CSC/ECE 517 Fall 2010/ch3 3h PW

The Strategy pattern in static and dynamic languages

What is the Strategy Pattern

The main purpose of the strategy pattern is to separate out an object and how it behaves into two different classes. The first advantage for doing this is so that if an object can have different behaviors then it is easy to manage them in their own classes. Secondly, if a certain type of behavior need to be changed, it only need to be changed in that behavior class rather than in multiple classes if there were multiple objects that had this behavior.

How to Implement in a Static Language

Example

Java Code

interface Action {
    void perform();
}
 
// Implements the algorithm using the strategy interface
class Dribble implements Action {
 
    public void perform() {
        System.out.println("Player is dribbling");
    }
}
 
class Pass implements Action {
 
     public void perform() {
        System.out.println("Player is passing");
    }
}
 
class Shoot implements Action {
 
    public void perform() {
        System.out.println("Player is shooting");
    }    
}
 
// Configured with a ConcreteStrategy object and maintains a reference to a Strategy object
class BasketBallPlayer {
 
    private Action action;
 
    // Constructor
    public BasketBallPlayer(Action action) {
        this.action = action;
    }
 
    public void perform() {
        action.perform();
    }
}
//BasketBallPlayerExample test application
 
class BasketBallPlayerExample {
 
    public static void main(String[] args) {
 
        BasketBallPlayer bballPlayer;
 
        // Three contexts following different strategies
        bballPlayer = new BasketBallPlayer(new Dribble());
        bballPlayer.perform();
 
        bballPlayer = new BasketBallPlayer(new Pass());
        bballPlayer.perform();
 
        bballPlayer = new BasketBallPlayer(new Shoot());
        bballPlayer.perform();
    }
}

How to Implement in a Dynamic Language

Examples

Ruby code