Java Regex to extract maximum numeric value from a string

In this article, we will learn to extract the maximum numeric value from a string using Java's regex. While Java provides several ways to handle string manipulation, regular expressions (regex) offer a powerful and efficient tool for such tasks.

Problem Statement 

The maximum numeric value is extracted from an alphanumeric string. An example of this is given as follows ?

Input

String = abcd657efgh234

Output

Maximum numeric value = 657

Using Java Regex and Pattern Class 

Java provides the Pattern and Matcher classes to work with regular expressions. The Pattern class compiles a regular expression, and the Matcher class is used to find matches of the regex pattern in the target string.

• Pattern.compile(regex) method compiles the regular expression into a Pattern object.
  
• The matcher(input) method applies the compiled pattern to the input string.
  
• The while loop iterates over each match found in the string.
  
• matcher.group() retrieves the matched number (as a string), which is then parsed into an integer.

Example

Below is an example of extracting the maximum numeric value from a string using Java Regex

import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Example {
 public static void main (String[] args) {
    String str = "123abc874def235ijk999";
    System.out.println("The string is: " + str);
    String regex = "\d+";
    Pattern ptrn = Pattern.compile(regex);
    Matcher match = ptrn.matcher(str);
    int maxNum = 0;
    while(match.find()) {
       int num = Integer.parseInt(match.group());
       if(num > maxNum) {
          maxNum = num;
       }
    }
    System.out.println("The maximum numeric value in above string is: " + maxNum);
 }
}

Output

The string is: 123abc874def235ijk999
The maximum numeric value in above string is: 999

Using regex with Java Streams

With Java 8 and later, streams provide a more concise and functional programming style for handling tasks like this. The stream API makes it easy to manipulate collections, and when combined with regular expressions, it offers a very clean way to extract and process numeric values.

• The split() method splits the string by any non-digit characters (\D+). This effectively separates the numbers from the rest of the string.
  
• The isEmpty() ensures that we don't process any empty strings that result from consecutive non-digit characters.
  
• The mapToInt(Integer::parseInt) converts each numeric string into an integer.
  
• The max() method finds the maximum number in the stream, and orElse(0) ensures that if no numbers are found, we default to 0.
  

Example

import java.util.Arrays;
import java.util.regex.Pattern;
import java.util.stream.Collectors;

public class MaxNumericExtractorWithStreams {
    public static void main(String[] args) {
        String input = "abc123def456ghi789xyz000";
        System.out.println("Input String: " + input);
        
        // Use streams to extract numbers and find the maximum
        int maxNumber = Arrays.stream(input.split("\D+"))
                            .filter(s -> !s.isEmpty()) 
                            .mapToInt(Integer::parseInt) 
                            .max() 
                            .orElse(0);
        
        // Output the maximum numeric value
        System.out.println("The maximum numeric value in the string is: " + maxNumber);
    }
}

Output

Input String: abc123def456ghi789xyz000

The maximum numeric value in the string is: 789