じゃんけんあそび3.java

package janken;

import java.util.EnumMap;

public class じゃんけん {

  public enum Result {
    あいこ, 負け, 勝ち
  }

  public enum Hand {
    グー, チョキ, パー
  }

  public interface Step1 {
    Step2 自分の手(Hand myHand);
  }

  public interface Step2 {
    Step3 相手の手(Hand yourHand);
  }

  public interface Step3 {
    Result 勝負();
  }

  private static class Assert {

    public static void assertNotNull(Object value, String message) {
      if (value == null) {
        throw new NullPointerException(message);
      }
    }

    public static void should(boolean condition, String message) {
      if (!condition) {
        throw new AssertionError(message);
      }
    }

    private Assert() {
    }
  }

  private static class ResultTable {

    private EnumMap<Hand, EnumMap<Hand, Result>> table = new EnumMap<>(Hand.class);

    public void put(Hand key1, Hand key2, Result value) {
      Assert.assertNotNull(key1, "key1 is null.");
      Assert.assertNotNull(key2, "key2 is null.");
      Assert.assertNotNull(value, "value is null.");

      EnumMap<Hand, Result> row = table.get(key1);
      if (row == null) {
        row = new EnumMap<>(Hand.class);
        table.put(key1, row);
      }
      row.put(key2, value);
    }

    public Result get(Hand key1, Hand key2) {
      Assert.assertNotNull(key1, "key1 is null.");
      Assert.assertNotNull(key2, "key2 is null.");

      return table.get(key1).get(key2);
    }
  }

  private static class Battle implements Step1, Step2, Step3 {

    private static ResultTable resultTable;

    static {
      resultTable = new ResultTable();

      resultTable.put(Hand.グー, Hand.グー, Result.あいこ);
      resultTable.put(Hand.グー, Hand.チョキ, Result.勝ち);
      resultTable.put(Hand.グー, Hand.パー, Result.負け);

      resultTable.put(Hand.チョキ, Hand.グー, Result.負け);
      resultTable.put(Hand.チョキ, Hand.チョキ, Result.あいこ);
      resultTable.put(Hand.チョキ, Hand.パー, Result.勝ち);

      resultTable.put(Hand.パー, Hand.グー, Result.勝ち);
      resultTable.put(Hand.パー, Hand.チョキ, Result.負け);
      resultTable.put(Hand.パー, Hand.パー, Result.あいこ);
    }

    private Hand myHand;

    private Hand yourHand;

    @Override
    public Step2 自分の手(Hand myHand) {
      Assert.assertNotNull(myHand, "myHand is null.");
      this.myHand = myHand;
      return this;
    }

    @Override
    public Step3 相手の手(Hand yourHand) {
      Assert.assertNotNull(yourHand, "yourHand is null.");
      this.yourHand = yourHand;
      return this;
    }

    @Override
    public Result 勝負() {
      Assert.should(myHand != null, "myHand is null.");
      Assert.should(yourHand != null, "yourHand is null.");

      Result result = resultTable.get(myHand, yourHand);

      Assert.should(result != null, "Result is not found.");
      return result;
    }
  }

  public static Step1 開始() {
    return new Battle();
  }

  private じゃんけん() {
  }
}