Methods of the PatternSyntaxException Class

Methods of the PatternSyntaxException Class

A PatternSyntaxException is an unchecked exception that indicates a syntax error in a regular expression pattern. The PatternSyntaxException class provides the following methods to help you determine what went wrong:

• public String getDescription(): Retrieves the description of the error.
• public int getIndex(): Retrieves the error index.
• public String getPattern(): Retrieves the erroneous regular expression pattern.
• public String getMessage(): Returns a multi-line string containing the description of the syntax error and its index, the erroneous regular-expression pattern, and a visual indication of the error index within the pattern.

The following source code updates our previous test harness to check for malformed regular expressions:

To run this test, enter ?i)foo as the regular expression. This mistake is a common scenario in which the programmer has forgotten the opening parenthesis in the embedded flag expression (?i). Doing so will produce the following results:

From this output, we can see that the syntax error is a dangling metacharacter (the question mark) at index 0. A missing opening parenthesis is the culprit.