| 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.