import java.io.*;
import java.util.*;

public class FileTest
// useage:  java FileTest a-token
// a-token will be written to the end of oldfile.txt
{
   public static void main(String[] args) throws FileNotFoundException
   {
      File oldFile = new File("oldfile.txt");
      File newFile = new File("newfile.txt");
      PrintStream ps = new PrintStream(newFile);  // FileNotFoundException
      Scanner scanOld = null;
      System.out.println("Contents of oldfile.txt before -----------------------");
      if (oldFile.exists())
      {
         scanOld = new Scanner(oldFile);       // FileNotfoundException
         while (scanOld.hasNext())
         {
            String s = scanOld.nextLine();     // could combine these 2 lines
            ps.println(s);                     //    except for next trace line
            System.out.println(s);             // to trace
         }
      }
      if (args.length > 0)
         ps.println(args[0]); // use command line for text to add
      if (scanOld != null) // avoid null pointer exception first run
         scanOld.close();  // must close this connection -- before you can delete the old
      System.out.println("\n" + oldFile.delete());   // true if it worked
                                                     // Can't rename over an existing file
      // System.out.println(oldFile.getName());  tried this to make sure File object is still in RAM
      // even though the disk file has been deleted
      ps.close();  // can't rename newFile without this disconnection
      System.out.println(newFile.renameTo(oldFile)); // true if it rename worked
      System.out.println("Contents of oldfile.txt after -----------------------");
      scanOld = new Scanner(oldFile);          // must rename to oldFile's name before this
      while (scanOld.hasNext())                // to trace
         System.out.println(scanOld.nextLine());
   }
}