Null != obj Vs obj != Null

Hey Maris! Long time no see, hope you are well.

cotton.ma at 2007-7-28 19:59:46 >

No difference.

It comes from C/C++, in order to turn typos on the programmer's part from runtime errors (harder to track down) to compile-time errors (easier to track down). If you did if (x = 5) (Note the single =) you could inadvertently assign 5 to x, but the compiler wouldn't let you do if (5 = x) because you can't set the value of the literal 5.

In Java, that's not necessary, because if (x = 5) won't compile.

There are only two cases where something like that matters in Java

if ("something".equals(theStr)) or if ("".equals(theStr))

Since the string literal inside "" is obviously not null, you can't get NullPointerException.

if (true == x)

Booleans are the only type where you can inadvertently assign with if (x = true). Flipping the order gives a compile time error, which is what you'd want. However, this is pointless, since you should never write if (x == true) or if (true == x). You should just write if (x).

As far as if (x == null), the "x == null" order is generally preferred, bcause it looks more natural that the value you're testing comes first. In normal English speech, "If x is null" "If the box is empty" etc.

jverda at 2007-7-28 19:59:46 >