Java的I/O笔记（4）

Print流

PrintWriter 和 PrintStream 都属于输出流，前者字符流，后者字节流。

二者都提供了重载了的print和println方法，用于多种类型数据的输出。

二者的输出操作不会抛出异常，用户通过检测错误状态获取错误信息。

二者均有自动flush功能。

构造方法：

PrintWriter(Writer out)

PrintWriter(Writer out , boolean autoFlush)

PrintWriter(OutputStream out)

PrintWriter(OutputStream out , boolean autoFlush)

PrintStream(OutputStream out)

PrintStream(OutputStream out , boolean autoFlush)

 

   1:  import java.io.*;

   2:  public class TestPrintStream1 { 

   3:    public static void main(String[] args) {

   4:      PrintStream ps = null;

   5:      try {

   6:        FileOutputStream fos = 

   7:                new FileOutputStream("d:\\bak\\log.dat");

   8:        ps = new PrintStream(fos);

   9:      } catch (IOException e) {

  10:        e.printStackTrace();

  11:      }

  12:      if(ps != null){

13: System.setOut(ps); //原本out指向DOS窗口，现在用setOut方法将输出指向ps，

//也就是d:\\bak\\log.dat这个文件了

  14:      }

  15:      int ln = 0;

  16:      for(char c = 0; c <= 60000; c++){

  17:        System.out.print(c+ " ");

  18:        if(ln++ >=100){ System.out.println(); ln = 0;}

  19:      }

  20:    }

  21:  }

 

 

   1:  import java.io.*;

   2:  public class TestPrintStream2 {

   3:    public static void main(String[] args) {

   4:      

String filename = args[0];

           // 命令行参数

   5:      if(filename!=null){list(filename,System.out);}

   6:    }

   7:    public static void list(String f,PrintStream fs){

   8:      try {

   9:        BufferedReader br = 

  10:                    new BufferedReader(new FileReader(f));

  11:        String s = null; 

  12:        while((s=br.readLine())!=null){

  13:          fs.println(s);            

  14:        }

  15:        br.close();

  16:      } catch (IOException e) {

  17:        fs.println("无法读取文件");

  18:      }

  19:    }

  20:  }

 

   1:  import java.util.*; 

   2:  import java.io.*;

   3:  public class TestPrintStream3 {

   4:    public static void main(String[] args) {

   5:      String s = null;

   6:      BufferedReader br = new BufferedReader(

   7:                          new InputStreamReader(

System.in

));

   8:      try {

   9:        FileWriter fw = new FileWriter

  10:                             ("d:\\bak\\logfile.log", true);   //将字符流写到日志

11: PrintWriter log = new PrintWriter(fw);         //用PrintWriter包住FileWriter，

//因为FileWriter是Writer的子类

  12:        while ((s = 

br.readLine

())!=null) {      //之所以要把InputStreamReader包到BufferedReader里

                                                      //就是要用readline()这个方法

  13:          if(s.equalsIgnoreCase("exit")) break;

  14:          System.out.println(s.toUpperCase());

  15:          log.println("-----");

  16:          log.println(s.toUpperCase()); 

  17:          log.flush();

  18:        }

  19:        log.println("==="+

new Date()

+"==="); 

  20:        log.flush();

  21:        log.close();

  22:      } catch (IOException e) {

  23:        e.printStackTrace();

  24:      }

  25:    }

  26:  }

转载于:https://www.cnblogs.com/bevin-h/archive/2012/04/23/2466231.html