equals（）vs compareTo（）in Comparator / able（Theoretical） [英] equals() vs compareTo() in Comparator/able (Theoretical)

问题描述

我不懂得Javadoc：

 类C的自然排序被认为与equals相一致if和只有当
（e1.compareTo（（Object）e2）== 0）具有与e1.equals（（Object）e2）相同的布尔值，对于
每个类C的e1和e2。
  

为什么会这样？

e1.equals（e2）= true应该总是暗示e1.compareTo（e2）== 0，但我不明白为什么相反应该是真的。比较不平等！ 2个相等的对象应该与零相比较，但是如果排序的标准与它们的情况不相关，则2个不同的对象应该能够比较为0。我的意思是，有不同的对象等于不正确，但不同的对象与0比较为什么不？

编辑：后来说，对于一些兼容性问题，因此问题

解决方案

Javadoc不是说它是有一个与equals不一致的比较。

当你得到选择时，通常最好使比较与equals相一致，使得给定的A和B，A小于，等于或大于B，但不是以这种方式工作。

这是重要的，你记录下来，但调用者可能会非常困惑的排序，这是意想不到的等于。

I don,t understand Javadoc:

The natural ordering for a class C is said to be consistent with equals if and only if
  (e1.compareTo((Object)e2) == 0) has the same boolean value as e1.equals((Object)e2) for
  every e1 and e2 of class C.

Why should be that way?

I understand that e1.equals(e2)=true should always imply e1.compareTo(e2)==0, but I cannot understand why the opposite should be true. Compareness is not equalness! 2 equal objects should be compared to zero, but 2 differents ones should be able to compareTo 0 if the criteria for sorting is not relevant in their case. I mean, having different objects equaling is not correct, but different objects with a 0 comparation why not?

EDIT: Later it says that consistency is strong recommended, for some compatibility issues, and hence the question

解决方案

That Javadoc isn't saying it's wrong to have a comparison which isn't consistent with equals. It's just defining the terminology for a comparison being consistent with equals.

When you get the choice it's generally nice to make a comparison consistent with equals, such that given A and B, A is either less than, equal to or greater than B - but it doesn't have to work that way.

It is important that you document this though - callers could get very confused with an ordering which is unexpectedly not consistent with equals.

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