"We simply cannot afford another wildcards" - Joshua Bloch

GenericWildcards.java

Enum<E extends Enum<E>> { ... }

<T extends Object & Comparable<? super T>> T Collections.max(Collection<? extends T>) { ... }

public <V extends Wrapper<? extends Comparable<T>>>
  Comparator<V> comparator() { ... }

error: equalTo(Box<capture of ?>) in Box<capture of ?> cannot be applied to (Box<capture of ?>)
  equal = unknownBox.equalTo(unknownBox)

Arrays.asList(String.class, Integer.class) // Warning!