C# Online Compiler | .NET Fiddle

using System;

public interface Tool 
{
	void MouseDown();
	void MouseUp();
}

public class SelectionTool: Tool 
{
	public void MouseDown() 
	{
		Console.WriteLine("Selection Icon");
	}
	
	public void MouseUp()
	{
		Console.WriteLine("Draw a dashed rectangle");
	}
}
public class BrushTool: Tool 
{
	public void MouseDown() 
	{
		Console.WriteLine("Brush Icon");
	}
	
	public void MouseUp()
	{
		Console.WriteLine("Draw a line");
	}
}
public class Canvas
{
	public Tool CurrentTool { get; set; }
	
	public void MouseDown()
	{
		CurrentTool.MouseDown();
	}
	
	public void MouseUp()
	{
		CurrentTool.MouseUp();
	}
}

public class Program
{
	public static void Main()
	{
		var canvas = new Canvas();
		canvas.CurrentTool = new SelectionTool();
		canvas.MouseDown();
		canvas.MouseUp();
		
		canvas.CurrentTool = new BrushTool();
		canvas.MouseDown();
		canvas.MouseUp();
		
	}
}