4
/** Database implements a database of records */
public class Database
{ private Record[] base; // the collection of records
private int NOT_FOUND = -1; // int used to denote when a record not found
/** Constructor Database initializes the database
* @param initial size - the size of the database */
public Database(int initial_size)
{
if ( initial_size > 0 )
{ base = new Record[initial_size]; }
else { base = new Record[1]; }
}
/** findLocation is a helper method that searches base for a record
* whose key is k. If found, the index of the record is returned,
* else NOT FOUND is returned. */
private int findLocation(Key k)
{ int result = NOT_FOUND;
boolean found = false;
int i = 0;
while ( !found && i != base.length )
{
if ( base[i] != null && base[i].getKey().equals(k) )
{ found = true;
result = i;
}
else { i = i + 1; }
}
return result;
}
/** find locates a record in the database based on a key
* @param key - the key of the desired record
* @return (the address of) the desired record;
* return null if record not found. */
public Record find(Key k)
{ Record answer = null;
int index = findLocation(k);
if ( index != NOT_FOUND )
{ answer = base[index]; }
return answer;
}
/** insert inserts a new record into the database.
* @param r - the record
* @return true, if record added; return false if record not added because
* another record with the same key already exists in the database */
public boolean insert(Record r)
{ boolean success = false;
if ( findLocation(r.getKey()) == NOT_FOUND ) // r not already in base?
{ // find an empty element in base for insertion of r:
boolean found_empty_place = false;
int i = 0;
while ( !found_empty_place && i != base.length )
// so far, all of base[0]..base[i-1] are occupied
{
if ( base[i] == null ) // is this element empty?
{ found_empty_place = true; }
else { i = i + 1; }
}
if ( found_empty_place )
{ base[i] = r; }
else { // array is full! So, create a new one to hold more records:
Record[] temp = new Record[base.length * 2];
for ( int j = 0; j != base.length; j = j + 1 )
{ temp[j] = base[j]; } // copy base into temp
temp[base.length] = r; // insert r in first free element
base = temp; // change base to hold address of temp
}
success = true;
}
return success;
}
/** delete removes a record in the database based on a key
* @param key - the record's key (identification)
* @return true, if record is found and deleted; return false otherwise */
public boolean delete(Key k)
{ boolean result = false;
int index = findLocation(k);
if ( index != NOT_FOUND )
{ base[index] = null;
result = true;
}
return result;
}
}
Other class
================================================== ====
/** Record models a Library Book */
public class Record
{ // the names of the fields describe their contents:
private Key catalog_number;
private String title;
private String author;
private int publication_date;
/** Constructor Record constructs the book.
* @param num - the book's catalog number
* @param a - the book's author
* @param t - the book's title */
public Record(Key num, String a, String t, int date)
{ catalog_number = num;
title = t;
author = a;
publication_date = date;
//is_borrowed_by_someone = false;
}
/** getkey returns the key that identifies the record
* @return the key */
public Key getKey() {
return catalog_number; }
/** getTitle returns the book's title
* @return the title */
public String getTitle() {
return title; }
/** getAuthor returns the book's author
* @return the author */
public String getAuthor() {
return author; }
/** getDate returns the book's publication date
* @return the date */
public int getDate() {
return publication_date; }
}
Other class
================================================== ======
/** Key models a Library-of-Congress-style id number,
* consisting of a letter code concatenated to a decimal number */
public class Key
{ private String letter_code; // the letter code, e.g., "QA"
private double number_code; // the number code, e.g., 76.884
/** Constructor Key constructs a catalog number
* @param letters - the letter code, e.g., "QA"
* @param num - the decimal number code, e.g., 76.884 */
public Key(String letters, double num)
{ letter_code = letters;
number_code = num;
}
/** equals returns whether the catalog number held within this object
* is identical to the catalog number held within c
* @param c - the other catalog number
* @return true, if this catalog number equals c; return false, otherwise */
public boolean equals(Key c)
{ String s = c.getLetterCode();
double d = c.getNumberCode();
return ( s.equals(letter_code) && d == number_code );
}
/** getLetterCode returns the letter code part of this catalog number
* @return the letter code, e.g., "QA" */
public String getLetterCode() {
return letter_code; }
/** getNumberCode returns the number code part of this catalog number
* @return the number code, e.g., "76.884" */
public double getNumberCode() {
return number_code; }
}
And the main method (test method)
================================================== =====
public class Great
{
public static void main(String[] args)
{ Record r = new Record(new Key("QA", 78.8),"Charles Dicens","Great Expectations", 1860);
System.out.println(r);
Database library = new Database(5000);
System.out.println("Inserting is :" + (library.insert(r) ? " good" : "bad"));
Key k1 = new Key("QA", 78.8);
= library.find(k1);
System.out.println(r);
}
}
