Java 如何将双精度值设置为“非值”

How do you set a double value to a "non-value"

提问by Ankur

I have two double data elements in an object.

我在一个对象中有两个双数据元素。

Sometimes they are set with a proper value and sometimes not. When the form field from which they values are received is not filled I want to set them to some value that tells me, during the rest of the code that the form fields were left empty.

有时它们设置了适当的值，有时则没有。当接收它们值的表单字段未填充时，我想将它们设置为某个值，在其余代码中，表单字段留空。

I can't set the values to null as that gives an error, is there some way I can make them 'Undefined'.

我无法将值设置为 null，因为这会产生错误，有什么方法可以使它们“未定义”。

PS. Not only am I not sure that this is possible, it might not also make sense. But if there is some best practice for such a situation I would be keen to hear it.

附注。我不仅不确定这是否可行，而且可能也没有意义。但是，如果有针对这种情况的最佳实践，我会很想听听。

采纳答案by Jon Skeet

Two obvious options:

两个明显的选择：

• Use Doubleinstead of double. You can then use null, but you've changed the memory patterns involved substantially.

• Use a "not a number" (NaN) value:

  double d = 5.5;
  System.out.println(Double.isNaN(d)); // false
  d = Double.NaN;
  System.out.println(Double.isNaN(d)); // true
  

  Note that some other operations on "normal" numbers could give you NaN values as well though (0 divided by 0 for example).

• 使用Double代替double。然后您可以使用null，但您已经大大改变了所涉及的内存模式。

• 使用“非数字”(NaN) 值：

  double d = 5.5;
  System.out.println(Double.isNaN(d)); // false
  d = Double.NaN;
  System.out.println(Double.isNaN(d)); // true
  

  请注意，对“正常”数字的其他一些操作也可以为您提供 NaN 值（例如，0 除以 0）。