API Contents - SCJP Sun Certified Programmer for Java Platform SE6 - page 315

The parse method throws a ParseException if the beginning of the string
cannot be parsed. As with the parse method in NumberFormat , the parse
method in DateFormat successfully parses a string if the beginning of the
string is in the proper format.
The DateFormat class is useful when you develop Java applications that need to
work with formatted dates and times. The next section discusses some useful classes
for working with regular expressions.
Regular Expressions
A regular expression is a sequence of characters that describes a pattern of characters.
The pattern describes a set of strings based on common characteristics. The syntax for a
regular expression is not unique to Java, and they are used in many different programming
languages. Java uses the Pattern and Matcher classes in the java.util.regex package for
using regular expressions in your Java applications.
For the exam you should be able to write code that uses the Pattern and Matcher classes
and the String.split method. You also need to be able to “recognize and use regular
expression patterns for matching (limited to: . (dot), * (star), + (plus), ? , \d , \s , \w , [] , () ).”
The objectives specifi cally state that what you need to know about “the use of * , + , and ?
will be limited to greedy quantifi ers, and the parentheses operator will only be used as a
grouping mechanism, not for capturing content during matching.” This section discusses
these topics in detail, starting with a discussion on the Pattern and Matcher classes.
The Pattern and Matcher Classes
The Pattern class represents a compiled regular expression. You do not instantiate a Pat-
tern object; instances are obtained from the static compile method defi ned in the Pattern
class public static Pattern compile(String regex) .
Regular expressions need to be compiled into a pattern. The resulting Pattern object is
used to obtain a Matcher instance. A Matcher object represents the engine that performs
the actual parsing on the character sequence to see if it matches the pattern.
The following statements represent a typical usage of the Pattern and Matcher classes:
5. String regex = “hello”;
6. Pattern pattern = Pattern.compile(regex);
7. Matcher m1 = pattern.matcher(“hello”);
8. Matcher m2 = pattern.matcher(“goodbye”);
9. if(m1.matches()) {
10. System.out.println(“hello is a match”);