3、先创建一个Point类，然后定义Trianglele类。在Trianglele类中定义三个Point的实体来表示一个三角形的三个点，再定义一个方法setTri对这三个点进行初始化，然后定义两个方法求三角形的周长、面积。在main()中创建一个对象，求给定三点的三角形的周长、面积。-

3, first create a Point class, and then Trianglele class definition. In Trianglele class definition three Point of the entity to show a triangle of three points, then define a method for the three points setTri initialized, then define two methods for the triangle area, perimeter. In the main () to create an object, for a given at three of the triangle area, perimeter.