我为何要在Android中使用枚举（enum），如何使用？

灰太狼 2021-09-11 07:46 697阅读 0赞

上篇博客讲了安卓官方并不推荐使用枚举和枚举的利弊，那么问题来了，除去代码简洁外我们为何要在Android中使用枚举（enum）？

毕竟：Enum 需要占用较大的内存，如果对内存敏感，请尽量少使用 Enum，换用做静态常量。

我们先来看两段代码：

public class Main {
        //静态定义星期start
        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;
        //静态定义星期end
    
        private int currentDay = SUNDAY;//currentday可以被设置成任何整数值
    
        public static void main(String[] args) {
            // TODO Auto-generated method stub
            Main obj = new Main();
            obj.setCurrentDay(WEDNESDAY);
    
            int today = obj.getCurrentDay();
    
            switch (today) {
            case SUNDAY:
                System.out.println("Today is SUNDAY");
                break;
            case MONDAY:
                System.out.println("Today is MONDAY");
                break;
            case TUESDAY:
                System.out.println("Today is TUESDAY");
                break;
            case WEDNESDAY:
                System.out.println("Today is WEDNESDAY");
                break;
            case THURSDAY:
                System.out.println("Today is THURSDAY");
                break;
            case FRIDAY:
                System.out.println("Today is FRIDAY");
                break;
            case SATURDAY:
                System.out.println("Today is SATURDAY");
                break;
    
            default:
                break;
            }
        }
    
        public void setCurrentDay(int currentDay) {
            this.currentDay = currentDay;
        }
    
        public int getCurrentDay() {
            return currentDay;
        }
    }

这段代码的问题是currentday可以被设置成任何整数值，例如：

obj.setCurrentDay(100);

实际上currentday取值范围只能是0-6，当我们的值超出这个范围时编译器不会提示任何错误，我们的switch/case语句就是去了它的作用，所以Java给我们提供了枚举Enum这个解决方案。

上面的代码写成枚举的方案如下：

public class Main {
    
        public enum WeekDays {
            SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY
        }
    
        private WeekDays currentDay = WeekDays.SUNDAY;
    
        public static void main(String[] args) {
            // TODO Auto-generated method stub
            Main obj = new Main();
            obj.setCurrentDay(WeekDays.WEDNESDAY);
    
            WeekDays today = obj.getCurrentDay();
    
            switch (today) {
            case SUNDAY:
                System.out.println("Today is SUNDAY");
                break;
            case MONDAY:
                System.out.println("Today is MONDAY");
                break;
            case TUESDAY:
                System.out.println("Today is TUESDAY");
                break;
            case WEDNESDAY:
                System.out.println("Today is WEDNESDAY");
                break;
            case THURSDAY:
                System.out.println("Today is THURSDAY");
                break;
            case FRIDAY:
                System.out.println("Today is FRIDAY");
                break;
            case SATURDAY:
                System.out.println("Today is SATURDAY");
                break;
    
            default:
                break;
            }
        }
    
        public void setCurrentDay(WeekDays currentDay) {
            this.currentDay = currentDay;
        }
    
        public WeekDays getCurrentDay() {
            return currentDay;
        }
    }

**这样我们的取值类型就绝对是安全的，currentDay 的取值范围是固定的，不存在无效取值了。这是一个伟大进步，这个时候就要使用枚举。**

内存用量也并非那么地可怕，枚举带来的编码的便捷，代码可读性的提升也是很大的利好。