I am used to Java and therefore always think conditions are interpreted from left to right, i.e. there is a vital difference in null != $obj and $obj != nullNow this seems not to be the case with PHP. Can I do something wrong in PHP when I always start with null on the left-hand side? Can I keep my behaviour from Java or do I need to train myself to do something else when dealing with PHP conditions? 
What is the difference (if any) between (null != $object) and ($object != null) when using PHP?
php;object oriented;code quality;conditions
There is no (technical) difference – nor is there in Java to my knowledge.In PHP, do not use either of these. I recommend you always use the strict comparison operators === and !== if possible. You will know when you actually need loose comparison operators.MisunderstandingsI believe you may be confused about a couple of things:short-circuiting operatorsorder of evaluationoperator precedenceI just found that the PHP manual says:  PHP checks each condition in order from left to rightNo,the PHP manual does not say that, it's a comment.PHP does not do that.PHP evaluates the conditions from left to right, but it stops once the result is known: expr1 && expr2If expr1 evaluates to false, expr2 will not be evaluated. This is called short-circuiting and it does not seem to be very well-documented – I couldn't find any other official note on the matter except for the comment in Example #1. It is a well-known feature, though.FallaciesI am used to Java and therefore always think conditions are interpreted from left to right, i.e. there is a vital difference in null != $obj and $obj != nullPHP checks each condition in order from left to right  Ergo: The same best practice can be appliedErgo: nothing – non sequitur. The conclusion does not follow from the premise. Using constant == $variable or $variable == constant is not connected to either of short-circuiting, order of evaluation or operator precedence.Undefined behaviorBoth operands of != are always evaluated. In the case of PHP, the evaluation order (which is irrelevant here) is actually unspecified (as in absent from the documentation).