Java--枚举(Enum)JDK1.5新特性

港控/mmm° 2023-10-17 11:38 27阅读 0赞

定义枚举类要用关键字enum

所有枚举类都是Enum的子类

枚举类的第一行上必须是枚举项，最后一个枚举项后的分号是可以省略的，但是如果枚举类有其他的东西，这个分号就不能省略。建议不要省略

枚举类可以有构造器，但必须是private的，它默认的也是private的。

枚举类也可以有抽象方法，但是枚举项必须重写该方法

枚举在switch语句中的使用

一、自定义枚举类

1、无参

public class Week {
    	//第一种方法，无参构造
    	public final static Week Mon = new Week();
    	public final static Week TUE = new Week();
    	public final static Week WED = new Week();
    	private Week(){}  //私有构造，不让其他类创建本类
    	@Override
    	public String toString() {
    		return "Week [toString()=" + super.toString() + "]";
    	};       
    }

2、有参

public class Week2 {
    	//第二种方法，有参构造
    	private String name;
    	public final static Week2 Mon = new Week2("星期一");
    	public final static Week2 TUE = new Week2("星期二");
    	public final static Week2 WED = new Week2("星期三");
    	private Week2(String name){
    		this.name = name;
    	}  					//私有构造，不让其他类创建本类
    	
    	public String getName() {
    		return name;
    	}
    
    	@Override
    	public String toString() {
    		return "Week2 [name=" + name + "]";
    	}
    }

3、抽象类，内部类

public abstract class Week3 {
    	//第三种方法抽象类，匿名内部类
    	private String name;
    	public final static Week3 Mon = new Week3("星期一"){
    		@Override
    		public void show() {
    			System.out.println("星期一");
    		}
    	};
    	public final static Week3 TUE = new Week3("星期二"){
    		@Override
    		public void show() {
    			System.out.println("星期二");
    		}
    	};
    	public final static Week3 WED = new Week3("星期三"){
    		@Override
    		public void show() {
    			System.out.println("星期三");
    		}
    	};
    	private Week3(String name){
    		this.name = name;
    	}  					//私有构造，不让其他类创建本类
    
    	public abstract void show();
    }

使用

public class EnumDemo {
    
    	public static void main(String[] args) {
    		demo1();
    		demo2();
    		demo3();
    	}
    
    	private static void demo3() {
    		System.out.println("-------------第三种抽象类，匿名内部类-------------");
    		Week3 mon = Week3.Mon;
    		mon.show();
    	}
    
    	private static void demo2() {
    		System.out.println("-----------------第二种有参构造------------------");
    		Week2 mon = Week2.Mon;
    		Week2 tue = Week2.TUE;
    		Week2 wed = Week2.WED;
    		System.out.println(mon.getName());
    		System.out.println(tue.getName());
    		System.out.println(wed.getName());
    	}
    
    	private static void demo1() {
    		Week mon = Week.Mon;
    		Week tue = Week.TUE;
    		Week wed = Week.WED;
    		System.out.println(mon);
    		System.out.println(tue);
    		System.out.println(wed);
    	}
    }

二、系统枚举类Enum关键字

1、无参

public enum Week {
    	//系统第一种空参
    	MON,TUE,WED;
    }

2、有参

public enum Week2 {
    	//系统第一种空参
    	MON("星期一"),TUE("星期二"),WED("星期三");
    	private String name;
    	private Week2(String name){
    		this.name = name;
    	}
    	public String getName() {
    		return name;
    	}
    }

3、抽象类，内部类

public enum Week3 {
    	//系统第一种空参
    	MON("星期一"){
    		@Override
    		public void show() {
    			System.out.println("星期一");
    		}
    	},TUE("星期二"){
    		@Override
    		public void show() {
    			System.out.println("星期二");
    		}
    	},WED("星期三"){
    		@Override
    		public void show() {
    			System.out.println("星期三");
    		}
    	};
    	private String name;
    	private Week3(String name){
    		this.name = name;
    	}
    	public abstract void show();
    }

使用

public class EnumDemo {
    
    	public static void main(String[] args) {
    		demo1();
    		demo2();
    		demo3();
    		demo4();
    		demo5();
    	}
    
    	private static void demo5() {
    		/*
    		 枚举类的常见方法
    		 	int ordinal()
    		 	int compareTo(E o)
    		 	String name()
    		 	String toString()
    		 	<T> T valueOf(Class<T> type,String name)
    		 	values() 
    		 * */
    		System.out.println("-------------常用方法--------------");
    		Week2 mon = Week2.MON;
    		Week2 tue = Week2.TUE;
    		Week2 wed = Week2.WED;
    		
    		System.out.println(mon.ordinal());    //获取枚举项编号
    		System.out.println(tue.ordinal());
    		System.out.println(wed.ordinal());
    		
    		System.out.println(mon.compareTo(tue));   //比较枚举编号
    		System.out.println(mon.compareTo(wed));
    		
    		System.out.println(mon.name());   //获取实例名称
    		
    		System.out.println(mon.toString());    //调用重写之后的toString()方法
    		
    		Week2 mon1 = Week2.valueOf(Week2.class, "TUE");
    		System.out.println(mon1);
    		
    		System.out.println("--遍历--");
    		Week2[] arr = Week2.values();
    		for (Week2 week2 : arr) {
    			System.out.println(week2);
    		}
    	}
    
    	private static void demo4() {
    		Week3 mon = Week3.MON;
    		switch (mon) {
    		case MON:
    			System.out.println("星期一");
    			break;
    		case TUE:
    			System.out.println("星期二");
    			break;
    		case WED:
    			System.out.println("星期三");
    			break;
    		default:
    			break;
    		}
    	}
    
    	private static void demo3() {
    		System.out.println("-----------系统第三种------------");
    		Week3 mon = Week3.MON;
    		mon.show();
    	}
    
    	private static void demo2() {
    		System.out.println("-----------系统第二种------------");
    		Week2 mon = Week2.MON;
    		System.out.println(mon.getName());
    	}
    
    	public static void demo1() {
    		Week mon = Week.MON;
    		System.out.println(mon);
    	}
    }