Ternary operator in System.out

Question

I found below sysout in our project and it is always printing 'Not Null'. Even I have initialize the Val variable or not, it is printing 'Not Null'.

Also why it is not printing the "mylog" in front? Can someone explain?

String Val = null;
System.out.println("mylog : " + Val!=null ? "Not Null" :"Is Null");

Answer 1

Use paranthesis:

   System.out.println("mylog : " + (Val!=null ? "Not Null" :"Is Null"));

Otherwise it gets interpreted as:

  whatToCheck = "mylog: " + val
  System.out.println(whatToCheck !=null ? "Not Null" : "Is Null"

which evaluates to something like "mylog: null" or "mylog: abc". And that is always a non-null String.

Answer 2

"mylog : " + Val!=null 

will be evaluated to

"mylog : null"

which is not null.

Parenthesis for the rescue.

Why is null converted to the String "null"? See the JLS - 15.18.1.1 String Conversion:

... If the reference is null, it is converted to the string "null"

Also it's very important to understand that this is happening because of Java operator precedence.