java随机数生成具体实现代码

本文实例为大家分享了java随机数生成代码，供大家参考，具体内容如下

package com.gonvan.common.utils;
 
import java.util.*;
 

public final class LotteryAliasMethod {
 
  
  private final Random  random;
 
  
  private final int[]   alias;
 
  
  private final double[] probability;
 
  
  public LotteryAliasMethod(List probabilities) {
    this(probabilities, new Random());
  }
 
  
  public LotteryAliasMethod(List probabilities, Random random) {
    
    if (probabilities == null || random == null)
      throw new NullPointerException();
    if (probabilities.size() == 0)
      throw new IllegalArgumentException("Probability vector must be nonempty.");
 
    
    probability = new double[probabilities.size()];
    alias = new int[probabilities.size()];
 
    
    this.random = random;
 
    
    final double average = 1.0 / probabilities.size();
 
    
    probabilities = new ArrayList(probabilities);
 
    
    Deque small = new ArrayDeque();
    Deque large = new ArrayDeque();
 
    
    for (int i = 0; i < probabilities.size(); ++i) {
      
      if (probabilities.get(i) >= average)
 large.add(i);
      else
 small.add(i);
    }
 
    
    while (!small.isEmpty() && !large.isEmpty()) {
      
      int less = small.removeLast();
      int more = large.removeLast();
 
      
      probability[less] = probabilities.get(less) * probabilities.size();
      alias[less] = more;
 
      
      probabilities.set(more, (probabilities.get(more) + probabilities.get(less)) - average);
 
      
      if (probabilities.get(more) >= 1.0 / probabilities.size())
 large.add(more);
      else
 small.add(more);
    }
 
    
    while (!small.isEmpty())
      probability[small.removeLast()] = 1.0;
    while (!large.isEmpty())
      probability[large.removeLast()] = 1.0;
  }
 
  
  public int next() {
    
    int column = random.nextInt(probability.length);
 
    
    boolean coinToss = random.nextDouble() < probability[column];
 
    
    return coinToss ? column : alias[column];
  }
 
}

以上就是本文的全部内容，希望对大家的学习有所帮助。