file names and class names in java

1class Triangle {
2            int x, y;
3            void printArea()
4            {
5                        System.out.println("Area of triangle is: " + x * y / 2);
6            }
7}
8class Demo {
9            public static void main(String args[])
10            {
11                        Triangle t = new Triangle();
12                        t.x = 10;
13                        t.y = 13;
14                        t.printArea();
15            }
16}