【Java基础】枚举类的方法及应用

如何实现让一个类有固定个数的对象

手动封装构造方法（private） → 创建静态对象 → final修饰静态对象，使其成为常量

class Season { //枚举类
	public final static Season SPRING = new Season();
	public final static Season SUMMER = new Season();
	public final static Season SUTUMN = new Season();
	public final static Season WINTER = new Season();
	private Season() {}
	public void show() {
		System.out.println("hello");
	}
}
class Demo7 {
	public static void main(String[] args) {
		Season chunji = Season.SPRING;
		chunji.show();
	}
}

enum

从 JDK1.5 开始

enum Season {
    SPRING,SUMMER,AUTUMN,WINTER  //枚举项，枚举常量
}
class Demo7{
	public static void main(String[] args) {
		Season chunji = Season.SPRING;
		chunji.show();
	}
}

反编译后，跟上一个步骤类似
在这里插入图片描述
枚举类的本质就是一个类，被final修饰了，不能有子类，继承了java.lang.Enum

枚举类方法

int ordinal()
返回枚举项的编号，每个枚举项都有一个编号，编号从0开始

enum Week{
	MONDAY,TUESDAY,WEDNESDAY,THURSDAY,FRIDAY,SATURDAY,SUNDAY
}
class Demo10{
	public static void main(String[] args){
	     Week[] weeks={Week.MONDAY,Week.TUESDAY,Week.WEDNESDAY,Week.THURSDAY,Week.FRIDAY,Week.SATURDAY,Week.SUNDAY};
		 System.out.println(weeks[0].ordinal());//0
		 System.out.println(weeks[2].ordinal());//2
		 System.out.println(weeks[6].ordinal());//6

int compareTo(E o)
比较枚举项的大小，比较的是编号

System.out.println(weeks[6].compareTo(weeks[2]));//4
System.out.println(weeks[2].compareTo(weeks[4]));//-2
System.out.println(weeks[2].compareTo(weeks[2]));//0

String name()
返回枚举常量的名称，与其枚举声明中声明的完全相同

System.out.println(weeks[6].name());//SUNDAY
System.out.println(weeks[4].name());//FRIDAY

String toString()
返回声明中包含的此枚举常量的名称

System.out.println(weeks[6].toString());//SUNDAY
System.out.println(weeks[4].toString());//FRIDAY

static <T extends Enum> T value0f(Class enumType, String name)
返回具有指定名称的指定枚举类型的枚举常量
```
Week obj = Enum.valueOf(Week.class,"MONDAY"); //MONDAY
```

public static Week[] values()
得到所有枚举项的数组

Week[] arr = Week.values();
for(Week wk:arr)
	System.out.println(wk);//MONDAY TUESDAY WEDNESDAY ……

public static Week valueOf(java.lang.String);
返回具有指定名称的指定枚举类型的枚举常量
```
Week xingqi = Week.valueOf("MONDAY");
System.out.println(xingqi);//MONDAY
```

定义属性

enum中构造方法默认被private修饰

enum Season{
	SPRING("春季"),SUMMER("夏季"),AUTUMN("秋季"),WINTER("冬季");  
	private String desc;
	Season(){}  //默认就是private
	Season(String desc){//默认就是private
		this.desc=desc;
	}
	public String getDesc(){
		return desc;
	}
	public String toString(){
		return desc;
	} 
}
class Demo11{
	public static void main(String[] args){
		Season ss = Season.SUMMER;
		System.out.println(ss);
	}
}

定义方法

静态、非静态方法

enum Season{
    ……………………
	public static void show()
	{
		System.out.println("Hello");
	}
    public void fun()
	{
		System.out.println("fun");
	}
}
class  Demo12 
{
	public static void main(String[] args) 
	{
		Season xiaji=Season.SUMMER;
		xiaji.show();
		xiaji.fun();
	}
}

抽象方法

含有抽象方法前的枚举类前不用写abstract，在每个枚举项里都必须重写抽象方法

enum Season{
	SPRING("春季"){
		public void show(){
			System.out.println("春季");
		}
	},SUMMER("夏季"){
		public void show(){
			System.out.println("夏季");
		}
	},AUTUMN("秋季"){
		public void show(){
			System.out.println("秋季");
		}
	},WINTER("冬季"){
		public void show(){
			System.out.println("冬季");
		}
	};  
	……………………
	public abstract void show();
}
class Demo13 
{
	public static void main(String[] args){
		Season.WINTER.show();
	}
}

实现接口

interface inter{
	void ff();
}
enum Season implements inter{
    SPRING("春季"),SUMMER("夏季"),AUTUMN("秋季"),WINTER("冬季");  
	………………
	public void ff(){
		System.out.println("ok");
	}
}
class Demo14{
	public static void main(String[] args){
		Season.AUTUMN.ff();
		Enum  jijie=Season.WINTER;  //多态
		Object obj=Season.WINTER;
	}
}

练习

定义一个Person类，有姓名和性别属性，性别定义成枚举

enum Gender{
	MALE("男"),FEMALE("女");
	private String desc;
	Gender(){}
	Gender(String desc){
		this.desc=desc;
	}
	public String toString(){
		return desc;
	}
}
class Person{
	private String name;
	private Gender sex;
	Person(){}
	Person(String name,Gender sex){
		this.name=name;
		this.sex=sex;
	}
	public String toString(){
		return name+","+sex;
	}
}
class Demo15 {
	public static void main(String[] args) {
		Person ren=new Person("赵四",Gender.MALE);
		System.out.println(ren);//赵四，男
	}
}