抽象类的使用（java）

抽象类的使用

import java.util.Scanner;

public abstract class Shape {
	public abstract double area();
	public abstract double length();

}

public class Rect extends Shape {
	int a;
	int b;
	
	public Rect(int a, int b) {
		this.a = a;
		this.b = b;
	}

	@Override
	public double area() {
		// TODO Auto-generated method stub
		return a*b;
	}

	@Override
	public double length() {
		// TODO Auto-generated method stub
		return 2*(a+b);
	}

}

public class Tri extends Shape {
	int a, b, c;
	
	public Tri(int a, int b, int c) {
		this.a = a;
		this.b = b;
		this.c = c;
	}

	@Override
	public double area() {
		double p = (1.0/2)*(a+b+c);
		return (Math.sqrt(p*(p-a)*(p-b)*(p-c)));
	}

	@Override
	public double length() {
		// TODO Auto-generated method stub
		return a+b+c;
	}

}

public class Main {  
	 public static void main(String[] args) {  
		 Scanner reader = new Scanner(System.in); 
		 Shape aa = new Rect(10,20);
		 Shape bb = new Tri(3, 4, 5);
		 System.out.println(aa.area());
		 System.out.println(aa.length());
		 System.out.println(bb.area());
		 System.out.println(bb.length());
	 }
}