Java String regionMatches() Method

In Java, regionMatches() method of the String class compares parts (regions) of two strings to see if they match. It offers both case-sensitive and case-insensitive comparison options. This method is commonly used in string matching and validation tasks in the Java programming.

Example:

// Java Program to demonstrate regionMatches() method
public class RegionMatches {
  
    public static void main(String[] args) {
      
        // Create two string objects
        String s1 = "Hello, welcome to Java!";
        String s2 = "welcome";

        // Compare substring of s1 and s2
        boolean res = s1.regionMatches(7, s2, 0, 7);

        System.out.println("" + res);
    }
}

true

Explanation: In the above example, the method compares a region of s1 starting from index 7 with s2 starting from index 0. It checks if the first 7 characters of s1 match with s2, and the result is true because "welcome" in s1 matches s2.

Syntax of regionMatches() Method

1. Case-sensitive comparison:

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

2. Case-insensitive comparison:

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

Parameters:

• ignoreCase: If true, the comparison ignores case sensitivity.
• toffset: The starting offset of the subregion in the first string (this).
• other: The second string to compare against.
• offset: The starting offset of the subregion in the second string.
• len: The length of the substring to compare.

Return Value: The method returns true if the substrings of both strings, starting from the given offsets and of the specified length, are equal. The comparison is case-sensitive unless ignoreCase is true.

Example 1: Case-Sensitive Comparison

// Java Program to compare substrings of 
// two strings (case-sensitive)
public class CheckRegions {
  
    public static void main(String args[]) {
      
        // Create three string objects
        String s1 = new String("Welcome to Geeksforgeeks.com");
        String s2 = new String("Geeksforgeeks");
        String s3 = new String("GEEKSFORGEEKS");
        
        // Compare substring of s1 with s2
        System.out.print("Result: ");
        System.out.println(s1.regionMatches(11, s2, 0, 13)); 
        
        // Compare substring of s1 with s3
        System.out.print("Result: ");
        System.out.println(s1.regionMatches(11, s3, 0, 13)); 
        
        // Compare substring of s2 with s3
        System.out.print("Result: ");
        System.out.println(s2.regionMatches(0, s3, 0, 13)); 
    }
}

Result: true
Result: false
Result: false

Explanation: In the above example, the s1.regionMatches(11, s2, 0, 13) compares characters from index 11 of s1 with the first 13 characters of s2. It returns true because the substrings match. The s1.regionMatches(11, s3, 0, 13) compares the substrings, but case differences cause it to return false. The s2.regionMatches(0, s3, 0, 13) also returns false due to case differences.

Example 2: Case-Insensitive Comparison

// Java Program to compare substrings of 
// two strings (case-insensitive)
public class CheckRegions {
  
    public static void main(String args[]) {
      
        // Create three string objects
        String s1 = new String("Java");
        String s2 = new String("java");
        String s3 = new String("JAVA");
        
        // Compare substrings of s1 and s2 (ignoring case)
        System.out.print("Result: ");
        System.out.println(s1.regionMatches(true, 0, s2, 0, 3)); 
        
        // Compare substrings of s1 and s3 (case-sensitive)
        System.out.print("Result: ");
        System.out.println(s1.regionMatches(false, 0, s3, 0, 3)); 
        
        // Compare substrings of s2 and s3 (ignoring case)
        System.out.print("Result: ");
        System.out.println(s2.regionMatches(true, 0, s3, 0, 3));
    }
}

Result: true
Result: false
Result: true

Explanation: In this example, s1.regionMatches(true, 0, s2, 0, 3) compares "Java" and "java" (ignoring case), returning true. The s1.regionMatches(false, 0, s3, 0, 3) compares "Java" and "JAVA" (case-sensitive) and returns false. Finally, s2.regionMatches(true, 0, s3, 0, 3) compares "java" and "JAVA" (ignoring case) and returns true.