輸入流輸出流打印到文件

藍橋杯真題，

package demo2;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintStream;
import java.math.BigInteger;
 
public class Main8 {
 
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        try {
            PrintStream out = System.out;
            PrintStream ps = new PrintStream(new File("ans.txt"));
            System.setOut(ps);
            work(123456);
            System.setOut(out);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
     
    
    }
    
    private static void work(int n) {
        BigInteger x = BigInteger.valueOf(2);
        BigInteger y = BigInteger.valueOf(3);
        
        for(int i = 1; i < n; ++i) {
            BigInteger tmp1 = x.multiply(BigInteger.valueOf(2)).subtract(y.multiply(BigInteger.valueOf(3)));
            BigInteger tmp2 = x.multiply(BigInteger.valueOf(3)).add(y.multiply(BigInteger.valueOf(2)));
            x = tmp1;
            y = tmp2;
        }
        System.out.println(x + "" + y + "i");
    }
 
}

 

 輸入輸出流：

public static void main(String[] args) throws IOException {
            FileInputStream f2 = new FileInputStream("ans.txt"); 
            File f1 =new File("ant.txt");
            InputStreamReader ps = new InputStreamReader(f2,"utf8");
            PrintStream pw = new PrintStream(new FileOutputStream(f1));
            BufferedReader ff = new BufferedReader(ps);
            System.setOut(pw);
              String i;
              while((i=ff.readLine())!=null){
                  System.out.println(i);
              }
             
        }