Java HashTable实现get方法返回null？(Java HashTable Implementation get method returning null?)

 所以我需要编写这个程序，收到包含NFL球队名称和分数的17个文件（比如一个文件包含所有32支球队的得分，而另一个文件可能包含30个不同的得分，但是30个相同的球队，但当然省略了两个球队）。 我的教授为我们提供了一个HashTable实现，它通过在HashTable中的每个占用索引上创建某种LinkedList来处理冲突（我相当缺乏经验，所以如果我没有得到全部的话，我很抱歉术语正确，但希望你知道我的意思）。 我已经成功导入了所有文件和数据，并通过我教授给我们的碰撞处理将它们输入到HashTable中。 但是，每当我尝试为任何键调用get方法时，它都会返回“null”。 为什么是这样？ 我问，因为我需要找到每个团队的平均团队得分，而我无法想出这样做，因为get方法返回null。 任何帮助将非常感激！ 
 
 码： 
 
 HashEntry： 
 
public class HashEntry 
{
private String key;
private Double value;
private HashEntry next;

public HashEntry(String key, Double value) 
{
    this.key = key;
    this.value = value;
}

public String getKey() 
{
    return key;
}

public void setKey(String key) 
{
    this.key = key;
}

public Double getValue() 
{
    return value;
}

public void setValue(Double value) 
{
    this.value = value;
}

public HashEntry getNext() 
{
    return next;
}

public void setNext(HashEntry next) 
{
    this.next = next;
}

public boolean isNextEmpty()
{
    if(next.equals(null))
        return true;
    return false;
}
 
 哈希表： 
 
public class HashTable implements StringHashTable 
{
private HashEntry[] dataArray;
private int size;

public HashTable() 
{
    dataArray = new HashEntry[1000];
    size = 0;
}

private int hash(String key) 
{
    int sum = 0;
    for(int i = 0; i < key.length(); i++)
        sum += (int)key.charAt(i);

    return sum % dataArray.length;
}

@Override
public void put(String key, Double value) 
{
    HashEntry entry = new HashEntry(key, value);
    int indexToPut = hash(key);
    HashEntry cursor = dataArray[indexToPut];
    if(cursor != null) 
    {
        while(cursor.getNext() != null && cursor.getKey() != key) 
        {
            cursor = cursor.getNext();
        }
        if(cursor.getKey() != key) 
        {
            cursor.setNext(entry);
        } 
        else 
        {
            cursor.setValue(value);
        }
    } 
    else 
    {
        dataArray[indexToPut] = entry;
    }
    size++;
}

@Override
public Double get(String key) 
{
    int indexToGet = hash(key);
    HashEntry cursor = dataArray[indexToGet];
    while(cursor != null && cursor.getKey() != key) 
    {
        cursor = cursor.getNext();
    }
    if (cursor == null) 
    {
        return null;
    }
    return cursor.getValue();
}

@Override
public int size() 
{
    return size;
}

@Override
public void remove(String key) 
{
    int indexToRemove = hash(key);
    HashEntry cursor = dataArray[indexToRemove];
    HashEntry prev = null;
    while(cursor != null && cursor.getKey() != key) 
    {
        prev = cursor;
        cursor = cursor.getNext();
    }
    if (cursor != null) 
    {
        if (prev == null) 
        {
            dataArray[indexToRemove] = cursor.getNext();
        } 
        else 
        {
            prev.setNext(cursor.getNext());
        }
        size--;
    }
}

public String toString() 
{
    String res = "";
    for(HashEntry entry : dataArray) 
    {
        if (entry != null) 
        {
            HashEntry cursor = entry;
            while(cursor != null) 
            {
                res += cursor.getKey() + " = " + cursor.getValue() + "\n";
                cursor = cursor.getNext();
            }
        }
    }
    return res;
}
 
 驾驶员类： 
 
public class Project3 
{
static HashTable table = new HashTable();   
static HashMap<String, Double> table1 = new HashMap<String, Double>();
public static void main(String[] args) throws IOException
{
    //HashTableImpl<String, Double> table = new HashTableImpl<String, Double>();

    if (args.length < 1) 
    {
        System.out.println("Error: Directory name is missing");
        System.out.println("Usage: java scoreProcess directory_name");
        return;
    }

    File directory = new File(args[0]); // args[0] contains the directory name
    File[] files = directory.listFiles(); // get the list of files from that directory

    File file;
    Scanner input;

    // process the arguments stores in args
    for (int i = 0; i < files.length; i++) 
    {
        input = new Scanner(files[i]);

        //System.out.println("\nCurrent file name: " + files[i].getName());

        // no error checking done here, add your own
        String name;
        Double score;
        while(input.hasNext())
        {
            name = "";
            while(!input.hasNextDouble())
            {
                name += input.next() + " ";
            }
            score = input.nextDouble();
            //System.out.println("Name: " + name + " Score: " + score);
            table.put(name, score);
            table1.put(name, score);
        }
    }
    System.out.println("\n");
    System.out.println(table.toString());
    System.out.println(table.size());
    //System.out.println(table1.toString());
    System.out.println(table.get("Minnesota"));
}
}
 
 驱动程序输出： https ： //drive.google.com/file/d/0BwujWiqVRKKsNW52N1M2UllCeHc/view?usp=sharing 
 
 示例文本文件： 
 
New England 27
Indianapolis 24
Tennessee 17
Miami 7
St. Louis 17
Arizona 10
Seattle 21
New Orleans 7
NY Jets 31
Cincinnati 24
Pittsburgh 24
Oakland 21
Washington 16
Tampa Bay 10
San Diego 27
Houston 20
Jacksonville 13
Buffalo 10
Detroit 20
Chicago 16
Cleveland 20
Baltimore 3
Atlanta 21
San Francisco 19
Philadelphia 31
NY Giants 17
Minnesota 35
Dallas 17
Denver 34
Kansas City 24
Green Bay 24
Carolina 14

So I need to write this program that receives 17 files that contain NFL team names and scores (like one file contains scores for all 32 teams, while another file may contain 30 different scores for 30 of the same teams, but omitting two teams of course). And my professor provided us with a HashTable implementation to use, and it handles the collisions by creating some sort of LinkedList at each occupied index in the HashTable (I'm fairly inexperienced, so I'm sorry if I don't get the all the terminology correct, but hopefully you know what I mean). I have successfully imported all the files and data and have inputted them into the HashTable with the collision handling that my professor gave us. However, whenever I try to call the get method for any of the keys, it returns "null". Why is this? I ask because I need to find the average team score for each team, and I can't figure out to do this because the get method is returning null. Any help would be much appreciated!
 
Code: 
 
HashEntry:
 
public class HashEntry 
{
private String key;
private Double value;
private HashEntry next;

public HashEntry(String key, Double value) 
{
    this.key = key;
    this.value = value;
}

public String getKey() 
{
    return key;
}

public void setKey(String key) 
{
    this.key = key;
}

public Double getValue() 
{
    return value;
}

public void setValue(Double value) 
{
    this.value = value;
}

public HashEntry getNext() 
{
    return next;
}

public void setNext(HashEntry next) 
{
    this.next = next;
}

public boolean isNextEmpty()
{
    if(next.equals(null))
        return true;
    return false;
}
 
HashTable: 
 
public class HashTable implements StringHashTable 
{
private HashEntry[] dataArray;
private int size;

public HashTable() 
{
    dataArray = new HashEntry[1000];
    size = 0;
}

private int hash(String key) 
{
    int sum = 0;
    for(int i = 0; i < key.length(); i++)
        sum += (int)key.charAt(i);

    return sum % dataArray.length;
}

@Override
public void put(String key, Double value) 
{
    HashEntry entry = new HashEntry(key, value);
    int indexToPut = hash(key);
    HashEntry cursor = dataArray[indexToPut];
    if(cursor != null) 
    {
        while(cursor.getNext() != null && cursor.getKey() != key) 
        {
            cursor = cursor.getNext();
        }
        if(cursor.getKey() != key) 
        {
            cursor.setNext(entry);
        } 
        else 
        {
            cursor.setValue(value);
        }
    } 
    else 
    {
        dataArray[indexToPut] = entry;
    }
    size++;
}

@Override
public Double get(String key) 
{
    int indexToGet = hash(key);
    HashEntry cursor = dataArray[indexToGet];
    while(cursor != null && cursor.getKey() != key) 
    {
        cursor = cursor.getNext();
    }
    if (cursor == null) 
    {
        return null;
    }
    return cursor.getValue();
}

@Override
public int size() 
{
    return size;
}

@Override
public void remove(String key) 
{
    int indexToRemove = hash(key);
    HashEntry cursor = dataArray[indexToRemove];
    HashEntry prev = null;
    while(cursor != null && cursor.getKey() != key) 
    {
        prev = cursor;
        cursor = cursor.getNext();
    }
    if (cursor != null) 
    {
        if (prev == null) 
        {
            dataArray[indexToRemove] = cursor.getNext();
        } 
        else 
        {
            prev.setNext(cursor.getNext());
        }
        size--;
    }
}

public String toString() 
{
    String res = "";
    for(HashEntry entry : dataArray) 
    {
        if (entry != null) 
        {
            HashEntry cursor = entry;
            while(cursor != null) 
            {
                res += cursor.getKey() + " = " + cursor.getValue() + "\n";
                cursor = cursor.getNext();
            }
        }
    }
    return res;
}
 
Driver Class: 
 
public class Project3 
{
static HashTable table = new HashTable();   
static HashMap<String, Double> table1 = new HashMap<String, Double>();
public static void main(String[] args) throws IOException
{
    //HashTableImpl<String, Double> table = new HashTableImpl<String, Double>();

    if (args.length < 1) 
    {
        System.out.println("Error: Directory name is missing");
        System.out.println("Usage: java scoreProcess directory_name");
        return;
    }

    File directory = new File(args[0]); // args[0] contains the directory name
    File[] files = directory.listFiles(); // get the list of files from that directory

    File file;
    Scanner input;

    // process the arguments stores in args
    for (int i = 0; i < files.length; i++) 
    {
        input = new Scanner(files[i]);

        //System.out.println("\nCurrent file name: " + files[i].getName());

        // no error checking done here, add your own
        String name;
        Double score;
        while(input.hasNext())
        {
            name = "";
            while(!input.hasNextDouble())
            {
                name += input.next() + " ";
            }
            score = input.nextDouble();
            //System.out.println("Name: " + name + " Score: " + score);
            table.put(name, score);
            table1.put(name, score);
        }
    }
    System.out.println("\n");
    System.out.println(table.toString());
    System.out.println(table.size());
    //System.out.println(table1.toString());
    System.out.println(table.get("Minnesota"));
}
}
 
Driver Output: https://drive.google.com/file/d/0BwujWiqVRKKsNW52N1M2UllCeHc/view?usp=sharing
 
Example Text File: 
 
New England 27
Indianapolis 24
Tennessee 17
Miami 7
St. Louis 17
Arizona 10
Seattle 21
New Orleans 7
NY Jets 31
Cincinnati 24
Pittsburgh 24
Oakland 21
Washington 16
Tampa Bay 10
San Diego 27
Houston 20
Jacksonville 13
Buffalo 10
Detroit 20
Chicago 16
Cleveland 20
Baltimore 3
Atlanta 21
San Francisco 19
Philadelphia 31
NY Giants 17
Minnesota 35
Dallas 17
Denver 34
Kansas City 24
Green Bay 24
Carolina 14

原文：https://stackoverflow.com/questions/38517861