关于多态Polymorphism的简单考题

package exercise.first;

/**
 * About polymorphism:
 * 		1.polymorphism doesn't apply to static methods
 * 		2.polymorphism is only for instance methods
 * @author Zhou-Jingxian
 *
 */
class Singer {
	public static String sing(){
		return "la";
	}
	
	public String sing2(){
		return "s2";
	}
}

public class Tenor extends Singer{
	public static String sing(){
		return "fa";
	}
	
	public String sing2(){
		return "t2";
	}
	
	public static void main(String []args){
		Tenor t = new Tenor();
		Singer s = new Tenor();
		System.out.println(t.sing() + " "+ s.sing());
		System.out.println(t.sing2() + " "+ s.sing2());
	}
}

 

 

Polymorphism (Objective 5.2)

❑ Polymorphism means "many forms."

❑ A reference variable is always of a single, unchangeable type, but it can refer to a subtype object.

❑ A single object can be referred to by reference variables of many different types —as long as they are the same type or a supertype of the object.

❑ The reference variable's type (not the object's type), determines which methods can be called!

❑ Polymorphic method invocations apply only to overridden instance methods.