大数据库，很多地图？

Question

As part of a student project I am building a large database, which could theoretically contain millions of objects.

I'm starting with the firstname (ie Person fName = "John").

My plan is to convert "John" to a hashcode, convert the hashcode into an Integer, then store it in the map as - (as integer comparisons are faster).

Now here is my problem - To make the iteration faster, I want to have separate static maps, accessed depending on the first letter of the name. Like

public class FirstNameList {

    private static Map<Integer, String> a = new HashMap<Integer, String>();
    private static Map<Integer, String> b = new HashMap<Integer, String>();
    private static Map<Integer, String> c = new HashMap<Integer, String>();
    // etc

    public void addFName(String word) {
        if (word.length() == 0)
            throw new IllegalArgumentException("No name entered");
        word = word.toLowerCase();
        char x = word.charAt(0);

        Integer i = word.hashCode();

        x-correctMap.put(i, word);
    }

However it does not feel very efficient to have 26 if statements to pick the correct list. Does anyone know a way to pick the correct map? Or just better ideas in general?

Answer 1

I have three suggestions: the first is a direct answer to your question:

• First, you could store your maps in a map with the initial character as a key, then simply look up the correct map in the "master map."

• Second, this won't be any faster -- likely slower -- than simply storing everything in a single map. Never assume you're more clever than the authors of a library class without measurements to prove there's a problem.

• Third, you said "database", so why not use a database instead of all this? Postgres and MySQL are both free and easy to use, and will serve your needs well.

Answer 2

你可以嵌套你的地图，第一张地图的关键是字母。

Answer 3

You could have a list of maps, but you likely don't want to use a map at all. Something like TreeMap or a trie would work better, and allow you to have a single data structure.

Also, taking the hashcode of a string and then hashing is likely to be no faster than just using a String.