Programsprak/Java_Database/Linked.java

import java.awt.*;
import java.applet.*;
import java.io.*;
import java.util.*;

/** 
*  This is the mainfile containing functions for
*  this linked list with books. It also contains
*  the constructor List that generates a new list
*  called: myList. 
*
*
*       @author Christian Ohlsson, Karlstad university 1999
*       @version 1.3.4
*/
public class Linked {
  static List myList = new List(); 

/** 
*  This function opens up a file and reads it
*  line by line into a Stringbuffer. This
*  buffer gets later on splitted into different
*  categories by the StringTokenizer. The
*  token I have choosed is the ; character, 
*  which separates the different fields apart
*  in the file containing the data. After a
*  line is read and tokenized, different
*  variables is set in the node called myBook.
*  Every new node, book, is inserted into myList.
*/
  public static int loadBooks(){
    String s, token = ";";
    int rows = 0;
    try {
      BufferedReader infil = new BufferedReader(new FileReader("fil.dat")); 
      do {
        Book myBook = new Book();
        s = infil.readLine();
        StringTokenizer st  = new StringTokenizer(s, token); 
        myBook.subject      = st.nextToken(token);
        myBook.title        = st.nextToken(token);
        setAuthors(myBook, st.nextToken(token)); 
        myBook.publisher    = st.nextToken(token);
        myBook.year         = st.nextToken(token);
        myBook.into(myList);
        rows++;
      }while(true);
    } 
    catch(NoSuchElementException e1){System.err.println("No Such Element.");} 
    catch(FileNotFoundException e2){System.err.println("File Not Found.");}
    catch(IOException e3){System.err.println("I/O Error.");}
    catch(NullPointerException e4){}
    System.out.println("This database contains " + rows + " books.");
    return rows;
  } 

/** 
*  This function reads a line from STDIN by using
*  DataInputStream, and if the beginning character
*  is an 'x', the program quits, if no character
*  is given, the function restarts. 
*  If everything went OK, the search-string is sent
*  to a function called inCatalog(String s) for
*  further processing.
*/
  public static void search(int rows) {
    DataInputStream in = new DataInputStream(new BufferedInputStream(System.in));
    String s;
    try {
      for (int i = 0; i < rows ; i++) {
        System.out.print("\nBook register\n" + 
                         "Press 'x' to exit.\n" +
                         "############################################\n" +
                         "Search for: ");
        s = in.readLine(); 
        if(s.charAt(0) == 'x')
          break;
        else
          inCatalog(s, rows);
      }
    } 
    catch(IOException e1) { e1.printStackTrace(); }
    catch(StringIndexOutOfBoundsException e2) {
      System.out.println("Enter a value, or press 'x' to exit");
      search(rows);
    }
  } 

/**
*  This function calls the function myList.getElement
*  and gets every node, book, in the database. 
*  It then compares every value of the node to the
*  given String, and if it finds a match: the whole
*  node is printed out along with the number of entries
*  the search value found matches with. Otherwise, a 
*  message is printed out on the screen.
*/
  public static void inCatalog(String soktVarde, int rows) {
    int found = 0;
    try {
      for (int i=0 ; i<rows ; i++) {
        Book myBook = new Book();
        myBook = (Book)myList.getElement(i);
        if((myBook.subject.compareTo(soktVarde)    == 0) ||
           (myBook.title.compareTo(soktVarde)      == 0) ||
           (isAuthor(myBook.author, soktVarde)         ) ||
           (myBook.publisher.compareTo(soktVarde)  == 0) ||
           (myBook.year.compareTo(soktVarde)       == 0)) {
          found++;
          System.out.println("\nSubject \t"    + myBook.subject);
          System.out.println("Title \t\t"      + myBook.title);
          System.out.print("Author \t\t"       + myBook.allAuthors);
          System.out.println("\nPublisher \t"  + myBook.publisher);
          System.out.println("Year \t\t"       + myBook.year);
        }
      }
    }
    catch(NullPointerException e) {}
    if (found > 0)
      System.out.println("There were " + found + 
                         " entries in the database about " + 
                           soktVarde + ".");    
    else
      System.out.println("There's no information about " + 
                          soktVarde + " in this database");
  }
/**
*  This function recives an array of authors and a
*  search string. If then loops through the array
*  of authors and tries to locate the search string
*  in the array. Because I use indexOf for the search, 
*  the author Kernighan A. B will be found if the search
*  string is Kerni, rnighhan, or n A. B.
*  It returns true if the author was found, otherwise false. 
*/
  public static boolean isAuthor(String author[], String soktVarde) {
    try {
      int i=0;
      while(author[i] != null) {
        if(author[i].indexOf(soktVarde) >= 0)
          return true;
        i++;
      }
    }
    catch(NullPointerException e4){System.out.println("Null ptr in isAthor");}
    return false;
  }

/**
*  This function recieves a Book, and a String
*  containing all of the authors of a Book. It
*  the splits up the String, using the StringTokenizer
*  and puts the different authors in different
*  places in the array of authors of each Book. 
*/
  public static void setAuthors(Book myBook, String inString) {
    String token = ",";
    int i=0;
    myBook.allAuthors = inString;
    try {
      StringTokenizer st  = new StringTokenizer(inString, token); 
      while(st.hasMoreTokens()) {
        myBook.author[i] = st.nextToken(token);
        i++;
      }
    }
    catch(NoSuchElementException e1){System.err.println("No Such Element.");} 
    catch(NullPointerException e4){System.err.println("Null Pointer In setAuthors.");}
  }

/**
*  The main function really does'nt do much. 
*  It just calls the functions loadBooks()
*  and gets the number of Books in the database
*  from there and then calls the search-function
*  with the number of Books as a parameter.
*/
  public static void main(String args[]) {
    int rows = loadBooks();
    search(rows);
  }
}