Bruce Eckel's Thinking in Java | Contents | Prev | Next |
//: 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( "File Not Found:" + args[1]); } catch(IOException e) { System.out.println("IO Exception"); } } } ///:~
//: IOBug.java // Java 1.1 (and higher?) IO Bug import java.io.*; public class IOBug { public static void main(String[] args) throws Exception { DataOutputStream out = new DataOutputStream( new BufferedOutputStream( new FileOutputStream("Data.txt"))); out.writeDouble(3.14159); out.writeBytes("That was the value of pi\n"); out.writeBytes("This is pi/2:\n"); out.writeDouble(3.14159/2); out.close(); DataInputStream in = new DataInputStream( new BufferedInputStream( new FileInputStream("Data.txt"))); BufferedReader inbr = new BufferedReader( new InputStreamReader(in)); // The doubles written BEFORE the line of text // read back correctly: System.out.println(in.readDouble()); // Read the lines of text: System.out.println(inbr.readLine()); System.out.println(inbr.readLine()); // Trying to read the doubles after the line // produces an end-of-file exception: System.out.println(in.readDouble()); } } ///:~
//: Redirecting.java // Demonstrates the use of redirection for // standard IO in Java 1.1 import java.io.*; class Redirecting { public static void main(String[] args) { try { BufferedInputStream in = new BufferedInputStream( new FileInputStream( "Redirecting.java")); // Produces deprecation message: PrintStream out = new PrintStream( new BufferedOutputStream( new FileOutputStream("test.out"))); System.setIn(in); System.setOut(out); System.setErr(out); BufferedReader br = new BufferedReader( new InputStreamReader(System.in)); String s; while((s = br.readLine()) != null) System.out.println(s); out.close(); // Remember this! } catch(IOException e) { e.printStackTrace(); } } } ///:~
has been deprecated.