4-3Java中的抽象類課后題，大家?guī)兔纯矗?/h1>

public?abstract?class?Shape{
????public?abstract?void?Circle();
????public?abstract?void?Area();
}
public?class?Rectangle?extends?Shape{
????int?a=2;
????int?b=3;
????public?void?Circle();
????public?void?Area();
????System.out.println("矩形的周長="+2*(a+b));
????System.out.println("矩形的面積="+a*b);
}
public?class?Circle?extends?Shape{
????double?r=3.15;
????double?P=3.14;
????public?void?Circle();
????public?void?Area();
????System.out.println("圓形的周長="+2Pr);
????System.out.println("圓形的面積="+Pr*r);
}
????public?static?void?main(Spring[]?args){
????????Shape?i=new?Rectangle();
????????i.Circle();
????????i.Area();
????????Shape?j=new?Circle();
????????j.Circle();
????????j.Area();
????}