CODEWITHSUNDEEP
java
pred1212
pred1212

Reputation: 3

Try-with-resource / Closable-Autoclosable

I’m trying to understand Try-with-resource. After reading few articles, I understand that each class who implement or extend closable/auto-closable can benefit from the close() method which is called to close the object.

Now in practice I have this code:

try (FileInputStream inputStream = new FileInputStream(instructionFile);
     Scanner sc = new Scanner(inputStream, "UTF-8")) {
    while (sc.hasNextLine()) {
        String startingPosition = sc.nextLine();
        String instructions = sc.nextLine();
        // Some actions
    }
    if (sc.ioException() != null) {
        throw sc.ioException();
    }
} catch (NoSuchElementException e) {
    throw new IncompleteInstructions();
} catch (IOException e) {
    throw e;
}

As you can see, I used FileInputStream and Scanner classes, I was expecting to see both of those class implements or extends Closable, instead I have the classic method close(), seems to be a wrap of Closable.

My question, who should implement or extend Closable, is it the source of data, like files for FileInputStream class and Readable interface for the Scanner class.

Thanks you !

Upvotes: 0

Views: 2646

Answers (2)

Lucas Campos
Lucas Campos

Reputation: 1920

Both of your classes implements Closeable which extends AutoCloseable.

Reading their javadoc helps but, in the end, their close method will be automatically called by the try-with-resources.

AutoCloseable javadoc:

An object that may hold resources (such as file or socket handles) until it is closed. The close() method of an AutoCloseable object is called automatically when exiting a try-with-resources block for which the object has been declared in the resource specification header. This construction ensures prompt release, avoiding resource exhaustion exceptions and errors that may otherwise occur.

Upvotes: 3

Giorgi Tsiklauri
Giorgi Tsiklauri

Reputation: 11120

FileInputStream extends InputeStream

InputStream and Scanner both implement Closable

Closable extends AutoClosable

So FileInputStream and Scanner instances are AutoClosable and after the instructions in the try block finish the execution, JVM will automatically call .close() method on those resources. As Java docs state,

The try-with-resources statement ensures that each resource is closed at the end of the statement.

Upvotes: 0

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