累加器抽象数据类型

叁歲伎倆 2021-07-25 02:17 357阅读 0赞

**一 累加器抽象数据类型API**

<table> 
 <tbody> 
  <tr> 
   <td colspan="2"> <p>public class Accumulator</p> </td> 
  </tr> 
  <tr> 
   <td> <p>Accumulator()</p> </td> 
   <td> <p>创建一个累加器</p> </td> 
  </tr> 
  <tr> 
   <td> <p>public void addDataValue(double x)</p> </td> 
   <td> <p>添加一个新的数据值</p> </td> 
  </tr> 
  <tr> 
   <td> <p>public double mean()</p> </td> 
   <td> <p>所有数据的平均值</p> </td> 
  </tr> 
  <tr> 
   <td> <p>public String toString()</p> </td> 
   <td> <p>对象的字符串表示</p> </td> 
  </tr> 
 </tbody> 
</table>

**二 典型用例**

package MyAccumulator;
    
    import common.Accumulator;
    import common.StdOut;
    import common.StdRandom;
    
    /**
    * Copyright (C), 2020-2020, XXX有限公司
    * FileName: MyAccumulator
    * Author:   cakin
    * Date:     2020/1/11
    * Description: 累加器测试
    */
    public class MyAccumulator {
        public static void main( String[] args ) {
            int T = Integer.parseInt(args[0]);
            Accumulator a = new Accumulator();
            for(int t = 0;t<T;t++){
                a.addDataValue(StdRandom.uniform());
            }
            StdOut.println(a);
        }
    }

**三 测试结果**

F:\Algorithm\target\classes>java MyAccumulator.MyAccumulator 1000
    n = 1000, mean = 0.501307867820307, stddev = 0.2897746380529854

**四 数据类型的实现**

package common;
    
    public class Accumulator {
        private int n = 0;          // number of data values
        private double sum = 0.0;   // sample variance * (n-1)
        private double mu = 0.0;    // sample mean
    
        public Accumulator() {
        }
    
        public void addDataValue(double x) {
            n++;
            double delta = x - mu;
            mu  += delta / n;
            sum += (double) (n - 1) / n * delta * delta;
        }
    
        public double mean() {
            return mu;
        }
    
        public double var() {
            if (n <= 1) return Double.NaN;
            return sum / (n - 1);
        }
    
        public double stddev() {
            return Math.sqrt(this.var());
        }
    
        public int count() {
            return n;
        }
    
        public String toString() {
            return "n = " + n + ", mean = " + mean() + ", stddev = " + stddev();
        }
    }

**五 参考代码**

[https://gitee.com/cakin24/Algorithm][https_gitee.com_cakin24_Algorithm]

[https_gitee.com_cakin24_Algorithm]: https://gitee.com/cakin24/Algorithm