Examples for Java 1.7 or earlier I/O System -TIJ4

Think in Java (Fourth Edition) 

Chap.18

18.6.1 緩衝輸入文件

//: io/BufferedInputFile.java
import java.io.*;

public class BufferedInputFile {
  // Throw exceptions to console:
  public static String
  read(String filename) throws IOException {
    // Reading input by lines:
    BufferedReader in = new BufferedReader(
      new FileReader(filename));
    String s;
    StringBuilder sb = new StringBuilder();
    while((s = in.readLine())!= null)
      sb.append(s + "\n");
    in.close();
    return sb.toString();
  }
  public static void main(String[] args)
  throws IOException {
    System.out.print(read("BufferedInputFile.java"));
  }
} /* (Execute to see output) *///:~

18.6.2 從內存輸入

//: io/MemoryInput.java
import java.io.*;

public class MemoryInput {
  public static void main(String[] args)
  throws IOException {
    StringReader in = new StringReader(
      BufferedInputFile.read("MemoryInput.java"));
    int c;
    while((c = in.read()) != -1)
      System.out.print((char)c);
  }
} /* (Execute to see output) *///:~

18.6.3 格式化的內存輸入

//: io/FormattedMemoryInput.java
import java.io.*;

public class FormattedMemoryInput {
  public static void main(String[] args)
  throws IOException {
    try {
      DataInputStream in = new DataInputStream(
        new ByteArrayInputStream(
         BufferedInputFile.read(
          "FormattedMemoryInput.java").getBytes()));
      while(true)
        System.out.print((char)in.readByte());
    } catch(EOFException e) {
      System.err.println("End of stream");
    }
  }
} /* (Execute to see output) *///:~

//: io/TestEOF.java
// Testing for end of file while reading a byte at a time.
import java.io.*;

public class TestEOF {
  public static void main(String[] args)
  throws IOException {
    DataInputStream in = new DataInputStream(
      new BufferedInputStream(
        new FileInputStream("TestEOF.java")));
    while(in.available() != 0)
      System.out.print((char)in.readByte());
  }
} /* (Execute to see output) *///:~

18.6.4 基本的文件輸出

//: io/BasicFileOutput.java
import java.io.*;

public class BasicFileOutput {
  static String file = "BasicFileOutput.out";
  public static void main(String[] args)
  throws IOException {
    BufferedReader in = new BufferedReader(
      new StringReader(
        BufferedInputFile.read("BasicFileOutput.java")));
    PrintWriter out = new PrintWriter(
      new BufferedWriter(new FileWriter(file)));
    int lineCount = 1;
    String s;
    while((s = in.readLine()) != null )
      out.println(lineCount++ + ": " + s);
    out.close();
    // Show the stored file:
    System.out.println(BufferedInputFile.read(file));
  }
} /* (Execute to see output) *///:~

//: io/FileOutputShortcut.java
import java.io.*;

public class FileOutputShortcut {
  static String file = "FileOutputShortcut.out";
  public static void main(String[] args)
  throws IOException {
    BufferedReader in = new BufferedReader(
      new StringReader(
       BufferedInputFile.read("FileOutputShortcut.java")));
    // Here's the shortcut:
    PrintWriter out = new PrintWriter(file);
    int lineCount = 1;
    String s;
    while((s = in.readLine()) != null )
      out.println(lineCount++ + ": " + s);
    out.close();
    // Show the stored file:
    System.out.println(BufferedInputFile.read(file));
  }
} /* (Execute to see output) *///:~

18.6.5 存儲和數據恢復

//: io/StoringAndRecoveringData.java
import java.io.*;

public class StoringAndRecoveringData {
  public static void main(String[] args)
  throws IOException {
    DataOutputStream out = new DataOutputStream(
      new BufferedOutputStream(
        new FileOutputStream("Data.txt")));
    out.writeDouble(3.14159);
    out.writeUTF("That was pi");
    out.writeDouble(1.41413);
    out.writeUTF("Square root of 2");
    out.close();
    DataInputStream in = new DataInputStream(
      new BufferedInputStream(
        new FileInputStream("Data.txt")));
    System.out.println(in.readDouble());
    // Only readUTF() will recover the
    // Java-UTF String properly:
    System.out.println(in.readUTF());
    System.out.println(in.readDouble());
    System.out.println(in.readUTF());
  }
} /* Output:
3.14159
That was pi
1.41413
Square root of 2
*///:~

18.6.6 讀寫隨機訪問文件

//: io/UsingRandomAccessFile.java
import java.io.*;

public class UsingRandomAccessFile {
  static String file = "rtest.dat";
  static void display() throws IOException {
    RandomAccessFile rf = new RandomAccessFile(file, "r");
    for(int i = 0; i < 7; i++)
      System.out.println(
        "Value " + i + ": " + rf.readDouble());
    System.out.println(rf.readUTF());
    rf.close();
  }
  public static void main(String[] args)
  throws IOException {
    RandomAccessFile rf = new RandomAccessFile(file, "rw");
    for(int i = 0; i < 7; i++)
      rf.writeDouble(i*1.414);
    rf.writeUTF("The end of the file");
    rf.close();
    display();
    rf = new RandomAccessFile(file, "rw");
    rf.seek(5*8);
    rf.writeDouble(47.0001);
    rf.close();
    display();
  }
} /* Output:
Value 0: 0.0
Value 1: 1.414
Value 2: 2.828
Value 3: 4.242
Value 4: 5.656
Value 5: 7.069999999999999
Value 6: 8.484
The end of the file
Value 0: 0.0
Value 1: 1.414
Value 2: 2.828
Value 3: 4.242
Value 4: 5.656
Value 5: 47.0001
Value 6: 8.484
The end of the file
*///:~