Understanding wildcards in Java generics
List<String> a = new ArrayList<String>();
a.add("foo");

// b is a List of anything
List<?> b = a;

// retrieve the first element
Object c = b.get(0);
// This is legal, because we can guarantee
// that the return type "?" is a subtype of Object

// Add an Integer to b.
b.add(new Integer (1));

Object c = b.get(0);

public Foo findAFooThatILike(Collection<? extends Foo> foos);

public Foo findAFooThatILike(Collection<Foo> foos);