Why Do "null==a"

These days lots of codes look like following

if (null==a) {

which made me a little bit confused "Why?".
I searched internet and found some clue. (BTW, it is called "Yoda Conditions")

Old style C couldn't prevent you from mistyping "=" instead of "=="

Think about it. If you typed "if (a=null) …" where you really meant "if (a==null) ..", it's hard to find bug in the code since it compiles fine.
By reversing it like "if (null=a) .." will cause obvious compile error and we can catch the problem earlier.

C++ has operator overloading

If operator== was overloaded and it can cause infinite loop since the a::operator== will be called again.
See my other posting under generic programming menu.

Early termination

When we do "if (aVar==null)", aVar will be evaluated unnecessarily. Imagine that if aVar has property of other class object and recursively and so on.. All we want to know is simply whether aVar is null. It's more obvious when we're comparing something with equals() method. Object.equals() method can be overridden anytime and it's not guaranteed to act like we expect. Similarly, lots of codes are like

if ("YES".equalsIgnoreCase(answer)) {

We can guess why. It will easily prevent null pointer exception which can happen by

if (answer.equalsIgnoreCase("YES") {

when answer was null.


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