java中声明三角形类,继承图像类,计算三角形的周长和面积,如何编程

class Shape {
void area(){}
void circle(){}
}
public class Triangle extends Shape{
float area(float i,float j){
return i*j/2;
}
float circle(float i,float j,float k){
return i+j+k;
}
public static void main(String[] args){
Triangle tr = new Triangle();
float ar = tr.area(1,2);
System.out.println(ar);
float ci = tr.circle(1,2,3);
System.out.println(ci);
}