java中的可释放资源定义，类似c#中的using

public static class FileDuplicator implements AutoCloseable
{
Scanner in = null;
PrintWriter out = null;

public FileDuplicator(String sourceFile, String destFile) {
try {
in = new Scanner(new FileInputStream(sourceFile));
out = new PrintWriter(destFile);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}

public void copy()
{
while(in.hasNext())
{
out.println(in.next().toUpperCase());
}
out.flush();
in.close();
in = null;
out.close();
out = null;
}

@Override
public void close() throws Exception {
if(in != null)
in.close();
if(out != null)
out.close();
}
}

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.text.DecimalFormat;
import java.util.ArrayList;
import java.util.EventListener;
import java.util.List;
import java.util.Scanner;

public class Test {

public static void main(String[] args) throws FileNotFoundException
{
try (FileDuplicator fd = new FileDuplicator("f:\\test.txt", "f:\\test2.txt"))
{
fd.copy();
} catch (Exception e) {
e.printStackTrace();
}

try(Scanner in = new Scanner(new FileInputStream("f:\\test.txt"));)
{

}

System.out.println("end");
}