Delegates, Why? [duplicate]

Answer 1

Using your example of Operations, imagine a calculator which has several buttons. You could create a class for your button like this

class CalcButton extends Button {
   Operations myOp;
   public CalcButton(Operations op) {
      this.myOp=op; 
   }
   public void OnClick(Event e) {
      setA( this.myOp(getA(), getB()) ); // perform the operation
   }
}

and then when you create buttons, you could create each with a different operation

CalcButton addButton = new CalcButton(new Operations(f.multiply));

This is better for several reasons. You don't replicate the code in the buttons, they are generic. You could have multiple buttons that all have the same operation, for example on different panels or menus. You could change the operation associated with a button on the fly.