Periksa Jika String Berisi Substring

1. Ikhtisar

Dalam tutorial ini, kami akan meninjau beberapa cara untuk memeriksa apakah sebuah String berisi substring, dan kami akan membandingkan kinerja masing-masing.

2. String.indexOf

Pertama-tama, coba gunakan metode String.indexOf . indexOf memberi kita posisi pertama di mana substring ditemukan, atau -1 jika tidak ditemukan sama sekali.

Saat kami menelusuri "Rhap", ini akan menghasilkan 9:

Assert.assertEquals(9, "Bohemian Rhapsodyan".indexOf("Rhap"));

Saat kami menelusuri "rhap", itu akan mengembalikan -1 karena peka huruf besar / kecil.

Assert.assertEquals(-1, "Bohemian Rhapsodyan".indexOf("rhap")); Assert.assertEquals(9, "Bohemian Rhapsodyan".toLowerCase().indexOf("rhap"));

Penting juga untuk diperhatikan, bahwa jika kita mencari substring "an", itu akan menghasilkan 6 karena mengembalikan kemunculan pertama:

Assert.assertEquals(6, "Bohemian Rhapsodyan".indexOf("an"));

3. String.contains

Selanjutnya, mari kita coba String.contains . contains akan mencari substring di seluruh String dan akan mengembalikan true jika ditemukan dan false jika tidak.

Dalam contoh ini, berisi return true karena "Hey" ditemukan.

Assert.assertTrue("Hey Ho, let's go".contains("Hey"));

Jika string tidak ditemukan, berisi return false :

Assert.assertFalse("Hey Ho, let's go".contains("jey"));

Dalam contoh terakhir, "hey" tidak ditemukan karena String.contains peka huruf besar kecil.

Assert.assertFalse("Hey Ho, let's go".contains("hey")); Assert.assertTrue("Hey Ho, let's go".toLowerCase().contains("hey"));

Hal yang menarik adalah yang berisi panggilan internal indexOf untuk mengetahui apakah substring ada, atau tidak.

4. StringUtils.containsIgnoreCase

Pendekatan ketiga kami akan menggunakan StringUtils # containsIgnoreCase dari pustaka Apache Commons Lang :

Assert.assertTrue(StringUtils.containsIgnoreCase("Runaway train", "train")); Assert.assertTrue(StringUtils.containsIgnoreCase("Runaway train", "Train"));

Kita dapat melihat bahwa itu akan memeriksa apakah substring terkandung dalam String , mengabaikan case . Itulah mengapa containsIgnoreCase mengembalikan nilai true saat kita mencari "Trai" dan juga "trai" di dalam "Kereta Runaway".

Pendekatan ini tidak akan seefisien pendekatan sebelumnya karena membutuhkan waktu tambahan untuk mengabaikan kasus ini. containsIgnoreCase secara internal mengubah setiap huruf menjadi huruf besar dan membandingkan huruf yang dikonversi alih-alih yang asli.

5. Menggunakan Pola

Pendekatan terakhir kami akan menggunakan Pola dengan ekspresi reguler :

Pattern pattern = Pattern.compile("(?

We can observe that we need to build the Pattern first, then we need to create the Matcher, and finally, we can check with the find method if there's an occurrence of the substring or not:

Matcher matcher = pattern.matcher("Hit the road Jack"); Assert.assertTrue(matcher.find());

For example, the first time that find is executed, it returns true because the word “road” is contained inside of the string “Hit the road Jack”, but when we try to find the same word in the string “and don't you come back no more” it returns false:

Matcher matcher = pattern.matcher("and don't you come back no more"); Assert.assertFalse(matcher.find());

6. Performance Comparison

We'll use an open-source micro-benchmark framework called Java Microbenchmark Harness (JMH) in order to decide which method is the most efficient in terms of execution time.

6.1. Benchmark Setup

As in every JMH benchmark, we have the ability to write a setup method, in order to have certain things in place before our benchmarks are run:

@Setup public void setup() { message = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, " + "sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. " + "Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris " + "nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in " + "reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. " + "Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt " + "mollit anim id est laborum"; pattern = Pattern.compile("(?

In the setup method, we're initializing the message field. We'll use this as the source text for our various searching implementations.

We also are initializing pattern in order to use it later in one of our benchmarks.

6.2. The String.indexOf Benchmark

Our first benchmark will use indexOf:

@Benchmark public int indexOf() { return message.indexOf("eiusmod"); }

We'll search in which position “eiusmod” is present in the message variable.

6.3. The String.contains Benchmark

Our second benchmark will use contains:

@Benchmark public boolean contains() { return message.contains("eiusmod"); }

We'll try to find if the message value contains “eiusmod”, the same substring used in the previous benchmark.

6.4. The StringUtils.containsIgnoreCase Benchmark

Our third benchmark will use StringUtils#containsIgnoreCase:

@Benchmark public boolean containsStringUtilsIgnoreCase() { return StringUtils.containsIgnoreCase(message, "eiusmod"); }

As with the previous benchmarks, we'll search the substring in the message value.

6.5. The Pattern Benchmark

And our last benchmark will use Pattern:

@Benchmark public boolean searchWithPattern() { return pattern.matcher(message).find(); }

We'll use the pattern initialized in the setup method to create a Matcher and be able to call the find method, using the same substring as before.

6.6. Analysis of Benchmarks Results

It's important to note that we're evaluating the benchmark results in nanoseconds.

After running our JMH test, we can see the average time each took:

  • contains: 14.736 ns
  • indexOf: 14.200 ns
  • containsStringUtilsIgnoreCase: 385.632 ns
  • searchWithPattern: 1014.633 ns

indexOf method is the most efficient one, closely followed by contains. It makes sense that contains took longer because is using indexOf internally.

containsStringUtilsIgnoreCase took extra time compared with the previous ones because it's case insensitive.

searchWithPattern, took an even higher average time the last one, proving that using Patterns is the worst alternative for this task.

7. Conclusion

In this article, we've explored various ways to search for a substring in a String. We've also benchmarked the performance of the different solutions.

As always, the code is available over on GitHub.