Didn't Java once have a Pair class? [duplicate]

Answer 1

Map.Entry

Java 1.6 and upper have two implementation of Map.Entry interface pairing a key with a value:

• AbstractMap.SimpleEntry
• AbstractMap.SimpleImmutableEntry

For example

Map.Entry < Month, Boolean > pair = 
    new AbstractMap.SimpleImmutableEntry <>( 
        Month.AUGUST , 
        Boolean.TRUE 
    )
;

pair.toString(): AUGUST=true

I use it when need to store pairs (like size and object collection).

This piece from my production code:

public Map>>>>>
        getEventTable(RiskClassifier classifier) {
    Map>>>>> l1s = new HashMap<>();
    Map>>> l2s = new HashMap<>();
    Map> l3s = new HashMap<>();
    List events = new ArrayList<>();
    ...
    map.put(l3s, events);
    map.put(l2s, new AbstractMap.SimpleImmutableEntry<>(l3Size, l3s));
    map.put(l1s, new AbstractMap.SimpleImmutableEntry<>(l2Size, l2s));
}

Code looks complicated but instead of Map.Entry you limited to array of object (with size 2) and lose type checks...