Ternary operator is not a statement

Question

I've the following ternary expression:

((!f.exists()) ? (f.createNewFile() ? printFile() : throw new Exception("Error in creating file")) : printFile());

For one, or more, reason that I don't know idea IDE say to me that it isn't a statement. Why?

Without trying to answer the question, just one observation: Are you sure you want your code to look like this? I would kick myself if I wrote it like this and had to revisit it after a couple of weeks.... — Stephen, Jul 23 '15 at 08:57
Yes for me is more readable and also I use comments in my code — Tinwor, Jul 23 '15 at 08:58
What are you trying to achive with the throw? You know that the ternary operator only works with assignments? — SomeJavaGuy, Jul 23 '15 at 09:01
@KevinEsche the ternary operator does not "only works with assignments". — davmac, Jul 23 '15 at 09:14
Why use `f.exists()` and then `f.createNewFile()` ? - the latter will return false if the file already exists, there's no need to do a separate check first. — davmac, Jul 23 '15 at 09:18

score 2 · Accepted Answer · answered Jul 23 '15 at 09:08

2

this is not valid, you need to return a value

printFile() : throw new Exception("Error in creating file")

try this one

if(f.exists() || f.createNewFile()) {
  printFile();
}else{
  throw new Exception("Error in creating file");
}

answered Jul 23 '15 at 09:08

Matteo Rubini

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I think the error is thrown with `f.createNewFile()` without throwing the custom exception. At least when i enter an invalid path for a file. – SomeJavaGuy Jul 23 '15 at 09:12
i think the proposed code shoud work in a different way, i have not changed functionality. – Matteo Rubini Jul 23 '15 at 09:14
Answer accepted even if it's not exactly compliant with the question – Tinwor Jul 23 '15 at 12:41

score 1 · Answer 2 · edited May 23 '17 at 11:51

1

It looks like you are using it as a statement and not as an assignment

From what SO says it is not possible to do so

Also from another SO Articel, that says you can´t throw an exception in the ternary statement

I think you need to go back to an if-else clause like this:

if (!f.exists()) {
   try {
      f.createNewFile();
      printFile();
   } catch(Exception e ) {
      System.out.println("Error in creating file");
   }
} else {
   printFile();
}

edited May 23 '17 at 11:51

Community

1
1

answered Jul 23 '15 at 09:07

SomeJavaGuy

7,307
2
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2

The links correctly explain the problem. Just your mention of *assignment* is a bit out of place: the elements of a ternary must be **expressions** (throw is not an expression) and the ternary itself must be used as an **expression** (it's used as a statement in the example). BTW, both Eclipse and javac report a **syntax error** on `throw`. – Stephan Herrmann Jul 23 '15 at 09:37

score 0 · Answer 3 · answered Jul 23 '15 at 10:41

The "COND ? Statement : Statement" construct is an expression. It can not be used as a statement. Without assignment it can be used in situation like resolving condition argument in function call or string concatenation.

Func( (COND ? param1 : param2) );
"Hi"+(con?"Miss":"Mr.")+"";

score 0 · Answer 4 · answered Dec 08 '17 at 05:28

The statements in the ternary operator need to be non-void. They need to return something.

Example:

Consider a case, where count variable gets incremented and I am checking for its value and return true or false above certain threshold.
System.out.println((count >10 ? true: false));
As compared to, count >10 ? true: false where compiler will complain that this is not a statement.

Ternary operator is not a statement

4 Answers4