object null or null object

Question

I heard from somebody that null    object is better than object    null  check  eg    void m1 Object obj        if null    obj      Is this better than object    null   Why          return         Else blah blah     Is there any reasons or this is another myth   Thanks for help

User · Answer

It is Yoda condition writing in different manner

In java

String myString = null;
if (myString.equals("foobar")) { /* ... */ } //Will give u null pointer

yoda condition

String myString = null;
if ("foobar".equals(myString)) { /* ... */ } // will be false

User · Answer

This is not of much value in Java  1 5   except when the type of object is Boolean   In which case  this can still be handy   if  object   null  will not cause compilation failure in Java 1 5  if object is Boolean but would throw a NullPointerException at runtime

User · Answer

Compare with the following code       String pingResult    asd       long s   System nanoTime          if   null    pingResult                 System out println    null    pingResult               long e   System nanoTime          System out println   e - s         long s1   System nanoTime          if   pingResult    null                 System out println    pingResult    null               long e1   System nanoTime          System out println   e1 - s1      Output  After multiple executions    null    pingResult 325737 pingResult    null 47027   Therefore  pingResult    null is the winner

User · Answer

This also closely relates to   if   foo  equals bar       which is convenient if you don t want to deal with NPEs   if  bar  null  amp  amp  bar equals  foo

User · Answer

This trick supposed to prevent v   null kind of typos   But Java allows only boolean expressions as if   conditions so that trick does not make much sense  compiler will find those typos anyway   It is still valuable trick for C C   code though

User · Answer

For the same reason you do it in C  assignment is an expression  so you put the literal on the left so that you can t overwrite it if you accidentally use   instead of

User · Answer

In Java there is no good reason   A couple of other answers have claimed that it s because you can accidentally make it assignment instead of equality   But in Java  you have to have a boolean in an if  so this   if  o   null    will not compile   The only time this could matter in Java is if the variable is boolean   int m1 boolean x        if  x   true      oops  assignment instead of equality

User · Answer

This is probably a habit learned from C  to avoid this sort of typo  single   instead of a double       if  object   null      The convention of putting the constant on the left side of    isn t really useful in Java since Java requires that the expression in an if evaluate to a boolean value  so unless the constant is a boolean  you d get a compilation error either way you put the arguments   and if it is a boolean  you shouldn t be using    anyway

User · Answer

That is for people who prefer to have the constant on the left side  In most cases having the constant on the left side will prevent NullPointerException to be thrown  or having another nullcheck   For example the String method equals does also a null check  Having the constant on the left  will keep you from writing the additional check  Which  in another way is also performed later  Having the null value on the left is just being consistent   like    String b   null    constant  equals b       result to false  b equals  constant        NullPointerException  b    null  amp  amp  b equals  constant        result to false

User · Answer

As others have said  it s a habit learned from C to avoid typos - although even in C I d expect decent compilers at high enough warning levels to give a warning  As Chandru says  comparing against null in Java in this way would only cause problems if you were using a variable of type Boolean  which you re not in the sample code   I d say that s a pretty rare situation  and not one for which it s worth changing the way you write code everywhere else   I wouldn t bother reversing the operands even in this case  if I m thinking clearly enough to consider reversing them  I m sure I can count the equals signs    What hasn t been mentioned is that many people  myself certainly included  find the if  variable    constant  form to be more readable - it s a more natural way of expressing yourself  This is a reason not to blindly copy a convention from C  You should always question practices  as you re doing here    before assuming that what may be useful in one environment is useful in another

User · Answer

Because of its commutative property  the only difference between object    null and null    object  the Yoda version  is of cognitive nature  how the code is read and digested by the reader  I don t know the definitive answer though  but I do know I personally prefer comparing the object I m inspecting to something else  rather than comparing something else to the object I m inspecting  if that makes any sense  Start with the subject  then the value to compare it to   In some other languages this comparison style is more useful   To safe guard against a missing     sign in general though  I think writing null    object is a misguided act of defensive programming  The better way around this particular code is by guaranteeing the behavior with a junit test  Remember  the possible mistake of missing an     is not dependant on the method s input arguments - you are not dependent on the right use of this API by other people - so a junit test is perfect to safe guard against that instead  Anyway you will want to write junit tests to verify the behavior  a missing     naturally falls within scope

[java] object==null or null==object?

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