, there were elements at index positions 0, 1 , and 2 . When this invocation of
add is executed, the element "Amor" is inserted at index 1 , and the elements at index
positions 1 and 2 are moved to positions 2 and 3 .
You can also use the two-argument version of add to add an element at the fi rst
unused position. If list has elements at index positions 0, 1, 2 , and 3 , then the fol-
lowing is legal:
list.add(4, "Mucho Amor");
Your code can then go back and change any individual element, using set . However,
set can reset only the element at an index that already has an element.
The method size can be used to determine how many elements are stored in an
ArrayList .

add

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Self-Test Exercises

1. Suppose list is an object of the class ArrayList<String> . How do you add
the string "Hello" to the ArrayList list ?
2. Suppose instruction is an object of the class ArrayList<String> that contains
the string "Stop" at index position 5 . How do you change the string at index
position 5 to "Go" (without changing any of the elements at other positions)?
3. Suppose instruction is an object of the class ArrayList<String> that contains
strings at index positions 0 through 10 . How do you insert the string "Go" at index
position 5 so that no strings are removed from the list instruction ?