String Matches Regex in Java

1. Use the matches() Method to Match String in Java
2. Use the regionMatches() Method to Match String in Java

The String class is one of the most used classes in Java. It provides many methods to perform various operations, and in this article, we will be talking about the methods called matches() and regionMatches() of the String class.

Use the matches() Method to Match String in Java

The matches() method matches a string with the value passed in the function. The value to pass in the function as argument should be a regular expression.

The function Pattern.matches() returns the same result as String.matches().

In the example below, we create three String variables, and we use regex (short for Regular Expression) to find out if all the characters in the String are in lowercase and valid alphabets from a to z.

The first print statement calls the matches() method and passes [a-z]+, the regex to match if the characters are lower case alphabets. The first statement outputs true because the String exampleStr1 contains the characters matching the regex.

The second statement checks the exampleStr2 with the same regex and returns false because the String’s first character is upper case.

The last print statement also returns false that checks the exampleStr3 as non-alphabetical characters exist.

public class ExampleClass1 {
  public static void main(String[] args) {
    String exampleStr1 = "guardian";
    String exampleStr2 = "Guardian";
    String exampleStr3 = "[abc]";

    System.out.println("First String: " + exampleStr1.matches("[a-z]+"));
    System.out.println("Second String: " + exampleStr2.matches("[a-z]+"));
    System.out.println("Third String: " + exampleStr3.matches("[a-z]+"));
  }
}

Output:

First String: true
Second String: false
Third String: false

Use the regionMatches() Method to Match String in Java

Another method to match a string using a regex is regionMatches(), which matches regions of two strings. The example has two Strings, the first is a five-word statement, and the second String is a single word.

Using the regionMatches() method, we match if the word production contains the substring duct. We pass four arguments in the regionMatches() function to perform this.

The first argument is the start position of the word from where to start scanning; in our case, our word is at 19th position, so we set it as starting position.

The second argument is the exampleStr2 input string we want to match.

We pass the starting position of exampleStr2 as the third argument, and the last argument specifies the number of characters to match.

public class ExampleClass1 {
  public static void main(String[] args) {
    String exampleStr1 = "this site is in production";
    String exampleStr2 = "duct";

    System.out.println(exampleStr1.regionMatches(19, exampleStr2, 0, 4));
  }
}

Output:

true

The above code only matches the substring if the matching String is of the same case. We pass another argument in the regionMatches() that ignores the case of the characters.

public class ExampleClass1 {
  public static void main(String[] args) {
    String exampleStr1 = "this site is in production";
    String exampleStr2 = "DUCT";

    System.out.println(exampleStr1.regionMatches(true, 19, exampleStr2, 0, 4));
  }
}

Output:

true