[java5新特性]枚举

超、凢脫俗 2021-12-01 13:18 266阅读 0赞

**JDK5之前**

//自定义枚举类 JDK5之前
    //对象有限个且作为静态常量出现
    class Season{ 
        //1.声明Season对象的属性:private final修饰
        private final String seasonName;
        private final String seasonDesc;
    
        //2.私有化类的构造器
        private Season(String seasonName,String seasonDesc){ 
            this.seasonName=seasonName;
            this.seasonDesc=seasonDesc;
        }
    
        //3.提供当前枚举类的多个对象
        public static final Season SPRING = new Season("春天","春暖花开");
        public static final Season SUMMER = new Season("夏天","夏日炎炎");
        public static final Season AUTUMN = new Season("秋天","秋高气爽");
        public static final Season WINTER = new Season("冬天","冰天雪地");
    
        //getXxx()
        public String getSeasonName() { 
            return seasonName;
        }
    
        public String getSeasonDesc() { 
            return seasonDesc;
        }
        
    }

**JDK5新增enum关键字**

enum Season { 
        //1.提供当前枚举类的对象，多个对象之间用,隔开，末尾用;结束
        SPRING("春天","春暖花开"),
        SUMMER("夏天","夏日炎炎"),
        AUTUMN("秋天","秋高气爽"),
        WINTER("冬天","冰天雪地");
    
        //2.声明Season对象的属性
        private final String seasonName;
        private final String seasonDesc;
    
        //3.私有化构造器
        Season(String seasonName, String seasonDesc) { 
            this.seasonName = seasonName;
            this.seasonDesc = seasonDesc;
        }
    
        //4.getXxx()
        public String getSeasonName() { 
            return seasonName;
        }
    
        public String getSeasonDesc() { 
            return seasonDesc;
        }
    }

**enum在Thread中的应用**  
Thread类中使用枚举类表示线程的状态

public enum State { 
            NEW,
            RUNNABLE,
            BLOCKED,
            WAITING,
            TIMED_WAITING,
            TERMINATED;
        }

**java.lang.Enum的常用方法**  
values()：返回枚举类型的对象数组，该方法可以很方便地遍历所有地枚举值  
valueOf(String str):可以把一个字符串转为对应的枚举类对象。要求字符串必须是枚举类对象的名字，否则报非法参数异常  
toString():返回枚举类对象变量的名称

public class Demo { 
        public static void main(String[] args) { 
            //values()
            Thread.State[] values = Thread.State.values();
            System.out.println(Arrays.toString(values));//[NEW, RUNNABLE, BLOCKED, WAITING, TIMED_WAITING, TERMINATED]
            //valueOf(String str)
            Thread.State state = Thread.State.valueOf("NEW");
            //toString()
            System.out.println(state);//NEW
        }
    }