content: /**
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you 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.alibaba.jstorm.utils;
  
  import java.util.ArrayList;
  
  /**
   * Shuffle the range, this class is used in shuffle grouping, it is better than random, which can't make sure of balance.
   *
   * @author yannian
   */
  public class RandomRange {
      private ArrayList<Integer> rr;
      private Integer amt;
  
      public RandomRange(int amt) {
          this.amt = amt;
          this.rr = rotating_random_range(amt);
      }
  
      public Integer nextInt() {
          return this.acquire_random_range_id();
      }
  
      private ArrayList<Integer> rotating_random_range(int amt) {
  
          ArrayList<Integer> range = new ArrayList<>();
          for (int i = 0; i < amt; i++) {
              range.add(i);
          }
  
          ArrayList<Integer> rtn = new ArrayList<>();
          for (int i = 0; i < amt; i++) {
              int index = (int) (Math.random() * range.size());
              rtn.add(range.remove(index));
          }
  
          return rtn;
      }
  
      private synchronized int acquire_random_range_id() {
          int ret = this.rr.remove(0);
          if (this.rr.size() == 0) {
              this.rr.addAll(rotating_random_range(this.amt));
          }
          return ret;
      }
  
      public static void main(String[] args) {
          RandomRange test = new RandomRange(10);
  
          for (int i = 0; i < 10; i++) {
              System.out.println(test.acquire_random_range_id());
          }
      }
  
  }
  