Use Java's String.matches() function to determine whether a string matches a specified regular expression

Use Java's String.matches() function to determine whether a string matches a specified regular expression

In Java, we often need to perform some pattern matching operations on strings. Regular expressions are a very powerful tool for describing and matching string patterns. The String class in Java provides a very convenient method matches() to determine whether a string matches a specified regular expression.

Let's take a look at how to use the String.matches() function to determine whether a string matches a regular expression, and understand its usage through some sample code.

First of all, we need to clarify the definition of the String.matches() function:
boolean matches(String regex)
This method matches the given regular expression with a string. A return value of true indicates a successful match, otherwise it indicates a failed match.

Next, let’s look at some sample codes to better understand how to use the String.matches() function:

Example 1: Determine whether to match a mobile phone number

public class StringMatchExample {
    public static void main(String[] args) {
        String phoneNumber1 = "12345678900";
        String phoneNumber2 = "0987654321";
        String phoneNumber3 = "1234567";
        
        String regex = "1[345789]\d{9}";
        
        System.out.println(phoneNumber1.matches(regex)); // true
        System.out.println(phoneNumber2.matches(regex)); // false
        System.out.println(phoneNumber3.matches(regex)); // false
    }
}

In the above example, we defined a regular expression 1[345789]\d{9} to match mobile phone numbers in mainland China. We use three string variables phoneNumber1, phoneNumber2 and phoneNumber3 to test whether they match. According to the running results, it can be seen that phoneNumber1 matches successfully, but phoneNumber2 and phoneNumber3 fail to match.

Example 2: Determine whether it matches the email address

public class StringMatchExample {
    public static void main(String[] args) {
        String email1 = "abc123@gmail.com";
        String email2 = "abc@123@gmail.com";
        String email3 = "abc123@.com";
        
        String regex = "\w+@(\w+.)+[a-z]{2,3}";
        
        System.out.println(email1.matches(regex)); // true
        System.out.println(email2.matches(regex)); // false
        System.out.println(email3.matches(regex)); // false
    }
}

In the above example, we use the regular expression\w @(\w .) [a-z]{2,3 } to match email addresses. We use three string variables email1, email2 and email3 to test whether they match. According to the running results, you can see that email1 matches successfully, but email2 and email3 fail.

Through the above two sample codes, we can see that it is very simple to use the String.matches() function to determine whether a string matches a specified regular expression. You only need to pass the target string and regular expression as parameters to the matches() function, and the function will return a boolean type result to indicate whether the match is successful.

It should be noted that when using the String.matches() function to determine whether a string matches a regular expression, you need to ensure that the entire string exactly matches the regular expression. If the string is only partially matched, false will also be returned.

In addition to the String.matches() function, Java also provides some other regular expression matching methods, such as String.match(), Pattern class, Matcher class, etc. These methods may be more flexible and convenient to use in complex regular expression applications.

In actual development, regular expressions are widely used. By using the String.matches() function to determine whether a string matches a specified regular expression, we can effectively perform data verification, formatting, matching and other operations. I hope the explanations and examples in this article can help you better understand and use the String.matches() function.

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