abstract class Strategy {
  abstract public void algorithmInterface();
}

public class ConcreteStrategyA extends Strategy {
  public ConcreteStrategyA() {
  }
  public void algorithmInterface() {
    System.out.println("ConcreteStrategyA algorithmInterface()メソッド");
  }
}

public class ConcreteStrategyB extends Strategy {
  public ConcreteStrategyB() {
  }
  public void algorithmInterface() {
    System.out.println("ConcreteStrategyB algorithmInterface()メソッド");
  }
}

public class ConcreteStrategyC extends Strategy {
  public ConcreteStrategyC() {
  }
  public void algorithmInterface() {
    System.out.println("ConcreteStrategyC algorithmInterface()メソッド");
  }
}

public class Context {
  Strategy strategy;

  public Context(Strategy strategy) {
    this.strategy = strategy;
  }

  public void contextInterface() {

    strategy.algorithmInterface();
  }
}

public class Client {
  public static void main(String[] args) {
    Context a = new Context(new ConcreteStrategyA());
    a.contextInterface();

    Context b = new Context(new ConcreteStrategyB());
    b.contextInterface();

    Context c = new Context(new ConcreteStrategyC());
    c.contextInterface();
  }
}

C:\JavaHello\Strategy>java Client
ConcreteStrategyA algorithmInterface()メソッド
ConcreteStrategyB algorithmInterface()メソッド
ConcreteStrategyC algorithmInterface()メソッド

C:\JavaHello\Strategy>