listing 1
// Read an array of bytes from the keyboard. 
 
import java.io.*; 
 
class ReadBytes { 
  public static void main(String args[]) 
    throws IOException { 
      byte data[] = new byte[10]; 
 
      System.out.println("Enter some characters."); 
      System.in.read(data); 
      System.out.print("You entered: "); 
      for(int i=0; i < data.length; i++) 
        System.out.print((char) data[i]); 
  } 
}

listing 2
// Demonstrate System.out.write(). 
class WriteDemo { 
  public static void main(String args[]) { 
    int b; 
 
    b = 'X'; 
    System.out.write(b); 
    System.out.write('\n'); 
  } 
}

listing 3
/* Display a text file. 
 
   To use this program, specify the name  
   of the file that you want to see. 
   For example, to see a file called TEST.TXT, 
   use the following command line. 
 
   java ShowFile TEST.TXT 
*/ 
 
import java.io.*; 
 
class ShowFile { 
  public static void main(String args[])  
    throws IOException 
  { 
    int i; 
    FileInputStream fin; 
 
    try { 
      fin = new FileInputStream(args[0]); 
    } catch(FileNotFoundException exc) { 
      System.out.println("File Not Found"); 
      return; 
    } catch(ArrayIndexOutOfBoundsException exc) { 
      System.out.println("Usage: ShowFile File"); 
      return; 
    } 
 
    // read bytes until EOF is encountered 
    do { 
      i = fin.read(); 
      if(i != -1) System.out.print((char) i); 
    } while(i != -1); 
 
    fin.close(); 
  } 
}

listing 4
/* Copy a text file. 
 
   To use this program, specify the name  
   of the source file and the destination file. 
   For example, to copy a file called FIRST.TXT 
   to a file called SECOND.TXT, use the following 
   command line. 
 
   java CopyFile FIRST.TXT SECOND.TXT 
*/ 
 
import java.io.*; 
 
class CopyFile { 
  public static void main(String args[])  
    throws IOException 
  { 
    int i; 
    FileInputStream fin; 
    FileOutputStream fout; 
 
    try { 
      // open input file 
      try { 
        fin = new FileInputStream(args[0]); 
      } catch(FileNotFoundException exc) { 
        System.out.println("Input File Not Found"); 
        return; 
      } 
 
      // open output file 
      try { 
        fout = new FileOutputStream(args[1]); 
      } catch(FileNotFoundException exc) { 
        System.out.println("Error Opening Output File"); 
        return; 
      } 
    } catch(ArrayIndexOutOfBoundsException exc) { 
      System.out.println("Usage: CopyFile From To"); 
      return; 
    } 
 
    // Copy File 
    try { 
      do { 
        i = fin.read(); 
        if(i != -1) fout.write(i); 
      } while(i != -1); 
    } catch(IOException exc) { 
      System.out.println("File Error"); 
    } 
 
    fin.close(); 
    fout.close(); 
  } 
}

listing 5
// Write and then read back binary data. 
import java.io.*; 
 
class RWData { 
  public static void main(String args[]) 
    throws IOException { 
     
    DataOutputStream dataOut; 
    DataInputStream dataIn; 
 
    int i = 10; 
    double d = 1023.56; 
    boolean b = true; 
 
    try { 
      dataOut = new 
          DataOutputStream(new FileOutputStream("testdata")); 
    } 
    catch(IOException exc) { 
      System.out.println("Cannot open file."); 
      return; 
    } 
 
    try { 
      System.out.println("Writing " + i); 
      dataOut.writeInt(i);  
 
      System.out.println("Writing " + d); 
      dataOut.writeDouble(d); 
 
      System.out.println("Writing " + b); 
      dataOut.writeBoolean(b); 
 
      System.out.println("Writing " + 12.2 * 7.4); 
      dataOut.writeDouble(12.2 * 7.4); 
 
    } 
    catch(IOException exc) { 
      System.out.println("Write error."); 
    } 
 
    dataOut.close(); 
 
    System.out.println(); 
 
    // Now, read them back. 
    try { 
      dataIn = new 
          DataInputStream(new FileInputStream("testdata")); 
    } 
    catch(IOException exc) { 
      System.out.println("Cannot open file."); 
      return; 
    } 
 
    try { 
      i = dataIn.readInt(); 
      System.out.println("Reading " + i); 
 
      d = dataIn.readDouble(); 
      System.out.println("Reading " + d); 
 
      b = dataIn.readBoolean(); 
      System.out.println("Reading " + b); 
 
      d = dataIn.readDouble(); 
      System.out.println("Reading " + d); 
    } 
    catch(IOException exc) { 
      System.out.println("Read error."); 
    } 
 
    dataIn.close();  
  } 
}

listing 6
/*   
   Project 10-1 
 
   Compare two files. 
 
   To use this program, specify the names   
   of the files to be compared on the command line. 
  
   java CompFile FIRST.TXT SECOND.TXT  
*/  
  
import java.io.*;  
  
class CompFiles {  
  public static void main(String args[])   
    throws IOException  
  {  
    int i=0, j=0;  
    FileInputStream f1;  
    FileInputStream f2;  
  
    try {  
      // open first file 
      try {  
        f1 = new FileInputStream(args[0]);  
      } catch(FileNotFoundException exc) {  
        System.out.println(args[0] + " File Not Found");  
        return;  
      }  
  
      // open second file  
      try {  
        f2 = new FileInputStream(args[1]);  
      } catch(FileNotFoundException exc) {  
        System.out.println(args[1] + " File Not Found");  
        return;  
      }  
    } catch(ArrayIndexOutOfBoundsException exc) {  
      System.out.println("Usage: CompFile f1 f2");  
      return;  
    }  
  
    // Compare files  
    try {  
      do {  
        i = f1.read();  
        j = f2.read();  
        if(i != j) break; 
      } while(i != -1 && j != -1);  
    } catch(IOException exc) {  
      System.out.println("File Error");  
    }  
    if(i != j)  
      System.out.println("Files differ."); 
    else 
      System.out.println("Files are the same."); 
  
    f1.close();  
    f2.close();  
  }  
}

listing 7
// Demonstrate random access files. 
import java.io.*; 
 
class RandomAccessDemo { 
  public static void main(String args[]) 
    throws IOException { 
 
    double data[] = { 19.4, 10.1, 123.54, 33.0, 87.9, 74.25 }; 
    double d; 
    RandomAccessFile raf; 
 
    try { 
      raf = new RandomAccessFile("random.dat", "rw"); 
    } 
    catch(FileNotFoundException exc) { 
      System.out.println("Cannot open file."); 
      return ; 
    } 
 
    // Write values to the file.      
    for(int i=0; i < data.length; i++) { 
      try { 
        raf.writeDouble(data[i]); 
      }  
      catch(IOException exc) { 
        System.out.println("Error writing to file."); 
        return ; 
      } 
    } 
 
    try { 
      // Now, read back specific values 
      raf.seek(0); // seek to first double 
      d = raf.readDouble(); 
      System.out.println("First value is " + d); 
 
      raf.seek(8); // seek to second double 
      d = raf.readDouble(); 
      System.out.println("Second value is " + d); 
 
      raf.seek(8 * 3); // seek to fourth double 
      d = raf.readDouble(); 
      System.out.println("Fourth value is " + d); 
 
      System.out.println(); 
 
      // Now, read every other value. 
      System.out.println("Here is every other value: "); 
      for(int i=0; i < data.length; i+=2) { 
        raf.seek(8 * i); // seek to ith double 
        d = raf.readDouble(); 
        System.out.print(d + " "); 
      } 
    }  
    catch(IOException exc) { 
      System.out.println("Error seeking or reading."); 
    } 
  
    raf.close(); 
  } 
}

listing 8
// Use a BufferedReader to read characters from the console. 
import java.io.*; 
 
class ReadChars { 
  public static void main(String args[])  
    throws IOException 
  { 
    char c; 
    BufferedReader br = new 
            BufferedReader(new InputStreamReader(System.in)); 
 
    System.out.println("Enter characters, period to quit."); 
 
    // read characters 
    do { 
      c = (char) br.read(); 
      System.out.println(c); 
    } while(c != '.'); 
  } 
}

listing 9
// Read a string from console using a BufferedReader. 
import java.io.*; 
 
class ReadLines { 
  public static void main(String args[])  
    throws IOException 
  { 
    // create a BufferedReader using System.in 
    BufferedReader br = new BufferedReader(new 
                            InputStreamReader(System.in)); 
    String str; 
 
    System.out.println("Enter lines of text."); 
    System.out.println("Enter 'stop' to quit."); 
    do { 
      str = br.readLine(); 
      System.out.println(str); 
    } while(!str.equals("stop")); 
  } 
}

listing 10
// Demonstrate PrintWriter. 
import java.io.*; 
 
public class PrintWriterDemo { 
  public static void main(String args[]) { 
    PrintWriter pw = new PrintWriter(System.out, true); 
    int i = 10; 
    double d = 123.67; 
 
    pw.println("Using a PrintWriter."); 
    pw.println(i); 
    pw.println(d); 
 
    pw.println(i + " + " + d + " is " + i+d); 
  } 
}

listing 11
/* A simple key-to-disk utilitiy that 
   demonstrates a FileWriter. */ 
 
import java.io.*; 
 
class KtoD { 
  public static void main(String args[])  
  throws IOException { 
 
    String str; 
    FileWriter fw; 
    BufferedReader br = 
            new BufferedReader( 
                  new InputStreamReader(System.in)); 
 
    try { 
      fw = new FileWriter("test.txt"); 
    } 
    catch(IOException exc) { 
      System.out.println("Cannot open file."); 
      return ; 
    } 
 
    System.out.println("Enter text ('stop' to quit)."); 
    do { 
      System.out.print(": "); 
      str = br.readLine(); 
 
      if(str.compareTo("stop") == 0) break;  
 
      str = str + "\r\n"; // add newline 
      fw.write(str); 
    } while(str.compareTo("stop") != 0); 
 
    fw.close(); 
  } 
}

listing 12
/* A simple disk-to-screen utilitiy that 
   demonstrates a FileReader. */ 
 
import java.io.*; 
 
class DtoS { 
  public static void main(String args[]) throws Exception { 
    FileReader fr = new FileReader("test.txt"); 
    BufferedReader br = new BufferedReader(fr); 
    String s; 
 
    while((s = br.readLine()) != null) { 
      System.out.println(s); 
    } 
 
    fr.close(); 
  } 
}

listing 13
/* This program averages a list of numbers entered  
   by the user.  */  
  
import java.io.*;  
  
class AvgNums {  
  public static void main(String args[])   
    throws IOException  
  {  
    // create a BufferedReader using System.in  
    BufferedReader br = new  
      BufferedReader(new InputStreamReader(System.in));  
    String str;  
    int n;  
    double sum = 0.0; 
    double avg, t;  
      
    System.out.print("How many numbers will you enter: ");  
    str = br.readLine(); 
    try { 
      n = Integer.parseInt(str); 
    }  
    catch(NumberFormatException exc) { 
      System.out.println("Invalid format"); 
      n = 0; 
    } 
    
    System.out.println("Enter " + n + " values."); 
    for(int i=0; i < n ; i++)  {  
      System.out.print(": "); 
      str = br.readLine();  
      try {  
        t = Double.parseDouble(str);  
      } catch(NumberFormatException exc) {  
        System.out.println("Invalid format");  
        t = 0.0;  
      }  
      sum += t;  
    }  
    avg = sum / n; 
    System.out.println("Average is " + avg); 
  }  
}

listing 14
#if 
if(condition) statement; 
else statement; 
 
#switch 
switch(expression) { 
  case constant: 
    statement sequence   
    break;   
    // ...   
  }   
 
#for 
for(init; condition; iteration) statement;   
 
#while 
while(condition) statement;   
 
#do 
do {   
  statement;   
} while (condition);   
 
#break 
break; or break label;   
 
#continue 
continue; or continue label;  

listing 15
/*   
   Project 10-2   
   
   A help program that uses a disk file 
   to store help information. 
*/   
 
import java.io.*; 
 
/* The Help class opens a help file, 
   searches for an topic, and then displays 
   the information associated with that topic. 
   Notice that it handles all I/O exceptions 
   itself, avoiding the need for calling  
   code to do so. */  
class Help { 
  String helpfile; // name of help file 
 
  Help(String fname) { 
    helpfile = fname; 
  } 
 
  // Display help on a topic. 
  boolean helpon(String what) {  
    FileReader fr; 
    BufferedReader helpRdr; 
    int ch; 
    String topic, info; 
 
    try { 
      fr = new FileReader(helpfile); 
      helpRdr = new BufferedReader(fr); 
    } 
    catch(FileNotFoundException exc) { 
      System.out.println("Help file not found."); 
      return false; 
    } 
    catch(IOException exc) { 
      System.out.println("Cannot open file."); 
      return false; 
    } 
 
    try { 
      do { 
        // read characters until a # is found 
        ch = helpRdr.read(); 
 
        // now, see if topics match 
        if(ch == '#') { 
          topic = helpRdr.readLine(); 
          if(what.compareTo(topic) == 0) { // found topic 
            do { 
              info = helpRdr.readLine(); 
              if(info != null) System.out.println(info); 
            } while((info != null) && 
                    (info.compareTo("") != 0)); 
            return true; 
          } 
        } 
      } while(ch != -1); 
    } 
    catch(IOException exc) { 
      System.out.println("File error."); 
      try { 
        helpRdr.close(); 
      }  
      catch(IOException exc2) { 
        System.out.println("Error closing file."); 
      } 
      return false; 
    } 
    try { 
      helpRdr.close(); 
    }  
    catch(IOException exc) { 
      System.out.println("Error closing file."); 
    } 
    return false; // topic not found 
  }  
  
  // Get a Help topic. 
  String getSelection() {  
    String topic = ""; 
 
    BufferedReader br = new BufferedReader( 
              new InputStreamReader(System.in)); 
 
    System.out.print("Enter topic: ");   
    try {   
      topic = br.readLine(); 
    } 
    catch(IOException exc) { 
      System.out.println("Error reading console."); 
    } 
    return topic; 
  } 
}  
  
// Demonstrate the file-based Help system. 
class FileHelp {   
  public static void main(String args[]) {   
    Help hlpobj = new Help("helpfile.txt");  
    String topic; 
 
    System.out.println("Try the help system. " + 
                       "Enter 'stop' to end.");  
    do {  
      topic = hlpobj.getSelection();   
 
      if(!hlpobj.helpon(topic)) 
        System.out.println("Topic not found.\n"); 
 
    } while(topic.compareTo("stop") != 0); 
  }  
}