interface Strategy { void exec(); }

class Context {
  private Strategy s;

  public Context(Strategy s) { this.s = s; }
  public void exec() { s.exec(); }
}

class StrategyA implements Strategy {
  public void exec() {
    System.out.println("StrategyA");
  }
}

class StrategyB implements Strategy {
  public void exec() {
    System.out.println("StrategyB");
  }
}

class Main {
  public static void main(String[] args) {
    new Context(new StrategyA()).exec();
    new Context(new StrategyB()).exec();
  }
}