Design pattern - Strategy and Bridge (Overlap in design)

Question

Today my dilemma arises from trying to understand why there is overlapping in how Strategy and Bridge Pattern can be implemented.

Here is Bridge Pattern (Abstracting an implementation from an abstraction)

// Shapes object structure will not be concerned how they draw themselves
public abstract class Shape {
   protected DrawAPI drawAPI;

   protected Shape(DrawAPI drawAPI){
     this.drawAPI = drawAPI;
   }
   // This could also be put in the subcla
   public void draw() {
     drawAPI.drawCircle(radius,x,y);
   }
}

Now here is Strategy Pattern - a class behavior or its algorithm can be changed at run time. A Calculator will delegate its operations to a strategy

public class Calculator{
  private Strategy strategy;

  public Calculator(Strategy strategy){
    this.strategy = strategy;
  }

  public int executeStrategy(int num1, int num2){
     return strategy.doOperation(num1, num2);
  }
}

Both of these patterns involve discarding strategy objects which encapsulate functionality. Please help with a clear difference between the Bridge Pattern (Structural) and Strategy Pattern (Behavioral). Another confusion I am having is that they are under different umbrellas of knowledge.

Answer 1

In your example I see a little of overlapping between these two patterns.

In the first case, Bridge pattern is used when we need to decouple an abstraction from its implementation so that the two can vary independently. That's all, you're just abstracting the implementation.

In the second case Strategy a class behaviour can be changed at run time. Which also means that into to a concrete Strategy class you could also have implemented a Bridge pattern, maybe you're using a class and want to decuple it.