Painter.java is almost $200$ lines of complicated code. Editing this code would be risky $$ you might break something and have trouble fixing it$.$ Instead, subclass Painter.java $($use starter file UndoRedoPainter.java$).$ When you$$re done, the subclass will only be around $35$ lines, and you will be familiar with those lines because you$$re going to write them, so your job should be much simpler than modifying Painter.java. Also, there$$s zero risk of breaking Painter.java.