DoubleKeyMap

```
public class DoubleKeyMap<Key1,Key2,Value>
extends Object
```
Sometimes we need to map a key to a value but key is two pieces of data. This nested hash table saves creating a single key each time we access map; avoids mem creation.

Constructors
Constructor and Description
`DoubleKeyMap()`

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`Map<Key2,Value>`	`get(Key1 k1)`
`Value`	`get(Key1 k1, Key2 k2)`
`Set<Key1>`	`keySet()` get all primary keys
`Set<Key2>`	`keySet(Key1 k1)` get all secondary keys associated with a primary key
`Value`	`put(Key1 k1, Key2 k2, Value v)`
`Collection<Value>`	`values(Key1 k1)` Get all values associated with primary key

public Value put(Key1 k1,
                 Key2 k2,
                 Value v)

public Value get(Key1 k1,
                 Key2 k2)

values
```
public Collection<Value> values(Key1 k1)
```
Get all values associated with primary key

keySet
```
public Set<Key2> keySet(Key1 k1)
```
get all secondary keys associated with a primary key

Class DoubleKeyMap<Key1,Key2,Value>