error while using try with resources in Java

Question

I have this method where I am using try with resources of Java SE 7.

private void generateSecretWord(String filename){

        try (FileReader files = new FileReader(filename)){
            Scanner input = new Scanner(files);
            String line = input.nextLine();
            String[] words = line.split(",");
            Collections.shuffle(Arrays.asList(words));
            if (words[0].length()>1){
                secretWord = words[0];
                return;
            }

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        finally {
            if (files!=null) files.close(); 
        }

    }

I get compile error in finally block that files cannot be resolved to a variable I have reference for files in the try with block. why do I get this error and how to fix it?

Thanks

Neidaneidhardt

Answer 1

Taken from the Java Language Spec (14.20.3):

A try-with-resources statement is parameterized with variables (known as resources) that are initialized before execution of the try block and closed automatically, in the reverse order from which they were initialized, after execution of the try block. catch clauses and a finally clause are often unnecessary when resources are closed automatically.

A ResourceSpecification declares one or more local variables with initializer expressions to act as resources for the try statement.

So you do not need to close the Resource anymore. Try-with-resources does it automatically for you and your FileReader will only be available in the try block. Thus you get that compile error.

Shih

does that mean a finally block is not needed or just closing files is not needed – Proboscis

@user2708477 It means that a finally block is not needed to close the Resources. If you need to do other things, which cannot be skipped even if an Exception happens, then you will still need a finally block. But if you just want to make sure that the files will be closed in any case, you don't need one, because that will be done implicitly. – Shih

Answer 2

When you are using try with resources you don't need to explicitly close them. try-with-resources will take care of closing those resources.

Based on try-wtih-resource document

The try-with-resources statement is a try statement that declares one or more resources. A resource is an object that must be closed after the program is finished with it. The try-with-resources statement ensures that each resource is closed at the end of the statement.

Delighted

Answer 3

Since no-one else has mentioned this, if you want to handle it manually you could do something like:

private void generateSecretWord(String filename){
        FileReader files = null;
        try {
            files = new FileReader(filename);
            Scanner input = new Scanner(files);
            String line = input.nextLine();
            String[] words = line.split(",");
            Collections.shuffle(Arrays.asList(words));
            if (words[0].length()>1){
                secretWord = words[0];
                return;
            }

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        finally {
            if (files!=null) 
                files.close(); 
        }

    }

Edh

Answer 4

The code that you are trying to execute is old fashioned code before Java 7 where have to close the resources to avoid memory leaks. But in New Java 7 take it smartly and it is not necessary to close the resources even it is not accessible to finally block.

Petronel

Answer 5

in Pom.xml set java to 1.7 or higher as follows,

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
    <java.version>1.8</java.version>
</properties>

Yance