CODEWITHSUNDEEP
javadesign-patterns
blue-sky
blue-sky

Reputation: 53816

Design pattern for filtering objects

I have a List of objects which will be filtered.

This filtering will consist of at least 3 rules.

So for example : 

public class Filtering {

List<MyObject> myObjectList;

List<MyObject> filterStep1(List<MyObject> myObjectList){

    for(Myobject myobj : myObjectList){
        if(isCriteriaSatisified){
            continue
        }
        else {
            removeThisObjectFromList
        }
    }
}


List<MyObject> filterStep2(List<MyObject> myObjectList){

    for(Myobject myobj : myObjectList){
        if(isCriteriaSatisified){
            continue
        }
        else {
            removeThisObjectFromList
        }
    }
}

}

I like this approach as it is simple, self contained and can see very easily what is trying to be achieved.

But perhaps there is a design pattern I should be using instead ?

The "Chain of Responsibility" pattern is something I'm considering where filterStep1 & filterStep2 in above code would be refactored into a seperate hander.

Upvotes: 5

Views: 2506

Answers (2)

Andrejs
Andrejs

Reputation: 27687

One option using Java 8 streams:

myObjects.stream().filter( this::isCriteriaSatisified ).filter( this::anotherCriteria )

Assuming you have a method boolean isCriteriaSatisified(myObj) in your class. You can then collect that stream into another List.

Upvotes: 2

chrylis -cautiouslyoptimistic-
chrylis -cautiouslyoptimistic-

Reputation: 77177

This is the "pipes and filters" pattern, and while your implementation is okay, it's better not to hardcode the filtering logic in methods. Instead, write a Predicate<MyObject> for each of your boolean conditions (either the one built into Java 8 or the one from Guava). This is much easier to test and can easily be applied to existing clean APIs, such as the Streams API or Guava's collection views.

Upvotes: 5

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