Question

Java设计：将下面的抽象类方法改为接口，然后基于接口派生出若干子类，以分别计算三角形、长方形、

和椭圆的面积。小弟对接口不是很熟悉，用抽象类的方法实现了三个形状的计算，求高手将其修改成为接口实现同样的功能。
/*文件1*/
package packageChapter4;

public abstract class PlaneGraphics {
private String shape;

public PlaneGraphics(String shape){
this.shape=shape;
}

public abstract double area();
public void print(){
System.out.println(this.shape+"面积为"+this.area());
}
}

/*文件2*/
package packageChapter4;
public class PlaneGraphics_ex {
public static void main(String[] args) {
PlaneGraphics g=new Rectangle(10,20);
g.print();

g=new Ellipse(10,20);
g.print();

g=new Triangle(10,20);
g.print();
}
}
/*文件3—三角形计算*/
package packageChapter4;
public class Triangle extends PlaneGraphics {
protected double height;
protected double bottom;
protected int p=2;

public Triangle(double height,double bottom){
super("三角形");
this.height=height;
this.bottom=bottom;
}

public double area(){
return height*bottom/p;
}
}
/*文件4——长方形*/
package packageChapter4;
public class Rectangle extends PlaneGraphics {
protected double length;
protected double width;

public Rectangle(double length,double width){
super("长方形");
this.length=length;
this.width=width;
}

public double area(){
return width*length;
}
}

/*文件5——椭圆形*/
package packageChapter4;
public class Ellipse extends PlaneGraphics {
protected double radius_a;
protected double radius_b;

Ellipse(double radius_a,double radius_b){
super("椭圆");
this.radius_a=radius_a;
this.radius_b=radius_b;
}

public double area(){
return Math.PI*radius_a*radius_b;
}
}
额，自己做出来了
贴一个长方形的代码，剩下的都一样修改一下就行
先定义一个接口其中有2个抽象方法，area()和 print()，其中print为输出。字数超出限
package package1接口类方法;

public class Rectangle implements Main {
protected double length;
protected double width;
protected String shape="长方形";

public Rectangle(double length,double width){
this.length=length;
this.width=width;
}

public double area(){
return width*length;
}

public void print(){
System.out.println(this.shape+ "面积为: "+this.area() );
}

public static void main(String[] args){
Rectangle R=new Rectangle(10,20);
R.print();
}
}

Answer 1

接口里面的成员全部是抽象的，而且如果是变量的话就是final类型的，也就是常量。
抽象类里面可以有实现的方法，然后子类继承的话可以重写父类的方法。。