Android使用@IntDef和枚举enum限制元素取值范围的比较

枚举的作用就是
定义此元素允许的常量

1.使用@IntDef限制元素的取值范围

package com.wong.ex;

import androidx.annotation.IntDef;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

public class MainActivity extends AppCompatActivity { //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;

	// 定义＠WeekDays注解 @IntDef({SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY}) @Retention(RetentionPolicy.SOURCE) public @interface WeekDays { }

	// 声明变量，限制变量的取值范围 @WeekDays int currentDay = SUNDAY; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); // 声明变量，限制变量的取值范围 @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; } setCurrentDay(SUNDAY) } // 添加@WeekDays注解，限制传入值的范围 public void setCurrentDay(@WeekDays int currentDay) { this.currentDay = currentDay; }

	// 添加@WeekDays注解，限制返回值的范围 @WeekDays public int getCurrentDay() { return currentDay; }
}

  

 

  
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虽然getCurrentDay()方法使用了＠WeekDays注解限制它返回的值的范围，但是从实践来看，限制的作用有时会失效，如：

	@WeekDays public int getCurrentDay() { return 888; }

  

 

  
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上面的代码＠WeekDays起作用了，因为888不是所期望的取值。但是也仅仅是提示而已，告诉你必须是那些上面定义的那些常量。编译依然能通过，程序照样运行。下面这种，干脆就不提示了：

	@WeekDays public int getCurrentDay() { return currentDay+888; }

  

 

  
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setCurrentDay()方法也是有同样的问题。
总的来说@IntDef的限制，感觉没有那么严格。

2.使用枚举来限制元素的取值范围

public class MainActivity extends AppCompatActivity { //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; private enum WeekDays {SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY}; WeekDays currentDay = WeekDays.SUNDAY; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); //声明变量 WeekDays 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; } setCurrentDay(WeekDays.SUNDAY); } public void setCurrentDay(WeekDays currentDay) { this.currentDay = currentDay; } public WeekDays getCurrentDay() { return currentDay; }
}

  

 

  
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使用枚举可以非常有效的限制元素的取值范围。

3.总结

虽然枚举可以很有效的限制元素的取值范围，但是这是以牺牲性能为前提的。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。所以呢，如果追求性能的话，建议使用@IntDef来限制元素的取值范围。

文章来源: blog.csdn.net，作者：WongKyunban，版权归原作者所有，如需转载，请联系作者。

原文链接：blog.csdn.net/weixin_40763897/article/details/107211105