ArrayLists - Building Java Programs: A Back to Basics Approach - page 628

Java will make sure that you add values of an appropriate type. In this case,
because you requested an ArrayList<String> , you can add String s to the list.
When you ask an ArrayList to add a new value to the list, it appends the new value
to the end of the list.
Unlike with simple arrays, printing an ArrayList is straightforward because the
ArrayList class overrides Java's toString method. The ArrayList version of
toString constructs a String that includes the contents of the list inside square
brackets, with the values separated by commas. Remember that the toString
method is called when you print an object or concatenate an object to a String . As a
result, you can print ArrayList s with a simple println :
System.out.println("list = " + list);
For example, you can add println statements as you add values to the list:
ArrayList<String> list = new ArrayList<String>();
System.out.println("list = " + list);
list.add("Tool");
System.out.println("list = " + list);
list.add("Phish");
System.out.println("list = " + list);
list.add("Pink Floyd");
System.out.println("list = " + list);
Executing this code produces the following output:
list = []
list = [Tool]
list = [Tool, Phish]
list = [Tool, Phish, Pink Floyd]
Notice that you can print the ArrayList even when it is empty and each time that
new values are added to the end of the list. The ArrayList class also provides an
overloaded version of the add method for adding a value at a particular index in the
list. It preserves the order of the other list elements, shifting values to the right to
make room for the new value. This version of add takes two parameters: an index
and a value to insert. ArrayList s use zero-based indexing, just as arrays and
String s do. For example, given the preceding list, consider the effect of inserting a
value at index 1:
System.out.println("before list = " + list);
list.add(1, "U2");
System.out.println("after list = " + list);