java入门：文件操作

import java.io.FileInputStream; import java.io.FileOutputStream;import java.io.PrintStream;public class Main {public static void f_useFileIN(String name) {                 try {        System.setIn(new FileInputStream(name));        }         catch (Exception e) {        System.err.println("Error instream!");        }              }public static void f_useFileOUT(String name) {        try {        System.setOut(new PrintStream(new FileOutputStream(name)));        }         catch (Exception e) {        System.err.println("Error outstream!");        }}public static void main(String args[]) {//f_useFileIN("data.in");//f_useFileOUT("data.out");        System.err.println("OK");}}