Java Data Size Formatter (kB, MB, GB, ...)

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/*
 * DataSizeFormatter 2018-01-01
 * 
 * This is free and unencumbered software released into the public domain.
 * 
 * Anyone is free to copy, modify, publish, use, compile, sell, or distribute
 * this software, either in source code form or as a compiled binary, for any
 * purpose, commercial or non-commercial, and by any means.
 * 
 * In jurisdictions that recognize copyright laws, the author or authors of this
 * software dedicate any and all copyright interest in the software to the
 * public domain. We make this dedication for the benefit of the public at large
 * and to the detriment of our heirs and successors. We intend this dedication
 * to be an overt act of relinquishment in perpetuity of all present and future
 * rights to this software under copyright law.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 * 
 * For more information, please refer to <http://unlicense.org/>
 */

/**
 * A formatter for data sizes, e.g. formats the number 213425535 to "204 MiB".
 * If you are not sure which of the three formats to use, then use the newest
 * and clearly defined formatNeo(...).
 */
public class DataSizeFormatter {

	private static final long K = 1000;
	private static final long M = K * K;
	private static final long G = M * K;
	private static final long T = G * K;
	private static final long P = T * K;
	private static final long E = P * K;
	private static final long Z = E * K;
	private static final long Y = Z * K;
	private static final long[] METRIC_INTERVAL_LIST = { 1, K, M, G, T, P, E, Z, Y };
	private static final String[] METRIC_UNIT_LIST = { "B", "kB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB" };

	private static final long Ki = 1024;
	private static final long Mi = Ki * Ki;
	private static final long Gi = Mi * Ki;
	private static final long Ti = Gi * Ki;
	private static final long Pi = Ti * Ki;
	private static final long Ei = Pi * Ki;
	private static final long Zi = Ei * Ki;
	private static final long Yi = Zi * Ki;
	private static final long[] NEO_INTERVAL_LIST = { 1, Ki, Mi, Gi, Ti, Pi, Ei, Zi, Yi };
	private static final String[] NEO_UNIT_LIST = { "B", "KiB", "MiB", "GiB", "TiB", "PiB", "EiB", "ZiB", "YiB" };

	/**
	 * Formatting with neo unit symbols KiB, MiB, and so on, which are clearly
	 * defined to use 1024 as conversion factor for different units.
	 */
	public static String formatNeo(long size) {
		return format(size, NEO_INTERVAL_LIST, NEO_UNIT_LIST);
	}

	/**
	 * Correct metric formatting with 1000 as conversion factor and metric units kB,
	 * MB, and so on, which is however too easy to confuse with classic formatting,
	 * which uses the same unit symbols. Many storage device producers use this
	 * metric format to make their devices look bigger.
	 */
	public static String formatMetric(long size) {
		return format(size, METRIC_INTERVAL_LIST, METRIC_UNIT_LIST);
	}

	/**
	 * Classic, but outdated fashion to format with seemingly metric units kB, MB,
	 * and so on, but with an conversion rate of 1024 instead of the metric 1000.
	 */
	public static String formatClassic(long size) {
		return format(size, NEO_INTERVAL_LIST, METRIC_UNIT_LIST);
	}

	private static String format(long size, long[] intervalList, String[] unitList) {
		String signStr;
		if (size < 0) {
			size = -size;
			signStr = "-";
		} else {
			signStr = "";
		}

		int interval = getInterval(size, intervalList);
		double converted = ((double) size) / intervalList[interval];

		String unitStr = unitList[interval];

		String convertedStr = toRoundedString(converted);

		return signStr + convertedStr + " " + unitStr;
	}

	private static int getInterval(long size, long[] intervals) {
		if (size < intervals[1]) {
			return 0;
		} else if (size < intervals[2]) {
			return 1;
		} else if (size < intervals[3]) {
			return 2;
		} else if (size < intervals[4]) {
			return 3;
		} else if (size < intervals[5]) {
			return 4;
		} else if (size < intervals[6]) {
			return 5;
		} else if (size < intervals[7]) {
			return 6;
		} else if (size < intervals[8]) {
			return 7;
		} else {
			return 8;
		}
	}

	private static String toRoundedString(double converted) {
		String convertedStr;

		if (converted < 10) {
			convertedStr = Double.toString(Math.round(converted * 10.0D) / 10.0D);
		} else {
			convertedStr = Long.toString(Math.round(converted));
		}

		return convertedStr;
	}
}