API Contents - SCJP Sun Certified Programmer for Java Platform SE6 - page 320

FIGURE 4.11 A regular expression that contains character classes

Next must come
1 on more white
space characters

The sequence must
end with 1 or more
word characters.

[A-Z] \\w * \\s [A-Z] \\w

The sequence must
start with a single
uppercase letter
between A and Z

Next can come
any number
(including 0) of
word characters

Next must come
an uppercase
letter between
A and Z

The string “JohnDoe” is not a match because it does not contain any whitespace charac-
ters. “John doe” is not a match because the second word does not start with a letter from
A to Z . “J D” is not a match because the D is not followed by one or more word characters.
The other strings in the names array match, so the output of the code is

John Doe matches [A-Z]\w*\s+[A-Z]\w+
John Doe matches [A-Z]\w*\s+[A-Z]\w+
J D5 matches [A-Z]\w*\s+[A-Z]\w+

As you can see, regular expressions can become quite complex, but their complexity
makes them a powerful tool for matching character sequences. They also show up in other
Java API classes and methods, including the String.split method, which we discuss next.

The String.split Method

The String class contains a method named split that takes in a regular expression and
splits the String object into an array of String objects. The signature of the split method
is public String [] split(String regex) .
The String argument is a regular expression, and the return value is one or more String
objects in an array. The size of the array depends on how many matches of the regular
expression are found. For example, the following statements split a String object into three
String objects:

String greetings = “hi;hello;welcome”;
String [] greetingsArray = greetings.split(“;”);
for(String greeting : greetingsArray) {
System.out.println(greeting);
}

The regular expression in the call to split is the string literal “;” that appears twice in
the greetings String . The greetingsArray contains three elements. The output of the
code is