Zoo.java

package zoo;

class Animal {}

class Lion extends Animal {}

class Cage<T extends Animal> {
	void add(T animal) { System.out.println("Adding animal..."); }

	public static void main(String... args) {
		Cage<? extends Animal> animals = null;
		Cage<Lion> lions = null;
		animals = lions;
		animals.add(new Lion()); //ERROR
	}
}

/*
The method add(capture#2-of ? extends Animal) in the type Cage is not applicable to for the arguments (Lion)
*/