大家来看看一下，到底什么有关问题，说说吧

大家来看看一下，到底什么问题，说说吧
import java.util.*;

 abstract class Figure
{
  protected String shape;

  protected Figure(String shape)
  {
  this.shape = shape;
  }

  protected Figure()
  {
  this("未知");
  }

  public abstract double area();

  public abstract double perimeter();

  public void print()
  {
  System.out.println("一个" + this.shape + "," + this.toString() + ",周长为"
  + this.perimeter() + ",面积为" + this.area());
  }
}

class Triangle extends Figure
{
  protected double a;
  protected double b;
  protected double c;

  public Triangle(double a, double b, double c)
  {
  super("三角形");
  this.a = a;
  this.b = b;
  this.c = c;
  }

  public Triangle()
  {
  this(0, 0, 0);
  }

  public String toString()
  {
  return "a边长" + this.a + ",b边长" + this.b + ",c边长" + this.c;
  }

  public double area()
  {
  return (Math.sqrt((a + b + c) / 2.0) * (((a + b + c) / 2.0) - a)
  * (((a + b + c) / 2.0) - b) * (((a + b + c) / 2.0) - c));
  }

  public double perimeter()
  {
  return (a + b + c);
  }
}

到这里是正确的，编译通过，但是确实主函数
不知道以下抽象类的对象引用子类实例是否正确



class ClosedFigure_ex
{
public static void main(String args[])
{ClosedFigure g=new Triangle(3,4,5);
g.print();
}
}


------解决方案--------------------

探讨

我想请问的是这个程序如何在JDK中运行啊，交一些方法。