@IntDef的使用（替代枚举）

安卓开发应避免使用Enum（枚举类），因为相比于静态常量Enum会花费两倍以上的内存。使用@IntDef注解来代替枚举是个不错的选择。

添加android注解依赖：

compile 'com.android.support:support-annotations:25.1.0'

使用：

public class MainActivity extends Activity {     //先定义 常量    public static final int SUNDAY = 0;    public static final int MONDAY = 1;    public static final int TUESDAY = 2;    public static final int WEDNESDAY = 3;    public static final int THURSDAY = 4;    public static final int FRIDAY = 5;    public static final int SATURDAY = 6;     //用 @IntDef "包住" 常量；    // @Retention 定义策略    // 声明构造器    @IntDef({SUNDAY, MONDAY,TUESDAY,WEDNESDAY,THURSDAY,FRIDAY,SATURDAY})    @Retention(RetentionPolicy.SOURCE)    public @interface WeekDays {}     @WeekDays int currentDay = SUNDAY;     @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        setCurrentDay(WEDNESDAY);         //声明变量        @WeekDays int today = getCurrentDay();         switch (today){            case SUNDAY:                break;            case MONDAY:                break;            case TUESDAY:                break;            case WEDNESDAY:                break;            case THURSDAY:                break;            case FRIDAY:                break;            case SATURDAY:                break;            default:                break;        }     }     public void setCurrentDay(@WeekDays int currentDay) {        this.currentDay = currentDay;    }     @WeekDays    public int getCurrentDay() {        return currentDay;    }}

public class Toast {    static final String TAG = "Toast";    static final boolean localLOGV = false;    /** @hide */    /*定义部分*/    @IntDef({LENGTH_SHORT, LENGTH_LONG})    @Retention(RetentionPolicy.SOURCE)    public @interface Duration {}    public static final int LENGTH_SHORT = 0;    public static final int LENGTH_LONG = 1;    ...    /*作为类型使用时*/     /**     * Set how long to show the view for.     * @see #LENGTH_SHORT     * @see #LENGTH_LONG     */    public void setDuration(@Duration int duration) {        mDuration = duration;    }    /*做为返回值时*/    /**     * Return the duration.     * @see #setDuration     */    @Duration    public int getDuration() {        return mDuration;    }}

public class MainActivity extends AppCompatActivity{  public static final int STATE_NONE = -1;  public static final int STATE_LOADING = 0;  public static final int STATE_SUCCESS = 1;  public static final int STATE_ERROR = 2;  public static final int STATE_EMPTY = 3;  private @State int state;  public void setState(@State int state){      this.state = state;  }   @State  public int getState() {    return this.state;  }  @IntDef({STATE_EMPTY, STATE_ERROR, STATE_LOADING, STATE_NONE, STATE_SUCCESS})  @Retention(RetentionPolicy.SOURCE)  public @interface State {  }} @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);  }