【程式語言】JAVA的第十堂課 ｜物件導向程式設計(抽象類別)

ch11.java

class ch11 {
	public static void main(String[] aa) {
	Coin c1=new Coin(1);
	Coin c5=new Coin(5);
	Coin c10=new Coin(10);
   
	c1.show();
    c5.show();
    c10.show();
	System.out.println(c10.toString());
	c1.show_area();
 }
}

Circle.java

abstract class Circle{
	protected double r;
	protected static double pi = 3.14;
	Circle() {	
	}
	Circle (double a) {
		r = a;
	} 
	abstract void show();
	abstract void show_area();
	
	void setR(int a) {
		r = a;
	}
}

Coin.java

class Coin extends Circle{
	private int value;
	Coin(int v){
		value = v;
		if (v == 1) {
			setR(1);
		}
		else if (v == 5) {
			setR(5);
		}
		else if (v == 10) {
			setR(10);
		}
		else if (v == 50) {
			setR(50);
		}
	}
	
	void show() {
		System.out.println("R=" + r);
		System.out.println("value=" + value);
	}
	void show_area() {
		System.out.println("Area=" + value*value*pi);
	}
	
	//override
	public String toString() {
		String str = "toString is called!";
		return str;
	}

}

Result: