18 — Generics

1List<String> names = new ArrayList<>();2names.add("Ravi");3// names.add(42);   // COMPILE ERROR — type safe!4String s = names.get(0);   // no cast needed

1class Pair<A, B> {2    final A first;3    final B second;4    Pair(A a, B b) { first = a; second = b; }5}

1static <T extends Comparable<T>> T max(List<T> items) {2    T best = items.get(0);3    for (T x : items) if (x.compareTo(best) > 0) best = x;4    return best;5}

1double sum(List<? extends Number> nums) { ... }    // read numbers2void addInts(List<? super Integer> sink) { ... }   // write integers