Decorator Pattern

Decorator Patten is a Structural Patter. i.e It talks about how to structure your classes.

Decorator pattern just decorates the pre-existing class. So that we do not have the change the class that we are trying to decorate.

interface Shape{
    public void draw();
}

abstract class ShapeDecorator implements Shape{
    protected Shape targetObject;
    public ShapeDecorator(Shape targetToDecorate){
         targetObject = targetToDecorate;
    }

   @Override
   public void onDraw(){
        targetObject.draw();
   }
}


So now we can have RedShapeDecorator or BlueShapeDecorator concrete classes which will override onDraw(), call super and do more stuff to it, to decorate.

class RedShapeDecorator extends ShapeDecorator{
    public RedShareDecorator(Share target){
       super(target);
   }

   @Override
   public void draw(){
       super.draw();
       target.setBorderColor("red");
   }
}

Client will use it like.


Shape shape = new Circle();
Shape  redDecor = new RedShapeDecorator(shape);
redDecor.draw();