what is the difference between null != object and object!=null

Question

Possible Duplicates:
which way is better “null != object” or “ object != null”?
Why does one often see “null != variable” instead of “variable != null” in C#?
‘ … != null’ or ‘null != …’ best performance?

Please guide me. what is the difference between null != object and object!=null
same for "".equal("something") and "something".equals("")

which one is good for processing.

Yoda would use the first version of each, other than that, no difference. The second one however, if the first string was null you would have a party in the error log... — Nick Craver, May 30 '10 at 11:55
Duplicate: http://stackoverflow.com/questions/271561/why-does-one-often-see-null-variable-instead-of-variable-null-in-c — Martijn Courteaux, May 30 '10 at 12:01
Duplicate: http://stackoverflow.com/questions/1957836/which-way-is-better-null-object-or-object-null-closed — Martijn Courteaux, May 30 '10 at 12:02
Weird grammatics "Yoda Conditions" http://stackoverflow.com/questions/2349378?tab=votes&page=1#tab-top — stacker, May 30 '10 at 14:05

score 29 · Answer 1 · answered May 30 '10 at 11:55

29

The first two 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.

The second whilst equivalent has the added advantage that if "something" is null you will not get a null reference exception whereas you would if you did: something".equals("").

answered May 30 '10 at 11:55

Tim Lloyd

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Speed me for several seconds. ;) – Artem Barger May 30 '10 at 11:56
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"null != object" also helps the reader parse the condition, because more often than not the "object" part is a more complex expression. – rsp May 30 '10 at 12:35

score 6 · Answer 2 · edited Jun 20 '20 at 09:12

There is absolutely no difference in either semantics or performance.

The == in this case is a reference inequality operation; it can never throw NullPointerException.

JLS 15.21.3 Reference Equality Operators == and !=

If the operands of an equality operator are both of either reference type or the null type, then the operation is object equality.

The result of != is false if the operand values are both null or both refer to the same object or array; otherwise, the result is true.

Use whatever is most readable. Usually it's something != null.

what is the difference between null != object and object!=null

2 Answers2

JLS 15.21.3 Reference Equality Operators == and !=

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