Here you can find the source of getNextId()
private static int getNextId()
//package com.java2s; /*/*from w w w . jav a 2 s . co m*/ * Copyright (c) 2016 The Jupiter Project * * 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. */ import java.util.concurrent.atomic.AtomicInteger; public class Main { private static final int ID_BASE = 1000; private static final int ID_MASK = (1 << 13) - 1; private static final AtomicInteger id = new AtomicInteger(0); private static int getNextId() { // (1000 + 0) ~ (1000 + 8191) return (id.getAndIncrement() & ID_MASK) + ID_BASE; } }