Java Try Catch Finally blocks without Catch

Question

I'm reviewing some new code. The program has a try and a finally block only. Since the catch block is excluded, how does the try block work if it encounters an exception or anything throwable? Does it just go directly to the finally block?

Whispering

possible duplicate of Difference between try-finally and try-catch – Sumrall

@mP Everyone should be doing code reviews and asking questions from them is how to learn and improve. – Mix

Answer 1

If any of the code in the try block can throw a checked exception, it has to appear in the throws clause of the method signature. If an unchecked exception is thrown, it's bubbled out of the method.

The finally block is always executed, whether an exception is thrown or not.

Gosport

First paragraph is not necessarily true. Try blocks can be nested. Any uncaught exception, unchecked or not, will bubble out of the method. – Ranking

Try blocks can be nested, but I wouldn't recommend it. I don't write code that way. – Gosport

@duffymo: What is meaning of "bubbled out of the method"? – Jubbulpore

@Anand just some slightly non-technical language for "throwing an exception". – Gosport

Great answer, can anyone explain what "bubbled out of the method" means? It's ignored, or passed up the method chain? – Semiconscious

Not ignored; pass up the method chain. – Gosport

I have seen code with try catch after every line where input is getting collected.As almost every line can throws exception but process continues. For example so if registry not found give error message but read config file. Try database Connection so on. and one exception on top of method. It is sort of multi decision Process flow – Cayman

Ugly, unreadable boilerplate code. There are better ways to do such things. – Gosport

BTW (a bit late) the Exception S "bubbled out of the method" is described by the Java Language Specification as "the method completes abruptly with reason S" – Flatten

Answer 2

A small note on try/finally: The finally will always execute unless

• System.exit() is called.
• The JVM crashes.
• The try{} block never ends (e.g. endless loop).

Maineetloire

What about try{..} catch{ throw ..} finally{..}? I think finally will not be executed – Edee

In that case finally will still be called. Only the original exception is lost. – Maineetloire

Finally will also not be executed if you call System.exit() before. – Excited

@jyw That is what I meant by the first item in the list above. – Maineetloire

I have to say, this covers all the bases! – Counterblow

Answer 3

The Java Language Specification⁽¹⁾ describes how try-catch-finally is executed. Having no catch is equivalent to not having a catch able to catch the given Throwable.

• If execution of the try block completes abruptly because of a throw of a value V, then there is a choice:
  • If the run-time type of V is assignable to the parameter of any catch clause of the try statement, then …
    …
  • If the run-time type of V is not assignable to the parameter of any catch clause of the try statement, then the finally block is executed. Then there is a choice:
    • If the finally block completes normally, then the try statement completes abruptly because of a throw of the value V.
    • If the finally block completes abruptly for reason S, then the try statement completes abruptly for reason S (and the throw of value V is discarded and forgotten).

---

(1) Execution of try-catch-finally

Flatten

Answer 4

The inner finally is executed prior to throwing the exception to the outer block.

public class TryCatchFinally {

  public static void main(String[] args) throws Exception {

    try{
        System.out.println('A');
        try{
            System.out.println('B');
            throw new Exception("threw exception in B");
        }
        finally
        {
            System.out.println('X');
        }
        //any code here in the first try block 
        //is unreachable if an exception occurs in the second try block
    }
    catch(Exception e)
    {
        System.out.println('Y');
    }
    finally
    {
        System.out.println('Z');
    }
  }
}

Results in

A
B
X
Y
Z

Maladjustment

Add a "return;" in the first "finally" block, result would print A,B,X,Z and no Y. Would anyone know why? Essentially this added "return" would mask out the Exception thrown? – Doerr

Answer 5

The finally block is always run after the try block ends, whether try ends normally or abnormally due to an exception, er, throwable.

If an exception is thrown by any of the code within the try block, then the current method simply re-throws (or continues to throw) the same exception (after running the finally block).

If the finally block throws an exception / error / throwable, and there is already a pending throwable, it gets ugly. Quite frankly, I forget exactly what happens (so much for my certification years ago). I think both throwables get linked together, but there is some special voodoo you have to do (i.e. - a method call I would have to look up) to get the original problem before the "finally" barfed, er, threw up.

Incidentally, try/finally is a pretty common thing to do for resource management, since java has no destructors.

E.g. -

r = new LeakyThing();
try { useResource( r); }
finally { r.release(); }  // close, destroy, etc

"Finally", one more tip: if you do bother to put in a catch, either catch specific (expected) throwable subclasses, or just catch "Throwable", not "Exception", for a general catch-all error trap. Too many problems, such as reflection goofs, throw "Errors", rather than "Exceptions", and those will slip right by any "catch all" coded as:

catch ( Exception e) ...  // doesn't really catch *all*, eh?

do this instead:

catch ( Throwable t) ...

Uriniferous

See answer by Carlos Heuberger below for the ugly part. – Czechoslovakia

Answer 6

Java versions before version 7 allow for these three combinations of try-catch-finally...

try - catch
try - catch - finally
try - finally

finally block will be always executed no matter of what's going on in the try or/and catch block. so if there is no catch block, the exception won't be handled here.

However, you will still need an exception handler somewhere in your code - unless you want your application to crash completely of course. It depends on the architecture of your application exactly where that handler is.

• Java try block must be followed by either catch or finally block.
• For each try block there can be zero or more catch blocks, but only one finally block.
• The finally block will not be executed if program exits(either by calling System.exit() or by causing a fatal error that causes the process to abort).

Crossbar

"before version 7 allow" are you implying that Java 7 and Java 8 do not allow these three combinations? I doubt that's what you mean, but that's what your answer implies. – Orndorff

is the finally block executed if there is a return statement in the try block? – Tessler

@Rahul Yes, finally will be called. Ref : #65535 – Crossbar

@Aaron - new syntax for try-with-resource which automagically calls .close() on anything constructed within parens just after the try keyword. – Uriniferous

@Uriniferous You're right, but the resource has to implement the Autocloseable interface – Eugenieeugenio

Answer 7

how does the try block work if it encounters an exception or anything throwable

The exception is thrown out of the block, just as in any other case where it's not caught.

The finally block is executed regardless of how the try block is exited -- regardless whether there are any catches at all, regardless of whether there is a matching catch.

The catch blocks and the finally are orthogonal parts of the try block. You can have either or both. With Java 7, you'll be able to have neither!

Ranking

Answer 8

Don't you try it with that program? It'll goto finally block and executing the finally block, but, the exception won't be handled. But, that exception can be overruled in the finally block!

Plague

Answer 9

The finally block is executed after the try block completes. If something is thrown inside the try block when it leaves the finally block is executed.

Meek

Answer 10

Regardless of exception thrown or not in try block - finally block will be executed. Exception would not be caught.

Appertain

Answer 11

Inside try block we write codes that can throw an exception. The catch block is where we handle the exception. The finally block is always executed no matter whether exception occurs or not.

Now if we have try-finally block instead of try-catch-finally block then the exception will not be handled and after the try block instead of control going to catch block it will go to finally block. We can use try-finally block when we want to do nothing with the exception.

Inconsiderate