[SOLVED] implements Closeable or implements AutoCloseable

implements Closeable or implements AutoCloseable

I'm in the process of learning Java and I cannot find any good explanation on the implements Closeable and the implements AutoCloseable interfaces.

When I implemented an interface Closeable, my Eclipse IDE created a method public void close() throws IOException.

I can close the stream using pw.close(); without the interface. But, I cannot understand how I can implement theclose() method using the interface. And, what is the purpose of this interface?

Also I would like to know: how can I check if IOstream was really closed?

I was using the basic code below

import java.io.*;

public class IOtest implements AutoCloseable {

public static void main(String[] args) throws IOException  {

    File file = new File("C:\\test.txt");
    PrintWriter pw = new PrintWriter(file);

    System.out.println("file has been created");

    pw.println("file has been created");

}

@Override
public void close() throws IOException {


}

Solution

In the code you have posted, you don't need to implement AutoCloseable.

You only have to (or should) implement Closeable or AutoCloseable if you are about to implement your own PrintWriter, which handles files or any other resources which needs to be closed.

In your implementation, it is enough to call pw.close(). You should do this in a finally block:

PrintWriter pw = null;
try {
   File file = new File("C:\\test.txt");
   pw = new PrintWriter(file);
} catch (IOException e) {
   System.out.println("bad things happen");
} finally {
   if (pw != null) {
      try {
         pw.close();
      } catch (IOException e) {
      }
   }
}

The code above is Java 6 related. In Java 7 this can be done more elegantly (see this answer).