java在一个类里如何引用自己定义的接口类里面的借口

package javaapplication26;


public class getinterface {
    interface getPerimeter
    {
        double PI=3.14;
        double getLength();
    }
    interface getArea
    {
        double getArea();
    }
}

以上是我定义的接口类，我想在Circle里面实现getLength和getArea接口，应该如何实现？

public interface ICircle{
    double getPerimeter();    
    double getArea();
}
public class Circle implements ICircle{

    private double r = 3.7;
    @Override
    public double getPerimeter() {
        // TODO Auto-generated method stub
        double PI=3.14;
        return PI;
    }

    @Override
    public double getArea() {
        // TODO Auto-generated method stub
        double PI = 3.14;
        double area = PI * r * r;
        return area;
    }
}