The AutoCloseable, Closeable, and Flushable Interfaces - Java

The AutoCloseable, Closeable, and Flushable Interfaces

There are three interfaces that are quite important to the stream classes. Two are Closeable and Flushable. They are defined in java.io and were added by JDK 5. The third, AutoCloseable, was added by JDK 7. It is packaged in java.lang.

AutoCloseable provides support for the try-with-resources statement, which automates the process of closing a resource. (See Chapter 13.) Only objects of classes that implement AutoCloseable can be managed by try-with-resources. AutoCloseable is discussed in Chapter 17, but it is reviewed here for convenience. The AutoCloseable interface defines only the close( ) method:

void close( ) throws Exception

This method closes the invoking object, releasing any resources that it may hold. It is called automatically at the end of a try-with-resources statement, thus eliminating the need to explicitly call close( ). Because this interface is implemented by all of the I/O classes that open a stream, all such streams can be automatically closed by a try-with-resources statement. Automatically closing a stream ensures that it is properly closed when it is no longer needed, thus preventing memory leaks and other problems.

The Closeable interface also defines the close( ) method. Objects of a class that implement Closeable can be closed. Beginning with JDK 7, Closeable extends AutoCloseable. Therefore, any class that implements Closeable also implements AutoCloseable.

Objects of a class that implements Flushable can force buffered output to be written to the stream to which the object is attached. It defines the flush( ) method, shown here:

void flush( ) throws IOException

Flushing a stream typically causes buffered output to be physically written to the underlying device. This interface is implemented by all of the I/O classes that write to a stream.