问题
I just found out that I can compare null with an Object like this,
if(null != Object)
Rather than comparing Object with null, like
Object != null
What may go wrong if use the former approach?
Is that legal? If not then why does compiler accept it?
回答1:
There's one thing wrong about it - readability. If you want to write a clean code, you should care about the way it will be read in the future. It needs to be obvious, what it does and why it does a certain thing. If you place the "Object" to the right of the evaluation, it becomes less apparent what are you really doing. Well at least in my opinion...
回答2:
Both are equivalent, but the null != object is an old practice from languages where it is valid to write if (object = null) and accidentally
assign null to the object. It is a guard to stop this accident from happening.
回答3:
Most people say Object != null because it is what they are used to and so it is easier to read.
The best argument I've heard for null != object is to avoid bad expressions. e.g. to pickup a typo in if (var == 1)
if (var = 1) // this is valid C
if (1 = var) // this is not valid C
回答4:
It's just a matter of readability. If you can read your code out loud and it makes sense it is easier to understand. The second version is like Yoda-talk.. "null is not the object.." compared the "The object is not null"..
This same goes for giving your variables and methods good names.
A good reference site for writing readable code: http://www.cleancoders.com/
回答5:
It is the same. It is almost like saying if 1 != 2. Does this imply 2 != 1?
回答6:
The != operator behaves just as the test for equality operator == .
Ignoring any side effects in the expressions then (expr1 != expr2) and (expr2 != expr1) are exactly the same.
If Object is a variable (or constant) then (null != Object) is just as valid (although a little bit less readable).
来源：https://stackoverflow.com/questions/10244682/what-is-wrong-in-comparing-a-null-with-an-object-rather-than-an-object-with-a-nu