A Collection of Useful Classes - Beginning Java - page 719

StringBuffer , and StringBuilder classes so you can pass a reference of any of these types to the meth-
od. The java.nio.CharBuffer class also implements CharSequence , so you can pass the contents of a
CharBuffer to the method, too. This means that if you use a CharBuffer to hold character data you have
read from a file, you can pass the data directly to the matcher() method to be searched.
An advantage of Java's implementation of regular expressions is that you can reuse a Pattern object to
create Matcher objects to search for the pattern in a variety of strings. To use the same pattern to search an-
other string, you just call the matcher() method for the Pattern object with the new string as the argument.
You then have a new Matcher object that you can use to search the new string.
You can also change the string that a Matcher object is to search by calling its reset() method with a
new string as the argument. For example:
matchHad.reset("Had I known, I would not have eaten the haddock.");
This replaces the previous string, sentence , in the Matcher object, so it is now capable of searching
the new string. Like the matcher() method in the Pattern class, the parameter type for the reset()
method is CharSequence , so you can pass a reference of type String , StringBuffer , StringBuilder , or
CharBuffer to it.
Searching a String
Now that you have a Matcher object, you can use it to search the string. Calling the find() method for the
Matcher object searches the string for the next occurrence of the pattern. If it finds the pattern, the method
stores information about where it was found in the Matcher object and returns true . If it doesn't find the
pattern, it returns false . When the pattern has been found, calling the start() method for the Matcher
object returns the index position in the string where the first character in the pattern was found. Calling the
end() method returns the index position following the last character in the pattern. Both index values are
returned as type int . Therefore, you could search for the first occurrence of the pattern like this:
if(m.find()) {
System.out.println("Pattern found. Start: " + m.start() + " End: " + m.end());
} else {
System.out.println("Pattern not found.");
}
Note that you must not call start() or end() for the Matcher object before you have succeeded in find-
ing the pattern. Until a pattern has been matched, the Matcher object is in an undefined state and calling
either of these methods results in an exception of type IllegalStateException being thrown.
You usually want to find all occurrences of a pattern in a string. When you call the find() method,
searching starts either at the beginning of this matcher's region, or at the first character not searched by a
previous call to find() . Thus, you can easily find all occurrences of the pattern by searching in a loop like
this:
while(m.find()) {
System.out.println(" Start: " + m.start() + " End: " + m.end());
}