一个例子 - 编程入门网

一个例子

//: NewIODemo.java
// Java 1.1 IO typical usage
import java.io.*;

public class NewIODemo {
  public static void main(String[] args) {
    try {
      // 1. Reading input by lines:
      BufferedReader in =
        new BufferedReader(
          new FileReader(args[0]));
      String s, s2 = new String();
      while((s = in.readLine())!= null)
        s2 += s + "\n";
      in.close();

      // 1b. Reading standard input:
      BufferedReader stdin =
        new BufferedReader(
          new InputStreamReader(System.in));      
      System.out.print("Enter a line:");
      System.out.println(stdin.readLine());

      // 2. Input from memory
      StringReader in2 = new StringReader(s2);
      int c;
      while((c = in2.read()) != -1)
        System.out.print((char)c);

      // 3. Formatted memory input
      try {
        DataInputStream in3 =
          new DataInputStream(
            // Oops: must use deprecated class:
            new StringBufferInputStream(s2));
        while(true)
          System.out.print((char)in3.readByte());
      } catch(EOFException e) {
        System.out.println("End of stream");
      }

      // 4. Line numbering & file output
      try {
        LineNumberReader li =
          new LineNumberReader(
            new StringReader(s2));
        BufferedReader in4 =
          new BufferedReader(li);
        PrintWriter out1 =
          new PrintWriter(
            new BufferedWriter(
              new FileWriter("IODemo.out")));
        while((s = in4.readLine()) != null )
          out1.println(
            "Line " + li.getLineNumber() + s);
        out1.close();
      } catch(EOFException e) {
        System.out.println("End of stream");
      }

      // 5. Storing & recovering data
      try {
        DataOutputStream out2 =
          new DataOutputStream(
            new BufferedOutputStream(
              new FileOutputStream("Data.txt")));
        out2.writeDouble(3.14159);
        out2.writeBytes("That was pi");
        out2.close();
        DataInputStream in5 =
          new DataInputStream(
            new BufferedInputStream(
              new FileInputStream("Data.txt")));
        BufferedReader in5br =
          new BufferedReader(
            new InputStreamReader(in5));
        // Must use DataInputStream for data:
        System.out.println(in5.readDouble());
        // Can now use the "proper" readLine():
        System.out.println(in5br.readLine());
      } catch(EOFException e) {
        System.out.println("End of stream");
      }

      // 6. Reading and writing random access
      // files is the same as before.
      // (not repeated here)

    } catch(FileNotFoundException e) {
      System.out.println(
        "

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