Java String regionMatches() Method

The String.regionMatches() method in Java is used to compare specific regions of two strings for equality.

Table of Contents

1. Introduction
2. regionMatches Method Syntax
3. Examples
   • Basic Usage
   • Using regionMatches with Case Insensitivity
   • Handling Edge Cases
   • Real-World Use Case
4. Conclusion

Introduction

The String.regionMatches() method is a member of the String class in Java. It allows you to compare specific regions of two strings to determine if they are equal. This method is useful when you need to compare substrings within larger strings.

regionMatches() Method Syntax

There are two overloaded versions of the regionMatches method:

Case-Sensitive Comparison

public boolean regionMatches(int toffset, String other, int ooffset, int len)

• toffset: The starting index of the region in the current string.
• other: The string to compare.
• ooffset: The starting index of the region in the other string.
• len: The number of characters to compare.

Case-Insensitive Comparison

public boolean regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len)

• ignoreCase: If true, the comparison ignores case; otherwise, the comparison is case-sensitive.
• toffset: The starting index of the region in the current string.
• other: The string to compare.
• ooffset: The starting index of the region in the other string.
• len: The number of characters to compare.

Examples

Basic Usage

The regionMatches method can be used to compare specific regions of two strings.

Example

public class RegionMatchesExample {
    public static void main(String[] args) {
        String str1 = "Hello, World!";
        String str2 = "World";

        boolean result = str1.regionMatches(7, str2, 0, 5);
        System.out.println("Regions match: " + result);
    }
}

Output:

Regions match: true

Using regionMatches with Case Insensitivity

The regionMatches method can also be used to compare regions of two strings, ignoring case differences.

Example

public class RegionMatchesIgnoreCaseExample {
    public static void main(String[] args) {
        String str1 = "Hello, World!";
        String str2 = "world";

        boolean result = str1.regionMatches(true, 7, str2, 0, 5);
        System.out.println("Regions match (case-insensitive): " + result);
    }
}

Output:

Regions match (case-insensitive): true

Handling Edge Cases

Example: Regions Out of Bound

If the specified regions are out of bounds, the regionMatches method returns false without throwing an exception.

public class RegionMatchesOutOfBoundsExample {
    public static void main(String[] args) {
        String str1 = "Hello, World!";
        String str2 = "Hello";

        boolean result = str1.regionMatches(12, str2, 0, 5);
        System.out.println("Regions match (out of bounds): " + result);
    }
}

Output:

Regions match (out of bounds): false

Example: Comparing Different Lengths

If the length of the region to be compared exceeds the length of either string, the regionMatches method returns false.

public class RegionMatchesDifferentLengthsExample {
    public static void main(String[] args) {
        String str1 = "Hello, World!";
        String str2 = "Hello, Java!";

        boolean result = str1.regionMatches(0, str2, 0, 15);
        System.out.println("Regions match (different lengths): " + result);
    }
}

Output:

Regions match (different lengths): false

Real-World Use Case

Example: Validating Substrings within Larger Strings

One common use case for regionMatches is validating that a specific part of a string matches a given pattern or substring.

public class ValidateSubstringExample {
    public static void main(String[] args) {
        String url = "https://www.example.com";
        String protocol = "https";

        if (url.regionMatches(true, 0, protocol, 0, protocol.length())) {
            System.out.println("The URL uses HTTPS.");
        } else {
            System.out.println("The URL does not use HTTPS.");
        }
    }
}

Output:

The URL uses HTTPS.

In this example, the regionMatches method is used to check if the URL starts with the "https" protocol, ignoring case differences.

Conclusion

The String.regionMatches() method in Java is used for comparing specific regions of two strings. It supports both case-sensitive and case-insensitive comparisons, making it versatile for various applications. This method is particularly useful for validating and comparing substrings within larger strings. By understanding and utilizing the regionMatches method, you can efficiently manage string region comparisons in your Java programs.