ArrayLists - Building Java Programs: A Back to Basics Approach - page 632

The indexOf method takes a particular value and returns the index of the first
occurrence of the value in the list. If it doesn't find the value, it returns -1 . So, you
could write a replace method as follows:
public static void replace(ArrayList<String> list,
String target, String replacement) {
int index = list.indexOf(target);
if (index >= 0) {
list.set(index, replacement);
}
}
Notice that the return type of this method is void , even though it changes the con-
tents of an ArrayList object. Some novices think that you have to return the
changed ArrayList , but the method doesn't actually create a new ArrayList ; it
merely changes the contents of the list. As you've seen with arrays and other objects,
a parameter is all you need to be able to change the current state of an object because
objects involve reference semantics in which the method is passed a reference to the
object.
You can test the method with the following code:
ArrayList<String> list = new ArrayList<String>();
list.add("to");
list.add("be");
list.add("or");
list.add("not");
list.add("to");
list.add("be");
System.out.println("initial list = " + list);
replace(list, "be", "beep");
System.out.println("final list = " + list);
This code produces the following output:
initial list = [to, be, or, not, to, be]
final list = [to, beep, or, not, to, be]
There is also a variation of indexOf known as lastIndexOf . As its name
implies, this method returns the index of the last occurrence of a value. There
are many situations where you might be more interested in the last occurrence
rather than the first occurrence. For example, if a bank finds a broken automated
teller machine, it might want to find out the name and account number of the last
customer to use that machine. Table 10.2 summarizes the ArrayList searching
methods.