import java.util.ArrayList;
import java.util.List; 

class Animal {
	private String name;
	public Animal(String pName) {
		name = pName;
	}
	public String getName() {
		return name;
	}
}
class Monkey extends Animal { 
	public Monkey(String pName) {
		super(pName);
	}
	// explicitly tell the compiler that I am overriding a superclass' method
	//	helps detect typo errors
	@Override
	public String toString() {
		return "Monkey:" + getName();
	}
	// there may be other methods here...
}
class Chimp extends Animal { 
	public Chimp(String pName) { super(pName); }
	@Override
	public String toString() {
		return "Chimp:" + getName();
	}
	// there may be other methods here...
}

class Zoo <E> {
	private List<E> animals;
	public Zoo() {
		// Substitutability in action (1) -
		//		Supertype reference to subtype object
		animals = new ArrayList<E>();
	}
	public void addAnimal(E newAnimal) {
		animals.add(newAnimal);
	}	
	@Override
	public String toString() {
		// ArrayList.toString() is invoked at runtime
		return animals.toString();
	}
}