跟王老师学枚举（一）为何须要枚举

跟王老师学枚举（一）：为何须要枚举

主讲教师：王少华   QQ群号：483773664

1、需求

一些方法在运行时，它须要的数据不能任意的，而必须是必定范围内的值。好比，有如下需求：学生的考试成绩只能分为A B C D E五个等级，不能是其余的等级

2、实现

（一）第一种方式：字符串

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public class Student {      private String name;    //姓名      private String grade;   //成绩：A B C D E      public String getName() {          return name;      }      public void setName(String name) {          this .name = name;      }      public String getGrade() {          return grade;      }      public void setGrade(String grade) {          //若是赋值不在这些等级内，则抛出异常          if (!grade.matches( "[ABCDE]" )){              throw new RuntimeException( "不支持此参数！" );          }          this .grade = grade;      } }

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public class StudentTest {      public static void main(String[] args) {          Student student = new Student();          student.setGrade( "X" );      } }

（二）第二种方式:常量

把这个类的全部可能实例都使用 public static final 修饰

须要private 将构造器隐藏起来

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public class Grade {      public static final  Grade A= new Grade( "A" );      public static final  Grade B= new Grade( "B" );      public static final  Grade C= new Grade( "C" );      public static final  Grade D= new Grade( "D" );      public static final  Grade E= new Grade( "E" );      private String value;      private Grade(String value){          this .value = value;      }      public String getValue() {          return value;      } }

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public class Student {      private String name;    //姓名      private Grade grade;    //成绩：A B C D E      public String getName() {          return name;      }      public void setName(String name) {          this .name = name;      }      public Grade getGrade() {          return grade;      }      public void setGrade(Grade grade) {          this .grade = grade;      } }

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public class StudentTest {      public static void main(String[] args) {          Student student = new Student();          student.setGrade(Grade.A);      } }

来自为知笔记(Wiz)