Here, pattern is the regular expression that you want to use. The compile( ) method transforms
the string in pattern into a pattern that can be used for pattern matching by the Matcher class.
It returns a Pattern object that contains the pattern.
Once you have created a Pattern object, you will use it to create a Matcher. This is done
by calling the matcher( ) factory method defined by Pattern. It is shown here:
Matcher matcher(CharSequence str)
Here str is the character sequence that the pattern will be matched against. This is called the
input sequence. CharSequence is an interface that defines a read-only set of characters. It is
implemented by the String class, among others. Thus, you can pass a string to matcher( ).
Matcher
The Matcher class has no constructors. Instead, you create a Matcher by calling the matcher( )
factory method defined by Pattern, as just explained. Once you have created a Matcher, you
will use its methods to perform various pattern matching operations.
The simplest pattern matching method is matches( ), which simply determines whether
the character sequence matches the pattern. It is shown here:
boolean matches( )
It returns true if the sequence and the pattern match, and false otherwise. Understand that
the entire sequence must match the pattern, not just a subsequence of it.
To determine if a subsequence of the input sequence matches the pattern, use find( ).
One version is shown here:
boolean find( )
It returns true if there is a matching subsequence and false otherwise. This method can be
called repeatedly, allowing it to find all matching subsequences. Each call to find( ) begins
where the previous one left off.
You can obtain a string containing the last matching sequence by calling group( ). One
of its forms is shown here:
String group( )
The matching string is returned. If no match exists, then an IllegalStateException is thrown.
You can obtain the index within the input sequence of the current match by calling
start( ). The index one past the end of the current match is obtained by calling end( ). These
methods are shown here:
int start( )
int end( )
Both throw IllegalStateException if no match exists.
You can replace all occurrences of a matching sequence with another sequence by
calling replaceAll( ), shown here:
String replaceAll(String newStr)
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