Java regionMatches Example and Performance

Use the regionMatches string method to test parts of strings. Avoid creating substrings.

RegionMatches. This method tests a region of one string against another. We provide a start index for both strings. We also provide a length argument (the number of chars to test on both).

With regionMatches, we can see if a substring patches another substring. We can avoid creating substrings. This saves allocations and improves performance.

An example. Let us begin with this example. We have a string literal with four concatenated words in it. We match each part of this literal.

Case: We can have regionMatches ignore the case of characters by passing a value of "true" as the first argument.

Java program that uses regionMatches public class Program { public static void main(String[] args) { String codes = "onetwothreeFour"; // Check for "two" at index 3. // ... Length is 3 chars. if (codes.regionMatches(3, "two", 0, 3)) { System.out.println(true); } // Check for "three" at index 6. // ... Length is 5 chars. if (codes.regionMatches(6, "three", 0, 5)) { System.out.println(true); } // Check for "FOUR" from "IS_FOUR" at index 11. // ... Length is 4 chars. if (codes.regionMatches(true, 11, "IS_FOUR", 3, 4)) { System.out.println(true); } } } Output true true true

Benchmark. Here is a benchmark of regionMatches. We can use regionMatches for some significant performance wins in real-world Java programs.

Version 1: In this version of the code, we use the regionMatches method to compare 2 substring parts.

Version 2: In this code we make two substring calls. Those substrings are compared with equals().

Equals

Result: RegionMatches is faster. In this benchmark regionMatches is over 10 times faster than the version that uses substring and equals.

Java program that benchmarks regionMatches public class Program { public static void main(String[] args) { String part1 = "catdogbird"; String part2 = "dogbirdcat"; // Test two versions. if (part1.regionMatches(3, part2, 0, 3)) { System.out.println("True 1"); } if (part1.substring(3, 6).equals(part2.substring(0, 3))) { System.out.println("True 2"); } int count = 0; long t1 = System.currentTimeMillis(); // Version 1: use regionMatches to compare two substrings. for (int i = 0; i < 10000000; i++) { if (part1.regionMatches(3, part2, 0, 3)) { count++; } } long t2 = System.currentTimeMillis(); // Version 2: use substring to compare two substrings. for (int i = 0; i < 10000000; i++) { if (part1.substring(3, 6).equals(part2.substring(0, 3))) { count++; } } long t3 = System.currentTimeMillis(); // ... Times. System.out.println(count); System.out.println(t2 - t1); System.out.println(t3 - t2); } } Output True 1 True 2 20000000 15 ms: regionMatches 172 ms: substring, equals

Notes, indexes. When using methods like regionMatches and substring(), using correct indexes and lengths is important. The final argument on regionMatches is a length.Substring length

Performance. Avoiding allocations is one of the best performance optimizations. With regionMatches, we can achieve a big performance win if we can reduce substring allocations.

A summary. The arguments to regionMatches can be hard to get right at first. But the performance and code size improvements with regionMatches makes it worth the effort.

The Dev Codes

.Net

.NET Array Dictionary List String 2D Async DataTable Dates DateTime Enum File For Foreach Format IEnumerable If IndexOf Lambda LINQ Parse Path Process Property Regex Replace Sort Split Static StringBuilder Substring Switch Tuple

Java

Core Array ArrayList HashMap String 2D Cast Character Console Deque Duplicates File For Format HashSet If IndexOf Lambda Math ParseInt Process Random Regex Replace Sort Split StringBuilder Substring Switch Vector While

TheDeveloperBlog.com

Java regionMatches Example and Performance

Related Links:

.Net

Java

Related Links