Hashcode返回意外结果

Question

我正在尝试使用HashTable（我必须使用散列）来存储电话目录。我想根据姓氏（按字母顺序）输入电话条目。我决定使用条目中第一个字符的hashCode作为HashTable的键。

这是我在Entry类中编写的hashCode：

@Override
public int hashCode() {
    int index= getSurname().charAt(0);
    return index;
}

这是addEntry方法，用于向目录添加新条目：

@Override
public void addEntry(Entry line) {
    //Throws an exception if either surname, initials or number are null.
    if (line.getSurname()==null||line.getInitial()==null||line.getNumber()==null){
        throw new IllegalArgumentException("Please provide a Surname, Initials and a Number");
    }

    //Throws an exception if initials are less than 2
    if (line.getInitial().length() < 2) {
        throw new IllegalArgumentException("Please make sure that initials include both first name and surname eg: AK");
    }

    //Throws an exception if the length of the number is not 5 characters.
    if (line.getNumber().length() != 5) {
        throw new IllegalArgumentException("Please provide a Number that is 5 characters long (make sure that it starts with 0)");
    }

    //Throws an exception if the number doesnt start with 0.
    if (line.getNumber().startsWith("0") == false) {
        throw new IllegalArgumentException("The Number must start with a 0");
    }

    //Initialises the key using the hashCode of surname.
    int key=line.getSurname().hashCode();

    //If statement checks if the HashTable entries contains the key
    if (entries.contains(key)){
        //If it does it creates a linkedList called list
        LinkedList<Entry> list =new LinkedList();

        list=entries.get(key);
        ListIterator<Entry> iterator = list.listIterator();

        while (iterator.hasNext()){
            int x=0;
            String one = list.get(x).getSurname();

            if (one.compareToIgnoreCase(line.getSurname()) > 0){
                entries.put(x,list);
                x++;
                break;
            }
        }
    } else {
        LinkedList<Entry> list2 =new LinkedList();
        list2.add(line);
        entries.put(key,list2);
    }
}

问题是当我做一些测试以查看添加不同条目的结果时，我发现密钥（hashCode）未正确生成。

这些是结果：

Key: -2083437938. Value: [Entry{surname='Jansas initials=KJ Phone number=05544'}]
Key: -1911680082. Value: [Entry{surname='Paul initials=AP Phone number=05572'}]
Key: 66344. Value: [Entry{surname='Aza initials=AZ Phone number=05212'}]
Key: 867699843. Value: [Entry{surname='Penny initials=KP Phone number=05271'}]
Key: 1953849949. Value: [Entry{surname='Aanais initials=AP Phone number=05562'}]

姓氏“Aza”的条目不应该超过“Penny”而旁边的“Aanais”吗？关于如何解决问题的任何想法？

Answer 1

你写了

...
int key=line.getSurname().hashCode();
...

当我正确地看到它时，line变量的类型为Entry，你在hashCode类中覆盖Entry。以上剪辑应该是

...
int key=line.hashCode();
...

否则你使用类hashCode的String方法（或者getSurname返回的任何方法）。

但是，这不是Java哈希代码的良好实现，Java哈希代码不是为您的用例设计的。我会重新考虑你在这里用来排序的方法。