【java】 向上转型的运用

应用 ：求面积

1，抽象类  Geometry .

public abstract class Geometry {
    
    public abstract double getArea();
    
}

2，矩形 Rect

public class Rect extends Geometry{
    
    double a,b;
    
    Rect(double a,double b){
        this.a = a;
        this.b = b;
    }
    
    @Override
    public double getArea() {
        return a*b;
    }
    
}

3，圆形 Circle

public class Circle extends Geometry{
    double r;
    
    public Circle(double r) {
        this.r = r;
    }
    
    @Override
    public double getArea() {
        // TODO Auto-generated method stub
        return 3.14*r*r;
    }
    
}

4，  数组存模 ， 使用抽象方法 。  求面积和   （注入灵魂） 

public class TotalArea {
    
    double area(Geometry ...p) {
    
        double sum = 0;
        
        for (int i = 0; i < p.length; i++) {
            
            sum += p[i].getArea();
            
        }
        
        return sum;    
    }

}

5 ， 主类 Main

public class Main {
    
    public static void main(String[] args) {
        
        TotalArea t = new TotalArea();
        
        double area = t.area(new Rect(2, 3),new Circle(5.2),new Circle(12));
        
        System.out.printf("面积和: 
",area);
        
    }
    
}