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Input/Output: Exploring java.io >
Siva Nookala - 06 Oct 2016
In general, a stream must be closed when it is no longer needed. Failure to do so can lead to memory leaks and resource starvation.

Beginning with JDK 7, there are two basic ways in which you can close a stream. The first is to explicitly call close() on the stream. This is the traditional approach that has been used since the original release of Java. With this approach, close() is typically called within a finally block.

try
{
// open and access file
}
catch( I/O-exception)
{
// Do some action
}
finally
{
// close the file
}


This general technique is common in code that predates JDK 7. The second approach to closing a stream is to automate the process by using the new try-with-resources statement that was added by JDK 7. The try-withresources statement is an enhanced form of try that has the following form:

try (resource-specification)
{
// use the resource
}


Here, resource-specification is a statement or statements that declares and initializes a resource, such as a file or other stream-related resource. It consists of a variable declaration in which the variable is initialized with a reference to the object being managed. When the try block ends, the resource is automatically released. In the case of a file, this means that the file is automatically closed. Thus, there is no need to call close() explicitly.

Here are three key points about the try-with-resources statement:
  • Resources managed by try-with-resources must be objects of classes that implement AutoCloseable.
  • The resource declared in the try is implicitly final.
  • You can manage more than one resource by separating each declaration by a semicolon.

Also, remember that the scope of the declared resource is limited to the try-with-resources statement.

The principal advantage of try-with-resources is that the resource (in this case, a stream) is closed automatically when the try block ends. Thus, it is not possible to forget to close the stream, for example. The try-with-resources approach also typically results in shorter, clearer, easier-to-maintain source code.

One last point: The examples that use try-withresources must be compiled by a JDK 7 or later. They won’t work with an older compiler. The examples that use the traditional approach can be compiled by older versions of Java.

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