Visitor and strategy look very much similar as they deal with encapsulating complex logic from data. We can say visitor is more general form of strategy.
In strategy we have one context or a single logical data on which multiple algorithms operate. In the previous questions we have explained the fundamentals of strategy and visitor. So let’s understand the same by using examples which we have understood previously. In strategy we have a single context and multiple algorithms work on it. Figure ‘Strategy’ shows how we have a one data context and multiple algorithm work on it.
Figure: – Strategy
In visitor we have multiple contexts and for every context we have an algorithm. If you remember the visitor example we had written parsing logic for every data context i.e. customer, address and phones object.
Figure: – Visitor
So in short strategy is a special kind of visitor. In strategy we have one data context and multiple algorithms while in visitor for every data context we have one algorithm associated. The basic criteria of choosing whether to implement strategy or visitor depends on the relationship between context and algorithm. If there is one context and multiple algorithms then we go for strategy. If we have multiple contexts and multiple algorithms then we implement visitor algorithm.