Creating a GUI Theme System in Java

These days, having dark mode in your application is all the rage (take the snazzy color switch on this site, for example {not bad for someone who's color blind.. at least, so I'm told!}).

Using the Bridge Pattern with GUI components allows you to easily switch out between any number of themes and styles, giving you and your users the power to tailor an app to their liking!

Theme Implementor:

public interface Theme
{
   String Background();
   String Foreground();
   String LineColor();
   String FontColor();
   String AltFontColor();
}

UIObject Abstraction:

public abstract class UIObject
{
   protected Theme theme;

   public UIObject(Theme theme)
   {
       this.theme = theme;
   }

   public abstract void Draw();
}

Dark and Light Themes:

//Theme 1: LightMode:
public class LightMode implements Theme
{
   public String Background() { return "#ffffff"; }
   public String Foreground() { return "#aaaaaa"; }
   public String LineColor() { return "#0c60cd"; }
   public String FontColor() { return "#222222"; }
   public String AltFontColor() { return "#000000"; }
}

//Theme 2: Dark Mode:
public class DarkMode implements Theme
{
   public String Background() { return "#111111"; }
   public String Foreground() { return "#2d2d2d"; }
   public String LineColor() { return "#0c60cd"; }
   public String FontColor() { return "#dfdfdf"; }
   public String AltFontColor() { return "#efefef"; }
}

UIButton and UIGraph Components:

//UI Object 1: a button:
public class UIButton extends UIObject
{
   public UIButton(Theme theme)
   {
       super(theme);
   }

   public void Draw() 
   {
       System.out.println("Drawing a button on the screen.");
       System.out.println("\tText Color: " + this.theme.FontColor());
       System.out.println("\tButton Color: " + this.theme.Background());
       System.out.println("\tHighlight Text Color: " + this.theme.AltFontColor());
   }
}

//UI Object 2: a graph:
public class UIGraph extends UIObject
{
   public UIGraph(Theme theme)
   {
       super(theme);
   }

   public void Draw()
   {
       System.out.println("Drawing a graph on the screen.");
       System.out.println("\tMain Text Color: " + this.theme.FontColor());
       System.out.println("\tLine Color: " + this.theme.LineColor());
       System.out.println("\tAxis Text Color: " + this.theme.AltFontColor());
       System.out.println("\tGraph Background Color: " + this.theme.Foreground());
   }
}

Bridge Pattern Demo:

public class Solution
{
   public static void main(String[] args)
   {
       // Create the themes:
       Theme light = new LightMode();
       Theme dark = new DarkMode();

       // Create the UI Objects:
       UIObject button = new UIButton(light);
       UIObject graph = new UIGraph(dark);

       // Draw the objects:
       button.Draw();
       graph.Draw();
   }
}

//Output:
/*
   Drawing a button on the screen.
       Text Color: #222222
       Button Color: #ffffff
       Highlight Text Color: #000000
       
   Drawing a graph on the screen.
       Main Text Color: #dfdfdf
       Line Color: #0c60cd
       Axis Text Color: #efefef
       Graph Background Color: #2d2d2d
*/