CODEWITHSUNDEEP
javagenerics
Beau Johnny Bekkestad
Beau Johnny Bekkestad

Reputation: 381

variable length generic types

i want to do something like this, anyone done something similar? I have one solution map that has two keys, i am using it for geolocation, but i would like to make it with n number of keys instead.

import java.util.Collection;
import java.util.Set;

public interface NKeyMap<K..., V> {
    public void clear();
    public boolean containsKey(K...);
    public boolean containsValue(V value);
    public V get(K...);
    public boolean isEmpty();
    public V put(K..., V value);
    public V removeK..., V value);
    public int size();
    public Collection<V> values();
    public Set<K...> keys();
}

Upvotes: 3

Views: 2736

Answers (3)

Krushna
Krushna

Reputation: 6170

You can not do var-arg generic but you can do something like below

import java.util.Collection;
import java.util.Set;

public interface NKeyMap<K, V> {
    public void clear();
    public boolean containsKey(K... k );
    public boolean containsValue(V value);
    public V get(K... k);
    public boolean isEmpty();
    public V put(V value, K...k);
    public V remove(V value, K... k);
    public int size();
    public Collection<V> values();
    public Set<K> keys();
}

Upvotes: 2

Karthik T
Karthik T

Reputation: 31972

Take a look at this post The person tries to simulate this by chaining pair

He does this

Pair<String, Integer> pair = Pairs.pair("hello", 5);
Pair<Double, Pair<String, Integer>> withDouble = Pairs.pair(3.0, pair);

And proposes the below to make it cleaner

public class Pair<T, U> { ...
  public <V> Pair<V, Pair<T, U>> prepend(V v) {
   return pair(v, this); } }

So that it becomes 

Pair<Double, Pair<String, Integer>> pair = Pairs.pair("hello", 5).prepend(3.0);

Note: you might need to write Pair.

Note: Seems he actually endorses javatuples at the end..

More relevant:

After reading your comment, this more obvious solution presents itself. Multidimensional maps, much like multimensional arrays

Map<XKey, Map<YKey, Value> >

Upvotes: 2

qqilihq
qqilihq

Reputation: 11474

If you need variable-length keys, you can use javatuples or something similar, which wrap an arbitrary number and arbitrary types of arguments (they provide tuples until a length of 10):

Map<Triplet<Double,Float,Integer>, Object> mapWithCombinedKeys = ...

Upvotes: 1

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