Can BufferedReader be closed automatically in Java

Question

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.

Answer 1

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

Answer 2

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.