用java将圆的周率定义为常量，编写一个求圆面积的方法，调用此方法来求圆的面积．

public class Math {
public static double yuan = 3.14;
public double area(double i){
double s = 0;
s = i*yuan;
return s;
}
public static void main(String[] args) {
Math m = new Math();
double area = m.area(10);
System.out.println(area);
}
}
这就算出半径为10的面积了。

public static void main(String[] args){
double r=1.5;//半径
mianJi(r);
}

public static double mianJi(double r){
double mianji=Math.PI*r*r;
}

final double pai=3.14;//定义常量

class Circle
{
final double PI=3.14;
double r;

Circle()
{
r=0;
}
Circle(double r)
{
this.r=r;
}
double area()
{
return Math.PI.r*r;
}
}

public class test
{
public static void main(String[] args)
{
double r=Double.parseDouble(args[0]);
Circle p=new Circle(r);
System.out.println