我试图建立一个通用对象的链表。我有链接列表现在我必须加载一个电影文件（在电影类我有流派，评级，标题）。首先我需要加载电影的CVS文件创建哈希表对象，其中包含一个链接列表数组反过来存储电影的对象。所以例如在电影课中我会有很多类型和流派。我想得到类型的哈希码，然后将其存储在阵列链表的哈希表中。这就是我使用LoadingMovie类的原因。
我不知道我在做什么，因为我第一次使用哈希表和链接列表等。这是我到目前为止所做的：
public class List<T> {
private Node<T> head;
private Node<T> tail;
private int count;
public void append(T d) {
if (head == null) {
head = tail = new Node<T>(d);
} else {
tail.insertAfter(d);
tail = tail.getNext();
count++;
}
}
public void prepend(T d) {
if (head == null) {
head = tail = new Node<T>(d);
} else {
head.insertBefore(d);
head = head.getPrevious();
count++;
}
}
public void removeHead() {
if (head == null) {
return;
} else if (head == tail) {
head = tail = null;
count--;
return;
}
head = head.getNext();
count--;
}
public ListIterator<T> getIterator() {
return new ListIterator<T>(this, head);
}
public void add(ListIterator<T> iter, T data) {
if (iter.getList() != this) {
return;
}
if (!iter.isValid()) {
append(data);
} else {
iter.getCurrentNode().insertAfter(data);
count++;
if (iter.getCurrentNode() == tail) {
tail = iter.getCurrentNode().getNext();
}
}
}
public void remove(ListIterator<T> iter) {
if (iter.getList() != this) {
return;
}
Node<T> node = iter.getCurrentNode();
if (node == null) {
return;
} else if (node == head) {
removeHead();
} else if (node == tail) {
removeTail();
} else {
Node<T> ptn = node.getPrevious();
ptn.setNext(node.getNext());
node.getNext().setPrevious(ptn);
iter.advance();
count--;
}
}
public void removeTail() {
if (head == null) {
} else if (head == tail) {
head = tail = null;
count--;
} else {
Node<T> node = head;
while (node.getNext() != tail) {
node = node.getNext();
}
tail = node;
tail.setNext(null);
count--;
}
}
public void display() {
ListIterator<T> iter = getIterator();
do {
System.out.println(iter.item()+ " , ");
iter.advance();
} while (iter.isValid());
}
public void displayReverse() {
ListIterator<T> iter = getIterator();
iter.end();
do {
System.out.print(iter.item() + " , ");
iter.previous();
} while (iter.isValid());
}
public Node<T> getHead() {
return head;
}
public Node<T> getTail() {
return tail;
}
public int getCount() {
return count;
}
public void setHead(Node<T> head) {
this.head = head;
}
public void setTail(Node<T> tail) {
this.tail = tail;
}
public void setCount(int count) {
this.count = count;
}
@Override
public int hashCode() {
int hash = 5;
hash = 89 * hash + Objects.hashCode(this.head);
hash = 89 * hash + Objects.hashCode(this.tail);
hash = 89 * hash + this.count;
return hash;
}
@Override
public boolean equals(Object obj) {
if (obj == null) {
return false;
}
if (getClass() != obj.getClass()) {
return false;
}
final List<?> other = (List<?>) obj;
if (!Objects.equals(this.head, other.head)) {
return false;
}
if (!Objects.equals(this.tail, other.tail)) {
return false;
}
if (this.count != other.count) {
return false;
}
return true;
}
this is the node class :
public class Node<T> {
T anElement;
Node<T> next;
Node<T> previous;
public Node() {
anElement = null;
next = null;
}
public Node(T elem) {
anElement = elem;
next = null;
}
public T getAnElement() {
return anElement;
}
public void setAnElement(T anElement) {
this.anElement = anElement;
}
public Node<T> getNext() {
return next;
}
public void setNext(Node<T> next) {
this.next = next;
}
public Node<T> getPrevious() {
return previous;
}
public void setPrevious(Node<T> previous) {
this.previous = previous;
}
@Override
public String toString() {
return "MyNode{" + "anElement=" + anElement + ", next=" + next + '}';
}
public void insertAfter(T nextData) {
if (nextData == null) {
return;
}
Node s = new Node(nextData);
s.setNext(next);
s.setPrevious(this);
if (next != null) {
next.setPrevious(s);
}
next = s;
}
public void insertBefore(T data) {
if (data == null) {
return;
}
Node s = new Node(data);
s.setNext(this);
s.setPrevious(previous);
if (previous != null) {
previous.setNext(s);
}
previous = s;
}
}
this is the load file class :
public class LoadingMovies {
private static final int size = 127;
private static HashMap<String, Movies> hash = new HashMap(size);
public static void loadMovies(String filename) {
String split = ","; //split with comma
try {
Scanner in = new Scanner(new File(filename));
String wordIn;
//List<Movies> linked = new List<>();
while (in.hasNextLine()) {
wordIn = in.nextLine();
String splitter[] = wordIn.split(split);
String movieTitle = splitter[0];
String movieGenre = splitter[1];
String ageRating = splitter[2];
double scoreRating = Double.parseDouble(splitter[3]);
Movies movie = new Movies();
movie.setTitle(movieTitle);
movie.setGenre(movieGenre);
movie.setAgeRating(ageRating);
movie.setScoreRating(scoreRating);
hash.find(movie.getGenre());
hash.insert(movie.getGenre(), movie);
hash.display();
}
} catch (FileNotFoundException e) {
System.out.println("Exception occured in the loadMovies() method in the Loadingovies class");
}
}
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
String filename = input.next();
loadMovies(filename);
}
this is the hash map method:
public class HashMap<KeyType,DataType>
{
private int count;
private int size;
private List<HashEntry<KeyType,DataType>> [] table;
public HashMap() {
}
public HashMap(int num)
{
size = num;
table = new List[num];
for(int i = 0; i < num; i++){
table[i] = new List<HashEntry<KeyType,DataType>>();
}
}
public void insert(KeyType key, DataType data){
if(key != null && data != null){
int hash = key.hashCode() % size;
HashEntry<KeyType, DataType> obj = new HashEntry(key, data);
table[hash].append(obj);
count++;
}
}
public void display(){
for(int i = 0 ; i < size; i++){
System.out.println("tables" + i + " ");
table[i].display();
}
}
public DataType find(KeyType key){
int hash = key.hashCode() % size;
List<HashEntry<KeyType,DataType>> list = table[hash];
ListIterator <HashEntry<KeyType, DataType>> iter = list.getIterator();
while(iter.isValid()){
if(iter.item().getKey().equals(key)){
return iter.item().getData();
}
iter.advance();
}
return null;
}
public void remove(KeyType key){
int hash = key.hashCode() % size;
List<HashEntry<KeyType,DataType>> list = table[hash];
ListIterator <HashEntry<KeyType, DataType>> iter = list.getIterator();
while(iter.isValid()){
if(iter.item().getKey().equals(key)){
list.remove(iter);
}
iter.advance();
}
}
}
and this is what i have for movie class:
public class Movies {
private String title;
private String genre;
private String ageRating;
private double scoreRating;
public Movies() {
title = "";
genre = "";
ageRating = "";
scoreRating = 0;
}
public Movies(String title, String genre, String ageRating, double scoreRating) {
this.title = title;
this.genre = genre;
this.ageRating = ageRating;
this.scoreRating = scoreRating;
}
public String getTitle() {
return title;
}
public String getGenre() {
return genre;
}
public String getAgeRating() {
return ageRating;
}
public double getScoreRating() {
return scoreRating;
}
public void setTitle(String title) {
this.title = title;
}
public void setGenre(String genre) {
this.genre = genre;
}
public void setAgeRating(String ageRating) {
this.ageRating = ageRating;
}
public void setScoreRating(double scoreRating) {
this.scoreRating = scoreRating;
}
@Override
public boolean equals(Object obj) {
if (obj == null) {
return false;
}
if (getClass() != obj.getClass()) {
return false;
}
final Movies other = (Movies) obj;
if (!Objects.equals(this.title, other.title)) {
return false;
}
if (!Objects.equals(this.genre, other.genre)) {
return false;
}
if (!Objects.equals(this.ageRating, other.ageRating)) {
return false;
}
if (Double.doubleToLongBits(this.scoreRating) != Double.doubleToLongBits(other.scoreRating)) {
return false;
}
return true;
}
@Override
public int hashCode() {
int hash = 11;
hash = (int) ((hash * 10) + scoreRating);
if (this.title != null) {
hash = (hash * 10) + title.hashCode();
}
if (this.genre != null) {
hash = (hash * 10) + genre.hashCode();
}
if (this.ageRating != null) {
hash = (hash * 10) + ageRating.hashCode();
}
return hash;
}
@Override
public String toString() {
String statement = "Movie Title:" + title + "\n" + "Movie Genre:" + genre + "\n" + "Age Rating: " + ageRating + "\n" + "User Score: " + scoreRating + "\n";
return statement;
}
我做错了什么:( 我得到空指针异常arrayoutofboundexceptions 一些电影打印，我得到大量的空表：＆＃39;（
答案 0 :(得分：0)
这里的问题是将对象映射到存储桶。这行代码......
int hash = key.hashCode() % size;
能够产生负值。 key.hashCode（）可以是负数，负数上％运算符的结果是负数。这就是导致ArrayIndexOutOfBounds异常的原因。最简单的解决方案是使用hashCode的绝对值...
int hash = Math.abs(key.hashCode()) % size;