StringSizeEstimator.java

/*******************************************************************************
 * GenPlay, Einstein Genome Analyzer
 * Copyright (C) 2009, 2014 Albert Einstein College of Medicine
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 * Authors: Julien Lajugie <julien.lajugie@einstein.yu.edu>
 *          Nicolas Fourel <nicolas.fourel@einstein.yu.edu>
 *          Eric Bouhassira <eric.bouhassira@einstein.yu.edu>
 * 
 * Website: <http://genplay.einstein.yu.edu>
 ******************************************************************************/
package edu.yu.einstein.genplay.core.IO.fileSorter;


/**
 * @author Eleftherios Chetzakis
 * 
 */
public final class StringSizeEstimator {

	private static int OBJ_HEADER;
	private static int ARR_HEADER;
	private static int INT_FIELDS = 12;
	private static int OBJ_REF;
	private static int OBJ_OVERHEAD;
	private static boolean IS_64_BIT_JVM;

	/**
	 * Class initializations.
	 */
	static {
		// By default we assume 64 bit JVM
		// (defensive approach since we will get
		// larger estimations in case we are not sure)
		IS_64_BIT_JVM = true;
		// check the system property "sun.arch.data.model"
		// not very safe, as it might not work for all JVM implementations
		// nevertheless the worst thing that might happen is that the JVM is 32bit
		// but we assume its 64bit, so we will be counting a few extra bytes per string object
		// no harm done here since this is just an approximation.
		String arch = System.getProperty("sun.arch.data.model");
		if (arch != null) {
			if (arch.indexOf("32") != -1) {
				// If exists and is 32 bit then we assume a 32bit JVM
				IS_64_BIT_JVM = false;
			}
		}
		// The sizes below are a bit rough as we don't take into account
		// advanced JVM options such as compressed oops
		// however if our calculation is not accurate it'll be a bit over
		// so there is no danger of an out of memory error because of this.
		OBJ_HEADER = IS_64_BIT_JVM ? 16 : 8;
		ARR_HEADER = IS_64_BIT_JVM ? 24 : 12;
		OBJ_REF = IS_64_BIT_JVM ? 8 : 4;
		OBJ_OVERHEAD = OBJ_HEADER + INT_FIELDS + OBJ_REF + ARR_HEADER;

	}

	/**
	 * Estimates the size of a {@link String} object in bytes.
	 * 
	 * @param s The string to estimate memory footprint.
	 * @return The <strong>estimated</strong> size in bytes.
	 */
	public static long estimatedSizeOf(String s) {
		return (s.length() * 2) + OBJ_OVERHEAD;
	}

	/**
	 * Private constructor to prevent instantiation.
	 */
	private StringSizeEstimator() {
	}

}