How to Create a Map with Multiple Keys for Value Access?

Implementing a Map with Multiple Keys

Question:

How can I create a data structure that behaves like a Map but uses multiple (differently-typed) keys to access its values? The keys are guaranteed to be unique. I need methods like getByKey1, getByKey2, containsKey1, and containsKey2.

Answer:

One approach is to use two internal Maps:

• Map
• Map

This method allows you to search values using either key because each key has its own Map.

Additional Notes:

• The suggestion of using a tuple or pair as a key for Java's Map would not work in this case because you need to be able to search values by only one of the two specified keys.

Example Code:

<code class="java">import java.util.HashMap;
import java.util.Map;

class MyMap<k1 k2 v> {
    private Map<k1 v> map1;
    private Map<k2 v> map2;

    public MyMap() {
        map1 = new HashMap();
        map2 = new HashMap();
    }

    public V getByKey1(K1 key) {
        return map1.get(key);
    }

    public V getByKey2(K2 key) {
        return map2.get(key);
    }

    public boolean containsKey1(K1 key) {
        return map1.containsKey(key);
    }

    public boolean containsKey2(K2 key) {
        return map2.containsKey(key);
    }

    public void put(K1 key1, K2 key2, V value) {
        map1.put(key1, value);
        map2.put(key2, value);
    }
}</k2></k1></k1></code>

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