以下程序的输出结果为。 abstract class Shape { abstract void display(); } class Circle extends Shape { void display() { System.out.println("Circle"); } } class Rectangle extends Shape { void display() { System.out.println("Rectangle"); } } class Triangle extends Shape { void display() { System.out.println("Triangle"); } } public class AbstractClassDemo{ public static void main(String args[]){ (new Circle()).display(); (new Rectangle()).display(); (new Triangle()).display(); } }