Java compiler complaining about unreported IOException

Question

I'm trying to write a method that lists all non-hidden files in a directory. However, when I add the condition !Files.isHidden(filePath) my code won't compile, and the compiler returns the following error:

java.lang.RuntimeException: Uncompilable source code - unreported exception 
java.io.IOException; must be caught or declared to be thrown

I tried to catch the IOException, but the compiler still refuses to compile my code. Is there something glaringly obvious that I'm missing? Code is listed below.

try {    
    Files.walk(Paths.get(root)).forEach(filePath -> {
        if (Files.isRegularFile(filePath) && !Files.isHidden(filePath)) {
            System.out.println(filePath);            
        } });
} catch(IOException ex) {    
  ex.printStackTrace(); 
} catch(Exception ex) {   
  ex.printStackTrace(); 
}

*@the compiler still refuses to compile my code"* - with the same error or a different one? — mikej, Aug 16 '15 at 11:35
You may try the approach outlined here: http://stackoverflow.com/questions/31270759/a-better-approach-to-handling-exceptions-in-a-functional-way — Marko Topolnik, Aug 16 '15 at 12:01

Mureinik · Accepted Answer · 2015-08-17T06:35:35.470

6

The lambda expression passed to Iterable#forEach isn't allowed to throw an exception, so you need to handle it there:

Files.walk(Paths.get(root)).forEach(filePath -> {
    try {
        if (Files.isRegularFile(filePath) && !Files.isHidden(filePath)) {
            System.out.println(filePath);
        }
    } catch (IOException e) {
        e.printStackTrace(); // Or something more intelligent
    }
});

edited Aug 17 '15 at 06:35

answered Aug 16 '15 at 11:39

Mureinik

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1

Note that in general lambda expression is *allowed* to throw an exception. It's not allowed in particular functional interface which is used here. – Tagir Valeev Aug 16 '15 at 16:08
1

@TagirValeev I thought that using "The" instead of "A" in my answer conveyed that notion, but upon re-reading it I agree the point was not made clearly enough. I edited the text to clarify that point. Thanks for your feedback! – Mureinik Aug 17 '15 at 06:37
Well probably that's my problem. In my native language there are no articles, so sometimes I just don't notice the additional meaning they add to the sentence. Nevertheless the clarification is good. – Tagir Valeev Aug 17 '15 at 06:40

score 4 · Answer 2 · answered Aug 16 '15 at 11:39

isHiddenFile() throws an IOException, and you're not catching it. Indeed, forEach() takes a Consumer as argument, and Consumer.accept() can't throw any checked exception. So you need to catch the exception inside by the lambda expression passed to forEach():

Files.walk(Paths.get(root)).forEach(filePath -> {
    try {
        if (Files.isRegularFile(filePath) && !Files.isHidden(filePath)) {
            System.out.println(filePath);            
        } 
    }
    catch (IOException e) {
         // do something here
    }
});

Java compiler complaining about unreported IOException

2 Answers2

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