计算几何图形的面积

Shape:

Shape：

package Area;
/**
 * 求面積
 * @author Administrator
 *
 */
public abstract class Shape {
public String getName(){
    return this.getClass().getName();//獲得類名稱
}
public abstract double getArea();

}

Circle:

package Area;

public class Circle extends Shape{
private double radius;
public Circle(){
}
public Circle(double radius){
    this.radius=radius;
}
public double getArea(){//主要是抽象的實現
    return Math.PI*Math.pow(radius,2);
}
}

Triangle:

package Area;

public class Triangle extends Shape{
private double x;
private double y;
public Triangle(){
    
}
public double getArea(){
    return (x*y)/2;
}
public Triangle(double x,double y){
    this.x=x;
    this.y=y;
}
}

Test:

package Area;

public class Test {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Circle circle = new Circle(1);
        System.out.println("the shape is:" + circle.getName());
        System.out.println("the Area: "+circle.getArea());
        
        Shape tri=new Triangle(1,1);
        System.out.println("the shape is:" +tri.getName());
        System.out.println("the shape is:" + tri.getArea());
    }

}

 focus :

在抽象类中，可以定义抽象方法，用abstrat修饰，包含抽象方法的类一定是抽象类，而抽象类不一定包含抽象方法

抽象类是不能直接被实例化的，如果要获得该类的实例，可以使用静态方法传剪其类对象，