Java PatternSyntaxException Class getIndex() Method with Examples

Java PatternSyntaxException Class is defined under the java.util.regex package and it depicts unchecked exception that signifies syntax error in a regular expression pattern. This class can be declared using the below syntax,

public class PatternSyntaxException extends IllegalArgumentException

PatternSyntaxException::getIndex()

This method is used to retrieve the index of the error which is thrown as an exception. The syntax is given below,

Syntax:

public int getIndex()

Returns: It returns a non-negative integer: The index in the pattern of the error is -1 if the index cannot be retrieved

Example 1: In this example, the error is at the index 0 in the pattern. This is because of the unclosed character.  

Java

// Java program to illustrate the working of getIndex() method

import java.io.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;

class GFG {


   private static String regularExpression = "[";
   private static String input = "GeeksforGeeks " + "is a learning platform.";
   private static String replace = "Hi";

    public static void main (String[] args) {

try{
         // Compile the pattern
         Pattern pattern = Pattern.compile(regularExpression);

         // To get a matcher object
         Matcher matcher = pattern.matcher(input);
         input = matcher.replaceAll(replace);
      } catch(PatternSyntaxException e){

         // Print the index in the error of the pattern
         System.out.println("Index: "+ e.getIndex());
         System.out.println("Message: "+ e.getMessage());
      }
    }
}

Output

Index: 0
Message: Unclosed character class near index 0
[
^

Example 2: In this example, getIndex() method returns -1. This is because of illegal repetition the index cannot be retrieved. 

Java

// Java program to illustrate the working of getIndex() method

import java.io.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;

class GFG {

   // Declaring a string variable to store the regular expression
   private static String regularExpression = "{";
   private static String input = "GeeksforGeeks " + "is a learning platform.";
   private static String replace = "Hello";

    public static void main (String[] args) {

         try{

         // Compile the pattern
         Pattern pattern = Pattern.compile(regularExpression);

         // To get a matcher object
         Matcher matcher = pattern.matcher(input);
         input = matcher.replaceAll(replace);
      } catch(PatternSyntaxException e){

         // Print the index in the error of the pattern
         System.out.println("Index: "+ e.getIndex());
         System.out.println("Message: "+ e.getMessage());
      }
    }
}

Output

Index: -1
Message: Illegal repetition
{