I've encountered an interesting scenario. For some reason strip() against blank string (contains whitespaces only) significantly faster than trim() in Java 11.
Benchmark
public class Test {
public static final String TEST_STRING = " "; // 3 whitespaces
@Benchmark
@Warmup(iterations = 10, time = 200, timeUnit = MILLISECONDS)
@Measurement(iterations = 20, time = 500, timeUnit = MILLISECONDS)
@BenchmarkMode(Mode.Throughput)
public void testTrim() {
TEST_STRING.trim();
}
@Benchmark
@Warmup(iterations = 10, time = 200, timeUnit = MILLISECONDS)
@Measurement(iterations = 20, time = 500, timeUnit = MILLISECONDS)
@BenchmarkMode(Mode.Throughput)
public void testStrip() {
TEST_STRING.strip();
}
public static void main(String[] args) throws Exception {
org.openjdk.jmh.Main.main(args);
}
}
Results
# Run complete. Total time: 00:04:16
Benchmark Mode Cnt Score Error Units
Test.testStrip thrpt 200 2067457963.295 ± 12353310.918 ops/s
Test.testTrim thrpt 200 402307182.894 ± 4559641.554 ops/s
Apparently strip() outperforms trim() ~5 times.
Although for non-blank string, results are almost identical:
public class Test {
public static final String TEST_STRING = " Test String ";
@Benchmark
@Warmup(iterations = 10, time = 200, timeUnit = MILLISECONDS)
@Measurement(iterations = 20, time = 500, timeUnit = MILLISECONDS)
@BenchmarkMode(Mode.Throughput)
public void testTrim() {
TEST_STRING.trim();
}
@Benchmark
@Warmup(iterations = 10, time = 200, timeUnit = MILLISECONDS)
@Measurement(iterations = 20, time = 500, timeUnit = MILLISECONDS)
@BenchmarkMode(Mode.Throughput)
public void testStrip() {
TEST_STRING.strip();
}
public static void main(String[] args) throws Exception {
org.openjdk.jmh.Main.main(args);
}
}
# Run complete. Total time: 00:04:16
Benchmark Mode Cnt Score Error Units
Test.testStrip thrpt 200 126939018.461 ± 1462665.695 ops/s
Test.testTrim thrpt 200 141868439.680 ± 1243136.707 ops/s
How come? Is this a bug or am I doing it wrong?
Testing environment
- CPU - Intel Xeon E3-1585L v5 @3.00 GHz
- OS - Windows 7 SP 1 64-bit
- JVM - Oracle JDK 11.0.1
- Benchamrk - JMH v 1.19
Update
Added more performance tests for different Strings (empty, blank, etc).
Benchmark
@Warmup(iterations = 5, time = 1, timeUnit = SECONDS)
@Measurement(iterations = 5, time = 1, timeUnit = SECONDS)
@Fork(value = 3)
@BenchmarkMode(Mode.Throughput)
public class Test {
private static final String BLANK = ""; // Blank
private static final String EMPTY = " "; // 3 spaces
private static final String ASCII = " abc "; // ASCII characters only
private static final String UNICODE = " абв "; // Russian Characters
private static final String BIG = EMPTY.concat("Test".repeat(100)).concat(EMPTY);
@Benchmark
public void blankTrim() {
BLANK.trim();
}
@Benchmark
public void blankStrip() {
BLANK.strip();
}
@Benchmark
public void emptyTrim() {
EMPTY.trim();
}
@Benchmark
public void emptyStrip() {
EMPTY.strip();
}
@Benchmark
public void asciiTrim() {
ASCII.trim();
}
@Benchmark
public void asciiStrip() {
ASCII.strip();
}
@Benchmark
public void unicodeTrim() {
UNICODE.trim();
}
@Benchmark
public void unicodeStrip() {
UNICODE.strip();
}
@Benchmark
public void bigTrim() {
BIG.trim();
}
@Benchmark
public void bigStrip() {
BIG.strip();
}
public static void main(String[] args) throws Exception {
org.openjdk.jmh.Main.main(args);
}
}
Results
# Run complete. Total time: 00:05:23
Benchmark Mode Cnt Score Error Units
Test.asciiStrip thrpt 15 356846913.133 ± 4096617.178 ops/s
Test.asciiTrim thrpt 15 371319467.629 ± 4396583.099 ops/s
Test.bigStrip thrpt 15 29058105.304 ± 1909323.104 ops/s
Test.bigTrim thrpt 15 28529199.298 ± 1794655.012 ops/s
Test.blankStrip thrpt 15 1556405453.206 ± 67230630.036 ops/s
Test.blankTrim thrpt 15 1587932109.069 ± 19457780.528 ops/s
Test.emptyStrip thrpt 15 2126290275.733 ± 23402906.719 ops/s
Test.emptyTrim thrpt 15 406354680.805 ± 14359067.902 ops/s
Test.unicodeStrip thrpt 15 37320438.099 ± 399421.799 ops/s
Test.unicodeTrim thrpt 15 88226653.577 ± 1628179.578 ops/s
Testing environment is the same.
Only one interesting finding. String which contains Unicode characters getting trim()'ed faster than strip()'ed
On OpenJDK 11.0.1 String.strip() (actually StringLatin1.strip()) optimizes stripping to an empty String by returning an interned String constant:
public static String strip(byte[] value) {
int left = indexOfNonWhitespace(value);
if (left == value.length) {
return "";
}
while String.trim() (actually StringLatin1.trim()) always allocates a new String object. In your example st = 3 and len = 3 so
return ((st > 0) || (len < value.length)) ?
newString(value, st, len - st) : null;
will under the hood copy the array and creates a new String object
return new String(Arrays.copyOfRange(val, index, index + len),
LATIN1);
Making above assumption we can update the benchmark to compare against a non-empty String which shouldn't be affected by mentioned String.strip() optimization:
@Warmup(iterations = 10, time = 200, timeUnit = MILLISECONDS)
@Measurement(iterations = 20, time = 500, timeUnit = MILLISECONDS)
@BenchmarkMode(Mode.Throughput)
public class MyBenchmark {
public static final String EMPTY_STRING = " "; // 3 whitespaces
public static final String NOT_EMPTY_STRING = " a "; // 3 whitespaces with a in the middle
@Benchmark
public void testEmptyTrim() {
EMPTY_STRING.trim();
}
@Benchmark
public void testEmptyStrip() {
EMPTY_STRING.strip();
}
@Benchmark
public void testNotEmptyTrim() {
NOT_EMPTY_STRING.trim();
}
@Benchmark
public void testNotEmptyStrip() {
NOT_EMPTY_STRING.strip();
}
}
Running it shows no significant difference between strip() and trim() for a non-empty String. Oddly enough trimming to an empty String is still the slowest:
Benchmark Mode Cnt Score Error Units
MyBenchmark.testEmptyStrip thrpt 100 1887848947.416 ± 257906287.634 ops/s
MyBenchmark.testEmptyTrim thrpt 100 206638996.217 ± 57952310.906 ops/s
MyBenchmark.testNotEmptyStrip thrpt 100 399701777.916 ± 2429785.818 ops/s
MyBenchmark.testNotEmptyTrim thrpt 100 385144724.856 ± 3928016.232 ops/s