Map implementation with duplicate keys

Question

I want to have a map with duplicate keys.

I know there are many map implementations (Eclipse shows me about 50), so I bet there must be one that allows this. I know

Answer 1

No fancy libs required. Maps are defined by a unique key, so dont bend them, use a list. Streams are mighty.

import java.util.AbstractMap.SimpleImmutableEntry;

List> nameToLocationMap = Arrays.asList(
    new SimpleImmutableEntry<>("A", "A1"),
    new SimpleImmutableEntry<>("A", "A2"),
    new SimpleImmutableEntry<>("B", "B1"),
    new SimpleImmutableEntry<>("B", "B1"),
);

And thats it. Usage examples:

List allBsLocations = nameToLocationMap.stream()
        .filter(x -> x.getKey().equals("B"))
        .map(x -> x.getValue())
        .collect(Collectors.toList());

nameToLocationMap.stream().forEach(x -> 
do stuff with: x.getKey()...x.getValue()...