4 ms·

>being cast to 'null' curing concatenation What does this mean?

• tantalor 10y ago
  "" + null is "null"
  • ams6110 10y ago
    You're kidding, surely? Java really does that? "" + null should be null (or throw an exception). Null is null and nothing else.
    • deleted 10y ago
      [deleted]
    • fgonzag 10y ago
      I think it should be an exception as those types can not be concatenated. But still , "" + null being "null" is just plain crazy. I could see "" + null == "" (as you are concatenating nothing to the string), or "" + null == null as you are concatenating a string to null, but "null" is bonkers.
      • tantalor 10y ago
        This is why I shrug when people complain about JavaScript casting weirdnesses
    • LgWoodenBadger 10y ago
      The + operator in this case is compiled to call String.valueOf() which returns "null" when given null.
    • tantalor 10y ago
      Not kidding. http://docs.oracle.com/javase/6/docs/api/java/lang/String.html#valueOf%28java.lang.Object%29 http://docs.oracle.com/javase/6/docs/api/java/lang/String.ht... http://stackoverflow.com/questions/4260723/concatenating-null-strings-in-java http://stackoverflow.com/questions/4260723/concatenating-nul...
    • LgWoodenBadger 10y ago
      Nobody writes "" + null. They write "" + myVariableRef. And myVariableRef is null. As I posted earlier, the code is compiled to "" + String.valueOf(myVariableRef). Since the empty String is a valid String, and Strinfg.valueOf() also returns a String, what other behavior would you ever imagine being sane or possible?
      • abritinthebay 10y ago
        An empty string of it HAS to be a string would make infinitely more sense. However a type error wouldn't toady on a strongly typed language
      • avz 10y ago
        > Since the empty String is a valid String, and Strinfg.valueOf() also returns a String, what other behavior would you ever imagine being sane or possible? IMHO, String.valueOf() throwing NPE upon encountering a null reference would be both sane and possible. Unfortunately, it does indeed appear that it returns "null" instead [1]. [1] https://docs.oracle.com/javase/7/docs/api/java/lang/String.html#valueOf(java.lang.Object) https://docs.oracle.com/javase/7/docs/api/java/lang/String.h...
        • samuellb 10y ago
          On the other hand, it's quite convenient to not have to do null checks in debug messages. Compare: log.trace("doStuff(" + obj1 + ", " + obj2 + ")"); to this: log.trace("doStuff(" + (obj1 != null ? obj1 : "null") + ", " + (obj2 != null ? obj2 : "null") + ")"); The second one is IMHO quite hard to read, even in this short example (and code readability is important when you do code reviews)
          • tomtomtom777 10y ago
            That is why you should use string formatting instead of concatenation. For string formatting, rendering "null" (or "") makes sense; for coercion not.
  • landryraccoon 10y ago
    Aren't you glad Java doesn't allow operator overloading, so this sort of mischief is impossible? /s
  • deleted 10y ago
    [deleted]
• carlio 10y ago
  Should have been "during" but I cannot edit my comment so I suppose that typo will live in prosperity.
  • woliveirajr 10y ago
    Posterity?
    • carlio 10y ago
      That's the joke