CODEWITHSUNDEEP
javaexceptionnullpointerexceptionbufferedreader
Saikat
Saikat

Reputation: 16810

Can BufferedReader be closed automatically in Java

I was getting an warning on resource leak (BufferedReader was not closed). I fixed that by putting a close statement before the Return statement and ran the program. But I got an NullPointerException. My question is can it be closed automatically (somehow) when file reading was done. This question looks similar though.

Upvotes: 4

Views: 2676

Answers (2)

AlexR
AlexR

Reputation: 115338

Prior java 7 the general pattern of closable IO resources was like the following:

Resource r = null; // either stream, reader, writer etc
try { 
    r = ... // create resource
    use resource r
} catch(IOException e) {
   // some code
} finally {
    if (r != null) {
         r.close();
    }
}

The resource is used in finally block that guarantees that it will be closed whether the operation is done successfully or failed. null-check is needed to prevent NPE if IOException was thrown while creating the resource.

Java 7 introduced new syntax that creates illusion that the resource is closed "automatically":

try (
    Resource r = // create resource
){ 
    use resource r
} catch(IOException e) {
   // some code
}

finally block is actually added here automatically by compiler.

I hope this answers your question about automatic closing of BufferedReader.

Upvotes: 2

Evgeniy Dorofeev
Evgeniy Dorofeev

Reputation: 136042

You can use try-with-resources Java 7 feature:

try(BufferedReader rdr = new BufferedReader(...)) {
     ...
}

it will be closed automatically when exiting block

http://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html

Upvotes: 9

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