[Enhancement] Using Polymorphism to Simplify Object Storage in Canvas

[1chooo]

Since all the objects inherit from Shape, we can use polymorphism to store all the objects in a single shapes list, instead of separating them into shapes and lines.

private List<Shape> shapes = new ArrayList<Shape>();
// private List<Line> lines = new ArrayList<Line>(); // This can be removed

uml-editor/src/Components/Canvas.java

Lines 33 to 34 in 8815efb

	private List<Shape> shapes = new ArrayList<Shape>();
	private List<Line> lines = new ArrayList<Line>();