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8265237: String.join and StringJoiner can be improved further

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Reviewed-by: rriggs, redestad
This commit is contained in:
Peter Levart 2021-04-21 10:32:03 +00:00
parent ed477da9c6
commit 98cb81b381
6 changed files with 197 additions and 40 deletions
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72
src/java.base/share/classes/java/lang/String.java
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@ -43,7 +43,6 @@ import java.util.Locale;
import java.util.Objects;
import java.util.Optional;
import java.util.Spliterator;
import java.util.StringJoiner;
import java.util.function.Function;
import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;
@ -51,6 +50,8 @@ import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;
import jdk.internal.vm.annotation.ForceInline;
import jdk.internal.vm.annotation.IntrinsicCandidate;
import jdk.internal.vm.annotation.Stable;
import sun.nio.cs.ArrayDecoder;
@ -3218,14 +3219,58 @@ public final class String
* @since 1.8
*/
public static String join(CharSequence delimiter, CharSequence... elements) {
Objects.requireNonNull(delimiter);
Objects.requireNonNull(elements);
// Number of elements not likely worth Arrays.stream overhead.
StringJoiner joiner = new StringJoiner(delimiter);
for (CharSequence cs: elements) {
joiner.add(cs);
var delim = delimiter.toString();
var elems = new String[elements.length];
for (int i = 0; i < elements.length; i++) {
elems[i] = String.valueOf(elements[i]);
}
return joiner.toString();
return join("", "", delim, elems, elems.length);
}
/**
* Designated join routine.
*
* @param prefix the non-null prefix
* @param suffix the non-null suffix
* @param delimiter the non-null delimiter
* @param elements the non-null array of non-null elements
* @param size the number of elements in the array (<= elements.length)
* @return the joined string
*/
@ForceInline
static String join(String prefix, String suffix, String delimiter, String[] elements, int size) {
int icoder = prefix.coder() | suffix.coder() | delimiter.coder();
long len = (long) prefix.length() + suffix.length() + (long) Math.max(0, size - 1) * delimiter.length();
// assert len > 0L; // max: (long) Integer.MAX_VALUE << 32
// following loop wil add max: (long) Integer.MAX_VALUE * Integer.MAX_VALUE to len
// so len can overflow at most once
for (int i = 0; i < size; i++) {
var el = elements[i];
len += el.length();
icoder |= el.coder();
}
byte coder = (byte) icoder;
// long len overflow check, char -> byte length, int len overflow check
if (len < 0L || (len <<= coder) != (int) len) {
throw new OutOfMemoryError("Requested string length exceeds VM limit");
}
byte[] value = StringConcatHelper.newArray(len);
int off = 0;
prefix.getBytes(value, off, coder); off += prefix.length();
if (size > 0) {
var el = elements[0];
el.getBytes(value, off, coder); off += el.length();
for (int i = 1; i < size; i++) {
delimiter.getBytes(value, off, coder); off += delimiter.length();
el = elements[i];
el.getBytes(value, off, coder); off += el.length();
}
}
suffix.getBytes(value, off, coder);
// assert off + suffix.length() == value.length >> coder;
return new String(value, coder);
}
/**
@ -3266,11 +3311,16 @@ public final class String
Iterable<? extends CharSequence> elements) {
Objects.requireNonNull(delimiter);
Objects.requireNonNull(elements);
StringJoiner joiner = new StringJoiner(delimiter);
var delim = delimiter.toString();
var elems = new String[8];
int size = 0;
for (CharSequence cs: elements) {
joiner.add(cs);
if (size >= elems.length) {
elems = Arrays.copyOf(elems, elems.length << 1);
}
elems[size++] = String.valueOf(cs);
}
return joiner.toString();
return join("", "", delim, elems, size);
}
/**