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ArticleTable.java
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ArticleTable.java
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/*
* ArticleTable.java
*
* Dumblist rewritten as a hashtable
*
* Author: Theresa McNeil ([email protected])
* Date: March 24, 2014
*/
import java.util.Iterator;
public class ArticleTable implements Iterable<Article>{
private final int SIZE = 2503;
Node [] Table = new Node [SIZE];
public static class Node {
public Article data;
public Node next;
public Node(Article data, Node n) {
this.data = data;
this.next = n;
}
public Node(Article data) {
this(data, null);
}
}
// print out a string representation of the Article Table
public String toString(){
String t = "";
for(int i = 0; i < SIZE; i++){
if(Table[i] != null){
String s = Integer.toString(sfold(Table[i].data.getTitle(), SIZE));
t += "[" + s + "]->";
for(Node q = Table[i]; q != null; q = q.next){
t += q.data.getTitle();
}
t += "\n";
}
}
return t;
}
// insert a into the table using the title of a as the hash key
public void insert(Article a){
Table[hash(a.getTitle())] = insert(a, Table[hash(a.getTitle())]);
}
private Node insert(Article a, Node p){
Node q = new Node(a, p);
return q;
}
// deletes a title from the table
public void delete(String title){
Table[hash(title)] = delete(title, Table[hash(title)]);
}
private Node delete(String title, Node p){
for(Node q = p; q != null; q = q.next){
if(title.equals(q.data.getTitle())){
if(q.next == null)
return null;
else
q = q.next;
}
}
return p;
}
public boolean member(String title){
return(member(title, Table[hash(title)]));
}
private boolean member(String title, Node q){
for(Node p = q; p != null; p = p.next){
if(p.data.getTitle().compareTo(title) == 0)
return true;
}
return false;
}
public Article lookup(String title){
return lookup(title, Table[hash(title)]);
}
private Article lookup(String title, Node q){
if(member(title)){
for(Node p = q; p != null; p = p.next){
if(p.data.getTitle().equals(title))
return new Article(p.data.getTitle(), p.data.getBody());
else
return null;
}
return null;
}
else
return null;
}
public int getSize(){
return SIZE;
}
public void initialize(Article[] A) {
for(int i = 0; i < A.length; ++i)
insert(A[i]);
}
public Iterator<Article> iterator(){
return new It();
}
private class It implements Iterator<Article> {
private int cursor;
private Node head;
public It(){
for(; cursor < SIZE; cursor++){
if(Table[cursor] != null){
head = Table[cursor];
break;
}
}
}
public boolean hasNext(){
return head != null;
}
public Article next(){
Node temp = head;
head = head.next;
if(head == null){
cursor++;
for(; cursor < SIZE; cursor++){
if(Table[cursor] != null){
head = Table[cursor];
break;
}
}
}
return temp.data;
}
public void remove(){
}
}
// hash function for strings
int sfold(String s, int M){
int intLength = s.length() / 4;
int sum = 0;
for(int j = 0; j < intLength; j ++){
char c[] = s.substring(j * 4, (j * 4) + 4).toCharArray();
int mult = 1;
for(int k = 0; k < c.length; k++){
sum += c[k] * mult;
mult *= 256;
}
}
char c[] = s.substring(intLength * 4).toCharArray();
int mult = 1;
for(int k = 0; k < c.length; k++){
sum += c[k] * mult;
mult *= 256;
}
return (Math.abs(sum) % M);
}
int hash(String s){
int k = sfold(s, SIZE);
return(k % SIZE);
}
// Unit Tests
public static void main(String[] args){
System.out.println("Unit Test for Article Table");
ArticleTable Table = new ArticleTable();
ArticleTable TestTable = new ArticleTable();
Iterator<Article> it = Table.iterator();
// don't change next 2 lines
String dbPath = "articles/";
DatabaseIterator db = new DatabaseIterator(dbPath);
while(db.hasNext()){
Article a = db.next();
Table.insert(a);
//System.out.println(a);
}
//System.out.println(Table);
Article ocean = new Article("ocean", "the ocean is blue");
Article California = new Article("California", "California is on the west coast");
Article coast = new Article("coast", "the coast is near the ocean");
System.out.println("Testing insert...");
TestTable.insert(ocean);
System.err.println("inserting ocean, should give you \n[1163]->ocean");
System.out.println(TestTable.toString());
TestTable.insert(California);
TestTable.insert(coast);
System.err.println("inserting California and coast, should give you");
System.err.println("[329]->coast \n[1163]->ocean \n[1594]->California");
System.out.println(TestTable.toString());
System.out.println("Testing delete...");
TestTable.delete("California");
System.err.println("deleting California, new ArticleTable is");
System.err.println("[329]->coast \n[1163]->ocean");
System.out.println(TestTable);
System.out.println("Testing member...");
System.err.println("member(\"ocean\") should return \ntrue");
System.out.println(TestTable.member("ocean"));
System.err.println("\nmember(\"California\") should return \nfalse");
System.out.println(TestTable.member("California"));
System.out.println("\nTesting lookup...");
System.err.println("\nlooking up \"ocean\" should return");
System.err.println("ocean \n===== \nthe ocean is blue");
System.out.println(TestTable.lookup("ocean"));
System.err.println("looking up \"California\" should return");
System.err.println("null");
System.out.println(TestTable.lookup("California"));
}
}