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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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43
src/java.base/share/classes/java/util/StringJoiner.java
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@ -24,6 +24,9 @@
*/
package java.util;
import jdk.internal.access.JavaLangAccess;
import jdk.internal.access.SharedSecrets;
/**
* {@code StringJoiner} is used to construct a sequence of characters separated
* by a delimiter and optionally starting with a supplied prefix
@ -63,6 +66,8 @@ package java.util;
* @since 1.8
*/
public final class StringJoiner {
private static final String[] EMPTY_STRING_ARRAY = new String[0];
private final String prefix;
private final String delimiter;
private final String suffix;
@ -158,27 +163,15 @@ public final class StringJoiner {
*/
@Override
public String toString() {
final String[] elts = this.elts;
if (elts == null && emptyValue != null) {
return emptyValue;
}
final int size = this.size;
final int addLen = prefix.length() + suffix.length();
var elts = this.elts;
if (size == 0) {
if (addLen == 0) {
return "";
if (emptyValue != null) {
return emptyValue;
}
return prefix + suffix;
elts = EMPTY_STRING_ARRAY;
}
final String delimiter = this.delimiter;
StringBuilder sb = new StringBuilder(len + addLen).append(prefix);
if (size > 0) {
sb.append(elts[0]);
for (int i = 1; i < size; i++) {
sb.append(delimiter).append(elts[i]);
}
}
return sb.append(suffix).toString();
return JLA.join(prefix, suffix, delimiter, elts, size);
}
/**
@ -233,7 +226,7 @@ public final class StringJoiner {
*/
public StringJoiner merge(StringJoiner other) {
Objects.requireNonNull(other);
if (other.elts == null) {
if (other.size == 0) {
return this;
}
other.compactElts();
@ -241,15 +234,11 @@ public final class StringJoiner {
}
private void compactElts() {
if (size > 1) {
StringBuilder sb = new StringBuilder(len).append(elts[0]);
int i = 1;
do {
sb.append(delimiter).append(elts[i]);
elts[i] = null;
} while (++i < size);
int sz = size;
if (sz > 1) {
elts[0] = JLA.join("", "", delimiter, elts, sz);
Arrays.fill(elts, 1, sz, null);
size = 1;
elts[0] = sb.toString();
}
}
@ -267,4 +256,6 @@ public final class StringJoiner {
return (size == 0 && emptyValue != null) ? emptyValue.length() :
len + prefix.length() + suffix.length();
}
private static final JavaLangAccess JLA = SharedSecrets.getJavaLangAccess();
}