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The filter pattern enables you to define filters for your objects.

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Suppose that you work with the same hierarchy of objects that we've seen in the previous tutorial,

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a store with purses and bags.

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If your goal is to filter out some objects based on their color or on any other available attribute,

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then the filter pattern is the way to go.

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The pattern is characterized by having a filter interface with classes that implement that interface,

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which will allow us to do and or in various filters based on the attributes of the objects that are

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filtered.

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Let's have a look how this looks in the code.

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We will be working with the same code as we did in the previous tutorials, so we have the same abstract

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class here called Store, and for the sake of simplicity, I just deleted the back class and I left

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only the purse.

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So here we can see that the code is untouched.

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We have the same constructor that accepts an object of type color and the same method that will return

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the color to us.

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Apart from this, we have the filter interface here that has only one method midfielder which will return

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a list of persons to us and also it accepts as an argument on the software.

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Of course, we should have had a store after class here, but for the sake of simplicity, I just left

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it with letters and some classes also that are implementing this this interface.

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So we have the glue filter that will filter all the purses that are blue.

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So it will return a list to us that will contain only blue purses and an end filter that will perform

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the logical end operation.

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So basically it will apply to filters on and the final list will contain all the elements that were

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filtered out by the two filters and another filter, which will perform as the name suggests, the ore

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operation and this filter basically will return the elements that are in one list after filtering once

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and not in the second list.

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So this is actually the ore operation that is performed here.

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So let's see this in action.

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Let's and class.

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So here we define three blue verses and one redBus.

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So essentially, if we are and also we add them into one single list and essentially if we apply a blue

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filter on them, then we should see only the blue passes and the red should be filtered out.

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So let's see this in action.

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So as you can see, instead of having all the four line zero, the four, of course, is printed here,

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we have only three because we created only three blue versus the other one is red.

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So, as you can see, this is working as expected.

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So you can have plenty, plenty of criteria.

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This is this as I said, this design pattern is also called criteria pattern.

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So you can have as much criteria as you want and many, many classes that will implement the filter

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interface here.

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So but this is just an overly simplified example just to see how this should be implemented.

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That's it for the filter pattern.

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Join me in the next tutorial where we are going to discuss about a composite pattern.

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So see you in the next story on.