Java列舉類

定義列舉類

• 列舉類的使用：

  • 定義：類的物件只有有限個，確定的，稱此類為列舉類
  • 當需要定義一組常量時，使用列舉類會很方便
  • 如果列舉類中只有一個物件，則可以作為單例模式的實現方式

• 定義列舉類

  • 方式一：jdk5.0之前，自定義列舉類

  package www.bh.c.enumtest;
  
  public class Test1 {
      public static void main(String[] args) {
          Season spring = Season.SPRING;
          System.out.println(spring.seasonName);//春天
          System.out.println(spring.getSeasonName());//春天
      }
  
      static class Season {
          //1.宣告物件的屬性：private final修飾
          private final String seasonName;
          private final String seasonDesc;
          //2.建立私有的構造器，並給物件屬性賦值
          private Season(String seasonName,String seasonDesc) {
              this.seasonName=seasonName;
              this.seasonDesc=seasonDesc;
          }
          //提供當前列舉類的多個物件：public static final的
          public static final Season SPRING=new Season("春天","春暖花開");
          public static final Season SUMMER=new Season("夏天","啤酒西瓜");
          public static final Season AUTUMN=new Season("秋天","收穫滿滿");
          public static final Season WINTER=new Season("冬天","火鍋燒烤");
          //其他，獲取列舉類物件的屬性
          public String getSeasonName() {
              return seasonName;
          }
          public String getSeasonDesc() {
              return seasonDesc;
          }
      }
  }
  

  • 方式二：jdk5.0，使用enum關鍵字定義列舉類

使用關鍵字enum定義列舉類

package www.bh.c.enumtest;

public class Test2 {
    public static void main(String[] args) {
        Season summer=Season.SUMMER;
        System.out.println(summer.seasonName);//夏天
        System.out.println(summer.seasonDesc);//夏日炎炎
    }

    enum Season{
        //1.提供當前列舉類的物件，物件之間用","隔開，末尾物件";"結束
        SPRING("春天","春暖花開"),
        SUMMER("夏天","夏日炎炎"),
        AUTUMN("秋天","秋風陣陣"),
        WINTER("冬天","冬暖夏涼");
        //2.宣告物件的屬性：private final修飾
        private final String seasonName;
        private final String seasonDesc;
        //3.建立私有的構造器，並給物件屬性賦值
        Season(String seasonName, String seasonDesc) {
            this.seasonName = seasonName;
            this.seasonDesc = seasonDesc;
        }
        //其他，獲取列舉類物件的屬性
        public String getSeasonName() {
            return seasonName;
        }
        public String getSeasonDesc() {
            return seasonDesc;
        }
    }
}

Enum類的主要方法

• value()方法：返回列舉型別的物件陣列，方便遍歷所有的列舉值

package www.bh.c.enumtest;
import com.sun.jdi.Value;

public class Test2 {
    public static void main(String[] args) {
        Season[] seasons=Season.values();
        for (int i=0;i<seasons.length;i++){
        System.out.println(seasons[i]);//SPRING,SUMMER,AUTUMN,WINTER
        }
    }

• valueOf(String str)：可以把一個字串轉為對應的列舉類物件。要求字串必須是列舉類物件的’“名字”

package www.bh.c.enumtest;
import com.sun.jdi.Value;

public class Test2 {
    public static void main(String[] args) {
        Season spring=Season.valueOf("SPRING");
        System.out.println(spring);//SPRING
    }
}

• toString()：返回當前列舉類物件常量的名稱

package www.bh.c.enumtest;

public class Test2 {
    public static void main(String[] args) {
        Season summer=Season.SUMMER;
        System.out.println(summer.toString());//SUMMER
    }