用注解提供代码的静态检查

Android 包android.support.annotation包提供了诸如 @IntDef 和 @StringDef 等注解，可以让AS, Lint 提供静态代码检查功能

用注解型枚举代替普通静态常量和枚举

原因：

1. 枚举销毁的内存是普通静态常量的两倍
2. 普通静态常量不能提供检查

枚举：

public class Demo{
   enum Status{
     IDLE,PROCESSING,DONE,CANCELLED
    }
  Status status;
  void setStatus(Status status){
    this.status = status;
  }
}

普通静态常量：

public class Demo{
  public static final int IDLE = 0;
  public static final int CANCELLED = 1;
  
  public int status;
  //这里的参数不能提供检查,可以传入任意int
  public setStatus(int status) {
    this.status = status;
  }
}

枚举型注解：

 public static class Status {
        public static final int IDLE = 0;
        public static final int CANCELLED = 1;
   
    @Retention(RetentionPolicy.SOURCE)
        @IntDef({Status.IDLE, Status.CANCELLED})
        public @interface StatusTypeDef {
        }
   
        public int status;
   
        @StatusTypeDef
        public int getStatus() {
            return status;
        }

        public void setStatus(@StatusTypeDef int status) {
            this.status = status;
        }
    }

其他利用注解增强代码的静态检查

dependencies { compile 'com.android.support:support-annotations:23.3.0'}

official Android annotations guide

annotations	description
@Nullable	Can be null.
@NonNull	Cannot be null.
@StringRes	References a R.string resource.
@DrawableRes	References a Drawable resource.
@ColorRes	References a Color resource.
@Interpolator	Res References a Interpolator resource.
@AnyRes	References any type of R. resource.
@UiThread	Should only be called on the UI thread

例子：

- public View onCreateView(@NonNull Context context);
- public abstract void setTitle(@StringRes int resId);
- public void setAlpha(@IntRange(from=0,to=255) int alpha) {}
- public void setAlpha(@FloatRange(from=0.0, to=1.0) float alpha){}