strategy

Strategy pattern

In Strategy pattern, we create objects which represent various strategies and a Context object whose behavior varies as per its strategy object. The Strategy object changes the executing algorithm of the context object.

Real word API examples

java.util.Comparator in kind of strategy interface. This is an implementation of some comparison strategy:

class Player {
    int rank; points;

    Player(int rank, int points){
        this.rank = rank;
        this.points = points;
    }
    
    int getRank() { return rank; }
    int getPoints() { return getPoint; }
}

One way to sort a collection of players is:

Collections.sort(players, (p1, p2) -> p1.rank - p2.rank);

The lambda here represents a strategy: (p1, p2) -> p1.rank - p2.rank. Another strategy can be: (p1, p2) -> p1.points - p2.points or Comparator.comparing(Player::getPoints).

Internally Collections.sort(...) will invoke player_i.comapre(player_j) defined by the lambda or anonymous function.