枚举方式的线程安全的单例

public enum Color {
    blue, red, yellow
}

public final class voctrals.study.whatisspring.test.Color extends java.lang.Enum<voctrals.study.whatisspring.test.Color> {
  public static final voctrals.study.whatisspring.test.Color blue;
  public static final voctrals.study.whatisspring.test.Color red;
  public static final voctrals.study.whatisspring.test.Color yellow;
  public static voctrals.study.whatisspring.test.Color[] values(); // jdk给加上的
  public static voctrals.study.whatisspring.test.Color valueOf(java.lang.String); // jdk给加上的
  public int getValue();
  static {};
}

    /**
     * prevent default deserialization
     */
    private void readObject(ObjectInputStream in) throws IOException,
        ClassNotFoundException {
        throw new InvalidObjectException("can‘t deserialize enum");
    }

    private void readObjectNoData() throws ObjectStreamException {
        throw new InvalidObjectException("can‘t deserialize enum");
    }

public class BeanContainer {

    public static BeanContainer getInstance() {
        return ContainerHolder.HOLDER.instance;
    }

    private enum ContainerHolder {
        HOLDER;
        private BeanContainer instance;

        ContainerHolder() {
            instance = new BeanContainer();
        }
    }
}