Why does an empty try block with catch Exception compile?

Question

A try block without any code :

try {

} catch (Exception ex) {
    // what Exception it is catching
    ex.printStackTrace();
}

The absence of any code means that throwing an exception is impossible, so why doesn't this give an "unreachable catch block" compile error?

Can you give us some more detail here? How are you compiling this code? Are you working inside an IDE such as Eclipse or IntelliJ? Does this code sit in a `.java` source file? — Tim Biegeleisen, Mar 03 '15 at 05:46
Why *shouldn't* it compile? A totally empty java file compiles too. — Bohemian, Mar 03 '15 at 05:48
why what is the problem?Its just a block and that upto you if you dont want to write code .Compiler checks for the error and you dont have any — singhakash, Mar 03 '15 at 05:48
@TimBiegeleisen Of course it is in a .java file. it is a strange comment to make. What matters is it is a perfectly valid Java code snippet. Did you downvote it for this reason? — fastcodejava, Mar 04 '15 at 23:11
@Beezy How so! `try` block is empty, what `Exception` it can throw? Did you downvote it for this reason? — fastcodejava, Mar 06 '15 at 09:28

score 4 · Answer 1 · answered Mar 03 '15 at 05:52

4

Exception includes RuntimeExceptions, which are unchecked and don't need to be declared, so Exception can always be validly caught.

I think this is an unimportant edge case.

answered Mar 03 '15 at 05:52

Bohemian

412,405
93
575
722

How can `RuntimeException` be thrown from empty block? – fastcodejava Mar 03 '15 at 06:02
1

@fast see duplicate (I just found) for a more complete answer from the legend himself – Bohemian Mar 03 '15 at 06:06

Hristo · Answer 2 · 2015-03-03T05:54:31.337

2

That's valid Java syntax. It's the same as having an empty if-block:

if (condition) {

}

... or defining an empty method:

public void empty() {

}

... or only having comments as part of the body:

try {
  // try body
} catch (Exception e) {
  // catch body
}

All of that is valid syntax, so the compiler is happy. Further, since a blank line / empty body is totally ok, no exceptions will be thrown in the body of the try block during runtime, so the code would execute just fine as well.

edited Mar 03 '15 at 05:54

answered Mar 03 '15 at 05:48

Hristo

45,559
65
163
230

3

I think the point is that technically `Exception` can't be thrown from no code, so there should be a "catching unthrown exception" compile error. – Bohemian Mar 03 '15 at 05:52

score 1 · Answer 3 · answered Mar 03 '15 at 05:53

So I am assuming that your question is what Exception will get caught and the answer is none. The exception would only be caught if while running the code within the try block throws an exception. It will then check to see if that exception was caught (FYI Exception will catch all exceptions), if yes it handles it inside the catch block otherwise it causes an error. Since there is nothing in the try block the exception will never be caught because no exception can ever be thrown.

Why does an empty try block with catch Exception compile?

3 Answers3