create GUID - Java java.util

Java examples for java.util:UUID

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Description

create GUID

Demo Code

/*// ww  w  .jav  a 2 s . c om
 * Copyright 2013 JBoss, by Red Hat, Inc
 *
 * 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
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
//package com.java2s;

public class Main {
    private static final char[] chars = "abcdef1234567890".toCharArray();
    private static final Object seedLock = new Object();
    private static final int MAX = Short.MAX_VALUE;
    private static volatile double rSeed = System.currentTimeMillis()
            % Short.MAX_VALUE;
    private static volatile int _a = 1;
    private static volatile int _b = 1000;

    public static String createGUID() {

        final double seed;

        final int q, p;
        synchronized (seedLock) {
            seed = ++rSeed;
            if (++_a == 100000) {
                _a = 1;
            }
            if (--_b == 0) {
                _b = (int) System.currentTimeMillis() % Short.MAX_VALUE;
            }
            q = _a;
            p = _b;
        }

        final long time = System.currentTimeMillis() + q;
        int a = (int) ((time & 0xFFFF) * 73278) + q, x, b = ((int) (time & 0xFFFF) * 33187)
                + p;

        if (b < 0) {
            b = -b;
        } else if (b == 0) {
            b = 2;
        }

        x = (int) seed * a / b;

        final char[] charArray = new char[35];

        for (int i = 0; i < 35; i++) {
            if (i != (charArray.length - 1) && i % 5 == 0) {
                charArray[i] = ':';
                continue;
            }

            x = (a * x + b) % MAX;
            a += time << 16 % MAX;
            b += time << 10 % MAX;

            int idx = x;
            if (idx < 0)
                idx = -idx;

            charArray[i] = chars[idx % chars.length];
        }

        return new String(charArray, 1, charArray.length - 1);
    }
}

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