Test String.substring with JDK 1.7.0_6+ and JDK 1.6.38 <PathToJdk6/7>java -Xms128M -Xmx128M teststring.Main 100000 1000000 On my desktop: jdk 1.7.0_11 => 33 seconds / 252 KBytes Memory jdk 1.6.0_38 => 25 milliseconds / 782 KBytes Memory 1000 times faster ! ( Ok! for this stupid test ;-) )

Main.java

package teststring;

import java.util.Random;

public class Main {
	private static long now() {
		return System.currentTimeMillis();
	}

	/**
	 * @param args
	 */
	static final String[] letters = { "a", "b", "c", "d", "e", "f" };

	public static final long usedMemoryInKo() {
		Runtime rt = java.lang.Runtime.getRuntime();
		return (rt.totalMemory() - rt.freeMemory()) / 1024;
	}

	public static final String makeLongString(int len) {
		StringBuilder strBuff = new StringBuilder();
		Random rdInt = new Random();
		int lenTab = letters.length;
		for (int i = 0; i < len; i++) {
			strBuff.append(letters[Math.abs(rdInt.nextInt(lenTab))]);
		}
		return strBuff.toString();
	}

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		int longString = Integer.parseInt(args[0]);
		;
		int nbBoucles = Integer.parseInt(args[1]);
		String strToParse = makeLongString(longString);
		long debSubstring1Index = now();
		for (int i = 0; i < nbBoucles; i++) {
			strToParse.substring(i % longString);
		}
		long finSubstring1Index = now();
		long debSubstring2Index = now();
		for (int i = 0; i < nbBoucles; i++) {
			strToParse.substring(i % longString, longString);
		}

		System.out.println("test String.substring(beginIndex) with java "
				+ System.getProperty("java.version") + " takes "
				+ (finSubstring1Index - debSubstring1Index) + " ms");
		System.out
				.println("test String.substring(beginIndex,endIndex) with java "
						+ System.getProperty("java.version")
						+ " takes "
						+ (now() - debSubstring2Index) + " ms");
		System.gc();
		try {
			Thread.sleep(1000);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		System.out.println("Used memory => " + usedMemoryInKo() + "Ko");
	}

}