Behavioral Patterns : Strategy

Properties:

-          Separates implementation from algorithm (strategy).  

-          The same class can be used with different algorithms.

Implementation:

-          Strategy creates an abstraction for different algorithms.

-          ConcreteStrategy implements strategy interface for a specific algorithm.

-          Context object uses strategy object to do its job. Its behaviour depends on the concrete strategy implementation.

Java Standard Library Implementations:

-          java.util.Collections.html#sort(java.util.List, java.util.Comparator) uses Comparator as strategy.

Example Usage:

   

List<Person> winners = ...

// Strategy instance

Comparator<Person> comparator = new Comparator<Person>() {

    public int compare(Person o1, Person o2) {

        return o1.getAge() - o2.getAge();

    }};

   

// Set strategy

Collections.sort(winners, comparator);