StringJoiner vs StringBuffer vs Collectors.Joining() Performance Test

In this article we are sharing the program to identify which is the best performance provider out of StringJoiner, StringBuffer, StringBuilder and Collectors.joining() while joining/appending String.

import java.util.ArrayList;
import java.util.List;
import java.util.StringJoiner;
import java.util.stream.Collectors;
public class PerformanceTest {
	public static void main(String[] args) {
		List<String> l = new ArrayList<>();
		for(int i=0;i<1000;i++) {
			l.add("12345"+i);
		}
		long start = System.currentTimeMillis();
		usingStringJoiner(l);
		long middle = System.currentTimeMillis();
		System.out.println("Time taken by StringJoiner : "+(middle - start));
		usingStringBuffer(l);
		long end = System.currentTimeMillis();
		System.out.println("Time taken by StringBuffer : "+(end-middle));
		usingCollectors(l);
		long end1 = System.currentTimeMillis();
		System.out.println("Time taken by Collectors.joining() : "+(end1 - end));
		usingStringBuilder(l);
		System.out.println("Time taken by StringBuilder : "+(System.currentTimeMillis() - end1));
	}
	
	private static void usingStringJoiner(List<String> list) {
		StringJoiner sj = new StringJoiner("|");
		list.stream().filter(code -> code != null).forEach(code -> sj.add(code));
		String s = sj.toString();
		System.out.println(s);
	}
	
	private static void usingStringBuffer(List<String> list) {
		StringBuffer buf = new StringBuffer();
		list.stream().forEach(code -> buf.append(code).append("|"));
		String output = buf.toString();
		if (output.endsWith("|")) {
			output = output.substring(0, output.length() - 1);
		}
		System.out.println(output);
	}
	
	private static void usingCollectors(List<String> list) {
		String str = list.stream().collect(Collectors.joining("|"));
		System.out.println(str);
	}
	
	private static void usingStringBuilder(List<String> list) {
		StringBuilder builder = new StringBuilder();
		list.stream().forEach(code -> builder.append(code).append("|"));
		String output = builder.toString();
		if (output.endsWith("|")) {
			output = output.substring(0, output.length() - 1);
		}
		System.out.println(output);
	}
}

Time taken by StringJoiner : 49
Time taken by StringBuffer : 2
Time taken by Collectors.joining() : 4
Time taken by StringBuilder : 3

If you observe the above statistics of StringJoiner and Collectors.joining(), StringJoiners are taking 49 milliseconds to complete the task where Collectors.joining() is taking only 4 milliseconds which is 45 milliseconds lesser. Here one point I would like to bring to your notice is, StringJoiner is used in the implementation of joining() in Collections. But, when I use StringJoiner externally, it is taking more time than how joining() performing.

public static Collector<CharSequence, ?, String> joining(
CharSequence delimiter, CharSequence prefix, CharSequence suffix) {
    return new CollectorImpl<>(
            () -> new StringJoiner(delimiter, prefix, suffix),
            StringJoiner::add, StringJoiner::merge,
            StringJoiner::toString, CH_NOID);
}

StringJoiner internally uses StringBuilder to store value.

/*
 * StringBuilder value -- at any time, the characters constructed from the
 * prefix, the added element separated by the delimiter, but without the
 * suffix, so that we can more easily add elements without having to jigger
 * the suffix each time.
 */
private StringBuilder value;

/* preparing StringBuiler object in StringJoiner */
private StringBuilder prepareBuilder() {
  if (value != null) {
    value.append(delimiter);
  } else {
    value = new StringBuilder().append(prefix);
  }
  return value;
}

StringBuilder has been used across all the methods of StringJoiner to perform various operations. There is one more option of using StringUtils.join() method to perform similar operation. I would like to suggest to use StringBuffer than StringUtils because it internally uses the StringBuffer only to store value.

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