Pair and SmartMap

// Pair and SmartMap in action
// Problems:
// 1. this gives a compiler warning: "Type safety : A generic array of Pair<String,String> is created for a 
// varargs parameter"
// 2. All second elements of Pairs must be of same type, not even subclasses for it to compile.
public class Example {

    public static void main(String[] args) {
        SmartMap<String, String> myMap = map(of("key", "value1"), of("key2", "value 1"));
        System.out.println(myMap.get("key"));
    }
}


// Immutable tuple-ish thing
public class Pair<T, U> {
    
    private final T first;
    private final U second;

    // factory method
    public static <T, U> Pair<T, U> of(T first, U second) {
        return new Pair<T, U>(first, second);
    }
    
    public T first() {
        return first;
    }
    
    public U second() {
        return second;
    }
    
    private Pair(T first, U second) {
        this.first = first;
        this.second = second;
    }
    
    // equals() and hashcode() omitted
}

// Map that takes Pairs and unpacks them to traditional key/value
public class SmartMap<K, V> extends HashMap<K, V> {

    // factory method
    public static <K, V> SmartMap<K, V> map(Pair<K, V>... pairs) {
        return new SmartMap<K, V>().add(pairs);
    }
    
    public SmartMap<K, V> add(Pair<K, V>... pairs) {
        for (Pair<K, V> pair : pairs) {
            put(pair.first(), pair.second());
        }
        return this;
    }
    
    private SmartMap() { }
}