枚举类的介绍

Posted 2020-09-03

• 枚举类，即对象为可穷举的类
  
• JDK 1.5 新增的 enum 关键字用于定义枚举类，在这之前，需要自定义枚举类
• 若枚举只有一个成员(对象)，则可以作为一种单例模式的实现方式——单例（单子）设计模式（Singleton）

自定义枚举类：

public class TestSeason {
	public static void main(String[] args) {
		Season spring = Season.SPRING;
		Season summer = Season.SUMMER;
		Season autumn = Season.AUTUMN;
		Season winter = Season.WINTER;
		System.out.println(spring);// Season [seasonName=春天]
		System.out.println(summer);// Season [seasonName=夏天]
		System.out.println(autumn);// Season [seasonName=秋天]
		System.out.println(winter);// Season [seasonName=冬天]
	}
}
class Season {
	// 1.提供以 private final 修饰的类属性
	private final String seasonName;
	
	// 2.在以 private 修饰的构造器中初始化类属性
	private Season(String seasonName) {
		this.seasonName = seasonName;
	}
	
	// 3.提供公共的方法来调用属性
	public String getSeasonName() {
		return this.seasonName;
	}
	
	// 4.创建以 public static final 修饰的该枚举类的对象
	public static final Season SPRING = new Season("春天");
	public static final Season SUMMER = new Season("夏天");
	public static final Season AUTUMN = new Season("秋天");
	public static final Season WINTER = new Season("冬天");
	
	@Override
	public String toString() {
		return "Season [seasonName=" + seasonName + "]";
	}
}

使用 enum 关键字定义枚举类及其特性：

public class TestSeason {
	public static void main(String[] args) {
		Season spring = Season.SPRING;
		Season summer = Season.SUMMER;
		Season autumn = Season.AUTUMN;
		Season winter = Season.WINTER;
		System.out.println(spring);// Season [seasonName=春天]
		System.out.println(summer);// Season [seasonName=夏天]
		System.out.println(autumn);// Season [seasonName=秋天]
		System.out.println(winter);// Season [seasonName=冬天]
		
		// 枚举类常用的方法
		// 1.以数组的形式返回所有枚举类的对象：values();
		Season[] seasons = Season.values();
		for (Season s : seasons) {
			System.out.println(s);
		} // Season [seasonName=春天]
			// Season [seasonName=夏天]
			// Season [seasonName=秋天]
			// Season [seasonName=冬天]
		
		// 2.返回以指定字符串为对象名的对象（要求形参 str 是枚举对象的名字，
		// 否则报IllegalArgumentException）：valueOf(String str);
		String str = "SPRING";
		System.out.println(Season.valueOf(str).getSeasonName());// 春天
		// 接口的特殊实现
		Season.valueOf(str).show();// 春暖花开
	}
}
interface Info {
	void show();
}
enum Season implements Info {
	// 与自定义枚举类对比：对象声明要放最前面，重复的部分删除，对象之间以逗号分隔
	// 枚举类实现接口，可以让不同对象以不同的方式实现接口中的抽象方法（也可以让类
    // 实现，各对象共享）
	SPRING("春天") {
		public void show() {
			System.out.println("春暖花开");
		}
	},
	SUMMER("夏天") {
		public void show() {
			System.out.println("夏日炎炎");
		}
	},
	AUTUMN("秋天") {
		public void show() {
			System.out.println("秋高气爽");
		}
	},
	WINTER("冬天") {
		public void show() {
			System.out.println("白雪皑皑");
		}
	};
	
	private final String seasonName;
	
	private Season(String seasonName) {
		this.seasonName = seasonName;
	}
	
	public String getSeasonName() {
		return this.seasonName;
	}
	
	@Override
	public String toString() {
		return "Season [seasonName=" + seasonName + "]";
	}
}