import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
public class MainClass {
public static void main(String[] Args) {
String filepath = "C:/myFile.txt";
File aFile = new File(filepath);
FileOutputStream outputFile = null;
if (aFile.isFile()) {
File newFile = aFile;
do {
String name = newFile.getName();
int period = name.indexOf('.');
newFile = new File(newFile.getParent(), name.substring(0, period) + "_old"
+ name.substring(period));
} while (newFile.exists());
aFile.renameTo(newFile);
}
try {
outputFile = new FileOutputStream(aFile);
System.out.println("myFile.txt output stream created");
} catch (FileNotFoundException e) {
e.printStackTrace(System.err);
}
}
}