java null != object 和 object!=null 有什么区别
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what is the difference between null != object and object!=null
提问by rozer
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?
可能的重复：
“null != object”或“object != null”哪个更好？
为什么在 C# 中经常看到“null != variable”而不是“variable != null”？
' ... != null' 或 'null != ...' 最佳性能？
Please guide me.
what is the difference between null != object and object!=null
same for "".equal("something") and "something".equals("")
请指导我。null != object 和 object!=null 之间有什么区别
"".equal("something") 和 "something".equals("")
which one is good for processing.
哪个适合加工。
回答by Tim Lloyd
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.
前两个是等价的，但“null != object”是语言中的一种旧做法，在这种语言中，编写“if (object = null)”并意外地将 null 分配给对象是有效的。它是阻止这次事故发生的警卫。
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("").
第二个 while 等效项具有额外的优势，即如果“something”为空，您将不会得到空引用异常，而如果您这样做了：something".equals("")，您将不会得到空引用异常。
回答by polygenelubricants
There is absolutely no difference in either semantics or performance.
在语义或性能上绝对没有区别。
The ==in this case is a reference inequality operation; it can never throw NullPointerException.
在==这种情况下是一个参考不等式操作; 它永远不能扔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
!=isfalseif the operand values are bothnullor both refer to the same object or array; otherwise, the result istrue.
JLS 15.21.3 引用相等运算符 == 和 !=
如果相等运算符的操作数都是引用类型或空类型，则该操作是对象相等。
的结果
!=是false如果操作数值都null或都引用同一个对象或数组；否则，结果为true。
Use whatever is most readable. Usually it's something != null.
使用最易读的内容。通常是something != null.
