Java Demo Program 2

See the notes at the bottom of the page, after the program listing...

import java.io.*;   // Import the Input and Output Stream Classes
import java.util.Vector;
import java.util.StringTokenizer;

public class JavaDemo2{

   public int getNumValue(String str)
   {
      Integer tempInt;
      int startPos;
      String numString = new String();
      String trimmedString;
      String tempStr = "this is a line with strings and a number";
    
      startPos = tempStr.length();
      numString = str.substring(startPos);
      trimmedString = numString.trim(); //trims whitespace from both ends
      
      System.out.println("Number is " + trimmedString);
      
      tempInt = Integer.valueOf(trimmedString); 
      return tempInt.intValue();
   }

   public Vector getIntVector(String str)
   {
      StringTokenizer tokens = new StringTokenizer(str);
      String tempStr;
      Vector tempVector = new Vector(tokens.countTokens());
      Integer tempInteger;

      while (tokens.hasMoreElements())
      {
         tempStr = tokens.nextToken();
         tempInteger = new Integer(tempStr);
         tempVector.addElement(tempInteger);
      }
      return tempVector;
   }

   public void printVector(Vector intVector)
   {
      int i;
      Integer tempInteger;

      for(i = 0; i < intVector.size(); i++)
      {
         tempInteger = (Integer)intVector.elementAt(i);
         System.out.print("" + tempInteger.intValue() + "  ");
      }
      System.out.println();
   }
 
   public static void main(String[] args){

      String infileName = new String("sampleFile.txt");
      String outfileName = new String("sampleFileOut.txt");
      String sample = new String("String+nulls\0\0\0\0\0");
      char sample2[] = new char[80];
      int numValue;
      boolean arrayNumbers=false;
      Vector intVector;

      sample2 = ("Another string with nulls:\0\0\0\0\0\0\0\0\0").toCharArray();
      System.out.println("String with null: " + sample + " characters");
      System.out.println("Another sample with nulls: " + 
             String.copyValueOf(sample2));
      JavaDemo2 testRun = new JavaDemo2();
      try{
         BufferedReader infile =
                new BufferedReader(new FileReader(infileName));	  
                                               // Open for reading
         System.out.println("File open for reading...");
         BufferedWriter outfile = 
                   new BufferedWriter(new FileWriter(outfileName));	
                               // Open for writing
         System.out.println("File open for writing...");
         String line;  
         while((line = infile.readLine()) != null)
         {
            System.out.println(line);	// routes output to CRT
            if (line.startsWith("this is a line with strings and a number"))
            {
               numValue = testRun.getNumValue(line);
               System.out.println("This line has the number: " + numValue);
            }
            if (arrayNumbers)
            {
               intVector = new Vector();
               intVector = testRun.getIntVector(line);
               System.out.print("Here's the array: ");
               testRun.printVector(intVector);
            } 
            if (line.startsWith("5 more numbers:")) 
               arrayNumbers = true;
            else arrayNumbers = false;
            outfile.write(line, 0, line.length());  // routes output to file
				outfile.newLine();
         }
         System.out.println("Done copying file...");
         infile.close();
         outfile.close();
         System.out.println("Files closed.");
      }
      catch(IOException e){
            System.err.println(e);
            return;
}}}

Notes about the above program:

• Two of the special classes that this program uses are:
  Vector and StringTokenizer
  These two classes are in the java.util package and are "imported" at the top of
  the program
• First look at main(). Three strings are initialized using the format:
  String stringname = new String("stringvalue");
  
• An alternative format that is special for Strings is:
  String stringname = "stringvalue";
  With this version, "new String()" is automatically invoked by Java
• Character arrays are initialized with the format:
  char sample2[] = new char[80]; allocating space for 80 characters.
  Note: in Java, character arrays do not end in the null char as in C and C++
• In a character array (but not in a String), values can be added separately:
  char[0]='A'; char[1]='B'; etc.
• Character arrays can also be initialized from Strings, using the toCharArray() method:
  sample2 = ("This is a string").toCharArray();
  OR: String str = "Hello world";
  sample2 = str.toCharArray();
• An instance of class JavaDemo2 is created:
  JavaDemo2 testRun = new JavaDemo2()
  This allows access to the functions defined outside of main()
  
• For instance, to call the getIntArray() function, the syntax is:
  testRun.getIntArray(line); //Converts a string of numbers into an integer Vector
• If the function is declared as static:
  public static Vector getIntArray(String str)...
  The function call would be simply: getIntArray(line)
• The program reads a text file line by line, where each line is a String
  The String is read using the method readLine():
  line = infile.readLine()
• The try-catch block is only necessary here because we are reading/writing to
  a file. If there is a problem opening the file, an exception will be "thrown"
  and "caught" by the catch block.
• Use the class String's startsWith() method to parse a command line into
  a command and a number following the command. (Like: LOAD 0)
  
• The syntax for startsWith() is:
  if (line.startsWith("String value")) ...
  For more information on methods available in the String class, see the Java API site
  
• This program demonstrates using the Vector class to contain a collection
  of Integer's. Note that class Integer is different from int.
  Look at the Java API site for more info about class Integer.