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  * Copyright (C) 2014 Zach Melamed
  * Latest version available online at
  * Licensed 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
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * See the License for the specific language governing permissions and
 * limitations under the License.
package com.tectonica.util;
Utility class for generating random IDs.

Zach Melamed
public class NewId
	private static Random rand = new Random();

returns a so-called Time-UUID, i.e. a UUID that guarantees no conflicts at the following probabilities:
  • 99.9999973% (or 1 - 2.7e-8) if called 1,000,000 times in every millisecond
  • value of (1 - 2.7e-14) if called once in every microsecond
  • either way, UUIDs within different milliseconds have 0% probability of conflicting
The resulting UUID when used in sort retains order of creation
	public static String generate()
		String timePart = Long.toHexString(System.currentTimeMillis());
		// all dates between 2004 and and 2527 are taking up 11 hex digits, so no need in extra left-padding
		String randomPart = boxed(Long.toHexString(.nextLong()), 16, '0');
		return timePart + randomPart;
	private static String boxed(String strint targetLengthchar padChar)
		int padsCount = targetLength - str.length();
		if (padsCount == 0) // i.e. no alterations required
			return str;
		if (padsCount < 0) // i.e. need to shorted the string
			return str.substring(-padsCountstr.length());
		// need to left-pad the string
		final char[] pad = new char[padsCount];
		for (int i = 0; i < pad.lengthi++)
			pad[i] = padChar;
		return (new String(pad)).concat(str);

convenience method for adding prefix to the generated id
	public static String generate(String prefix)
		return prefix + generate();

generates a limited-length key (with limited chances of being globally unique). uses all digits and characters (i.e. not hexadecimal)
	public static String generateLimited(int length)
		return boxed(Long.toString(.nextLong(), 36), length'0');
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