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[LANG-1805] Optimize StringBuilder usage in join() for primitives #1532

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[LANG-1805] Optimize StringBuilder usage in join() for primitives #1532

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e97b358
[LANG-1805] Fix inaccurate capacity calculation in join(boolean[])
jher235 Dec 17, 2025
b485755
[LANG-1805] Fix inaccurate capacity calculation in join(char[])
jher235 Dec 17, 2025
6f62ba9
[LANG-1805] Optimize StringBuilder usage in join() for primitives
jher235 Dec 17, 2025
c798cb4
[LANG-1805] Add JMH benchmark for StringUtils.join on primitive arrays
jher235 Dec 18, 2025
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112 changes: 64 additions & 48 deletions src/main/java/org/apache/commons/lang3/StringUtils.java
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Original file line number Diff line number Diff line change
Expand Up @@ -3857,16 +3857,18 @@ public static String join(final boolean[] array, final char delimiter, final int
if (array == null) {
return null;
}
if (endIndex - startIndex <= 0) {
final int noOfItems = endIndex - startIndex;
if (noOfItems <= 0) {
return EMPTY;
}
final StringBuilder stringBuilder = new StringBuilder(array.length * 5 + array.length - 1);
for (int i = startIndex; i < endIndex; i++) {
final StringBuilder stringBuilder = new StringBuilder(noOfItems * 5 + noOfItems - 1);
stringBuilder.append(array[startIndex]);
for (int i = startIndex + 1; i < endIndex; i++) {
stringBuilder
.append(array[i])
.append(delimiter);
.append(delimiter)
.append(array[i]);
}
return stringBuilder.substring(0, stringBuilder.length() - 1);
return stringBuilder.toString();
}

/**
Expand Down Expand Up @@ -3932,16 +3934,18 @@ public static String join(final byte[] array, final char delimiter, final int st
if (array == null) {
return null;
}
if (endIndex - startIndex <= 0) {
final int noOfItems = endIndex - startIndex;
if (noOfItems <= 0) {
return EMPTY;
}
final StringBuilder stringBuilder = new StringBuilder();
for (int i = startIndex; i < endIndex; i++) {
final StringBuilder stringBuilder = new StringBuilder(noOfItems * 4);
stringBuilder.append(array[startIndex]);
for (int i = startIndex + 1; i < endIndex; i++) {
stringBuilder
.append(array[i])
.append(delimiter);
.append(delimiter)
.append(array[i]);
}
return stringBuilder.substring(0, stringBuilder.length() - 1);
return stringBuilder.toString();
}

/**
Expand Down Expand Up @@ -4007,16 +4011,18 @@ public static String join(final char[] array, final char delimiter, final int st
if (array == null) {
return null;
}
if (endIndex - startIndex <= 0) {
final int noOfItems = endIndex - startIndex;
if (noOfItems <= 0) {
return EMPTY;
}
final StringBuilder stringBuilder = new StringBuilder(array.length * 2 - 1);
for (int i = startIndex; i < endIndex; i++) {
final StringBuilder stringBuilder = new StringBuilder(noOfItems * 2 - 1);
stringBuilder.append(array[startIndex]);
for (int i = startIndex + 1; i < endIndex; i++) {
stringBuilder
.append(array[i])
.append(delimiter);
.append(delimiter)
.append(array[i]);
}
return stringBuilder.substring(0, stringBuilder.length() - 1);
return stringBuilder.toString();
}

/**
Expand Down Expand Up @@ -4082,16 +4088,18 @@ public static String join(final double[] array, final char delimiter, final int
if (array == null) {
return null;
}
if (endIndex - startIndex <= 0) {
final int noOfItems = endIndex - startIndex;
if (noOfItems <= 0) {
return EMPTY;
}
final StringBuilder stringBuilder = new StringBuilder();
for (int i = startIndex; i < endIndex; i++) {
final StringBuilder stringBuilder = new StringBuilder(noOfItems * 10);
stringBuilder.append(array[startIndex]);
for (int i = startIndex + 1; i < endIndex; i++) {
stringBuilder
.append(array[i])
.append(delimiter);
.append(delimiter)
.append(array[i]);
}
return stringBuilder.substring(0, stringBuilder.length() - 1);
return stringBuilder.toString();
}

/**
Expand Down Expand Up @@ -4157,16 +4165,18 @@ public static String join(final float[] array, final char delimiter, final int s
if (array == null) {
return null;
}
if (endIndex - startIndex <= 0) {
final int noOfItems = endIndex - startIndex;
if (noOfItems <= 0) {
return EMPTY;
}
final StringBuilder stringBuilder = new StringBuilder();
for (int i = startIndex; i < endIndex; i++) {
final StringBuilder stringBuilder = new StringBuilder(noOfItems * 8);
stringBuilder.append(array[startIndex]);
for (int i = startIndex + 1; i < endIndex; i++) {
stringBuilder
.append(array[i])
.append(delimiter);
.append(delimiter)
.append(array[i]);
}
return stringBuilder.substring(0, stringBuilder.length() - 1);
return stringBuilder.toString();
}

/**
Expand Down Expand Up @@ -4232,16 +4242,18 @@ public static String join(final int[] array, final char delimiter, final int sta
if (array == null) {
return null;
}
if (endIndex - startIndex <= 0) {
final int noOfItems = endIndex - startIndex;
if (noOfItems <= 0) {
return EMPTY;
}
final StringBuilder stringBuilder = new StringBuilder();
for (int i = startIndex; i < endIndex; i++) {
final StringBuilder stringBuilder = new StringBuilder(noOfItems * 4);
stringBuilder.append(array[startIndex]);
for (int i = startIndex + 1; i < endIndex; i++) {
stringBuilder
.append(array[i])
.append(delimiter);
.append(delimiter)
.append(array[i]);
}
return stringBuilder.substring(0, stringBuilder.length() - 1);
return stringBuilder.toString();
}

/**
Expand Down Expand Up @@ -4470,16 +4482,18 @@ public static String join(final long[] array, final char delimiter, final int st
if (array == null) {
return null;
}
if (endIndex - startIndex <= 0) {
final int noOfItems = endIndex - startIndex;
if (noOfItems <= 0) {
return EMPTY;
}
final StringBuilder stringBuilder = new StringBuilder();
for (int i = startIndex; i < endIndex; i++) {
final StringBuilder stringBuilder = new StringBuilder(noOfItems * 10);
stringBuilder.append(array[startIndex]);
for (int i = startIndex + 1; i < endIndex; i++) {
stringBuilder
.append(array[i])
.append(delimiter);
.append(delimiter)
.append(array[i]);
}
return stringBuilder.substring(0, stringBuilder.length() - 1);
return stringBuilder.toString();
}

/**
Expand Down Expand Up @@ -4664,16 +4678,18 @@ public static String join(final short[] array, final char delimiter, final int s
if (array == null) {
return null;
}
if (endIndex - startIndex <= 0) {
final int noOfItems = endIndex - startIndex;
if (noOfItems <= 0) {
return EMPTY;
}
final StringBuilder stringBuilder = new StringBuilder();
for (int i = startIndex; i < endIndex; i++) {
final StringBuilder stringBuilder = new StringBuilder(noOfItems * 6);
stringBuilder.append(array[startIndex]);
for (int i = startIndex + 1; i < endIndex; i++) {
stringBuilder
.append(array[i])
.append(delimiter);
.append(delimiter)
.append(array[i]);
}
return stringBuilder.substring(0, stringBuilder.length() - 1);
return stringBuilder.toString();
}

/**
Expand Down
174 changes: 174 additions & 0 deletions src/test/java/org/apache/commons/lang3/StringUtilsJoinBenchmark.java
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Original file line number Diff line number Diff line change
@@ -0,0 +1,174 @@
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.lang3;

import java.util.Random;
import java.util.concurrent.TimeUnit;
import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Fork;
import org.openjdk.jmh.annotations.Measurement;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import org.openjdk.jmh.annotations.Param;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.Setup;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.annotations.Warmup;

public class StringUtilsJoinBenchmark {

@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@State(Scope.Thread)
@Fork(1)
@Warmup(iterations = 2, time = 1)
@Measurement(iterations = 3, time = 1)
public static class IntArrayBenchmark {

@Param({ "10", "100", "1000", "10000" })
private int size;

private int[] intArray;

@Setup
public void setup() {
intArray = new int[size];
Random random = new Random(235);
for (int i = 0; i < size; i++) {
intArray[i] = random.nextInt(10000);
}
}

@Benchmark
public String testJoinIntWithoutInitCapacity() {
return StringUtilsWithoutInitCapacity.join(intArray, ',', 0, intArray.length);
}

@Benchmark
public String testJoinIntWithInitCapacity() {
return StringUtilsWithInitCapacity.join(intArray, ',', 0, intArray.length);
}
}

@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@State(Scope.Thread)
@Fork(1)
@Warmup(iterations = 2, time = 1)
@Measurement(iterations = 3, time = 1)
public static class BooleanArrayBenchmark {

private boolean[] boolArray;

@Setup
public void setup() {
boolArray = new boolean[10000];
for (int i = 0; i < boolArray.length; i++) {
boolArray[i] = (i % 2 == 0);
}
}

@Benchmark
public String testJoinBooleanInitArrayLength() {
return StringUtilsWithoutInitCapacity.join(boolArray, ',', 0, 10);
}

@Benchmark
public String testJoinBooleanInitNoOfItems() {
return StringUtilsWithInitCapacity.join(boolArray, ',', 0, 10);
}
}

public static class StringUtilsWithInitCapacity {

public static final String EMPTY = "";

public static String join(final boolean[] array, final char delimiter, final int startIndex, final int endIndex) {
if (array == null) {
return null;
}
final int noOfItems = endIndex - startIndex;
if (noOfItems <= 0) {
return EMPTY;
}
final StringBuilder stringBuilder = new StringBuilder(noOfItems * 5 + noOfItems - 1);
stringBuilder.append(array[startIndex]);
for (int i = startIndex + 1; i < endIndex; i++) {
stringBuilder
.append(delimiter)
.append(array[i]);
}
return stringBuilder.toString();
}

public static String join(final int[] array, final char delimiter, final int startIndex, final int endIndex) {
if (array == null) {
return null;
}
final int noOfItems = endIndex - startIndex;
if (noOfItems <= 0) {
return EMPTY;
}
final StringBuilder stringBuilder = new StringBuilder(noOfItems * 4);
stringBuilder.append(array[startIndex]);
for (int i = startIndex + 1; i < endIndex; i++) {
stringBuilder
.append(delimiter)
.append(array[i]);
}
return stringBuilder.toString();
}
}

public static class StringUtilsWithoutInitCapacity {

public static final String EMPTY = "";

public static String join(final boolean[] array, final char delimiter, final int startIndex, final int endIndex) {
if (array == null) {
return null;
}
if (endIndex - startIndex <= 0) {
return EMPTY;
}
final StringBuilder stringBuilder = new StringBuilder(array.length * 5 + array.length - 1);
for (int i = startIndex; i < endIndex; i++) {
stringBuilder
.append(array[i])
.append(delimiter);
}
return stringBuilder.substring(0, stringBuilder.length() - 1);
}

public static String join(final int[] array, final char delimiter, final int startIndex, final int endIndex) {
if (array == null) {
return null;
}
if (endIndex - startIndex <= 0) {
return EMPTY;
}
final StringBuilder stringBuilder = new StringBuilder();
for (int i = startIndex; i < endIndex; i++) {
stringBuilder
.append(array[i])
.append(delimiter);
}
return stringBuilder.substring(0, stringBuilder.length() - 1);
}
}
}