There is not a drawTriangle method neither in Graphics nor Graphics2D. You need to do it by yourself. You can draw three lines using the drawLine
method or use one these methods:
These methods work with polygons. You may change the prefix draw
to fill
when you want to fill the polygon defined by the point set. I inserted the documentation links. Take a look to learn how to use them.
There is the GeneralPath class too. It can be used with Graphics2D, which is capable to draw Shapes. Take a look: