import java.util.*;

public class ChainDemo {

  static interface Command {
    void execute(Map<String, Object> ctx);
  }

  static class Chain {
    private List<Command> commands = new ArrayList<Command>();

    public void addCommand(Command cmd) {
      commands.add(cmd);
    }

    public void execute() {
      Map<String, Object> ctx = new HashMap<String, Object>();

      for (Command cmd : commands) {
        cmd.execute(ctx);
      }
    }

  }

  public static void main(String[] args) {
    Chain chain = new Chain();
    chain.addCommand(new Command() {
      public void execute(Map<String, Object> ctx) {
        // Perform some calc here
        ctx.put("result1", 1234);
      }
    });
    chain.addCommand(new Command() {
      public void execute(Map<String, Object> ctx) {
        int res = (Integer) ctx.get("result1");
        ctx.put("result2", res * 2);
      }
    });
    chain.addCommand(new Command() {
      public void execute(Map<String, Object> ctx) {
        System.err.println("Results: ");
        for (String key : ctx.keySet()) {
          System.err.println("\t" + key + ": " + ctx.get(key));
        }
      }
    });
    chain.execute();
  }
}