执行检查java.lang.Double的相等方法 [英] Performant way to check java.lang.Double for equality

问题描述

我理解

  double a = 0.00023d; 
 double b = 0.00029d; 
 
 boolean eq =（a == b）; 
  

很慢。

m使用

  double epsilon = 0.00000001d; 
 eq = Math.abs（a-b） epsilon; 
  

---

问题是 Infinitest 表示考试时间太长。

其他信息

是硬编码，因为它是期望值， b 由

  // fyi：current = int，max = int 
 public double getStatus（）
 {
 double值= 0.0; 
 if（current！= 0&& max！= 0）
 value =（（double）current）/ max; 
返回值; 
} 
  

更新


java.lang.Double会这样。

  public boolean equals（Object obj）{
 return（obj instanceof Double）
&& （doubleToLongBits（（（Double）obj）.value）== 
 doubleToLongBits（value））; 
} 
  

因此可以假设这是最佳做法。

解决方案

JUnit有一个方法检查 Double / p>



  Assert.assertEquals（0.00023d，0.00029d，0.0001d）; 
  

请参阅此API文档。

如评论，JUnit实际上最可能比比较手动与给定增量慢。 JUnit首先执行 Double.compare（expected，actual）后跟（如果不等于） Math.abs（expected - actual）< =希望这个答案对于没有意识到JUnit实际上提供了一个不精确的方法的人有用 Double / code>等同测试。

What is the most performant way to check double values for equality.

I understand that

double a = 0.00023d;
double b = 0.00029d;

boolean eq = (a == b);

is slow.

So I'm using

double epsilon = 0.00000001d;
eq = Math.abs(a - b) < epsilon;

---

The problem is that Infinitest is complaning about tests taking too much time. It's not a big deal (1 sec top), but it made me curious.

Additional info

a is hard coded since it's the expected value, b is computed by

  // fyi: current = int, max = int
  public double getStatus()
  {
    double value = 0.0;
    if (current != 0 && max != 0)
      value = ((double) current) / max;
    return value;
  }

Update

java.lang.Double does it that way

public boolean equals(Object obj) {
return (obj instanceof Double)
       && (doubleToLongBits(((Double)obj).value) ==
          doubleToLongBits(value));
}

so one could assume that is the best practice.

解决方案

JUnit has a method of checking a Double for 'equality' with a given delta:

Assert.assertEquals(0.00023d, 0.00029d, 0.0001d);

See this API documentation.

As noted in the comments, JUnit actually most likely is slower than comparing manually with a given delta. JUnit first does a Double.compare(expected, actual) followed (if not equal) by a Math.abs(expected - actual) <= delta.

Hopefully this answer still is useful for people not aware that JUnit actually provides a way for inexact Double equality testing.

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