A regular expression, often called a pattern, is an expression that describes a set of strings. They are usually used to give a concise description of a set, without having to list all elements

i will stady :)


N java wy see this

Class Pattern

java.lang.Object
java.util.regex.Pattern

All Implemented Interfaces:

Serializable

public final class Pattern
extends Object
implements Serializable

A compiled representation of a regular expression.

A regular expression, specified as a string, must first be compiled into an instance of this class. The resulting pattern can then be used to create a Matcher object that can match arbitrary character sequences against the regular expression. All of the state involved in performing a match resides in the matcher, so many matchers can share the same pattern.

A typical invocation sequence is thus

Pattern p = Pattern.compile("a*b");
Matcher m = p.matcher("aaaaab");
boolean b = m.matches

A matches method is defined by this class as a convenience for when a regular expression is used just once. This method compiles an expression and matches an input sequence against it in a single invocation. The statement

 boolean b = Pattern.matches("a*b", "aaaaab");

is equivalent to the three statements above, though for repeated matches it is less efficient since it does not allow the compiled pattern to be reused. Instances of this class are immutable and are safe for use by multiple concurrent threads. Instances of the Matcher class are not safe for such use.