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  • Java Enumeration

    ref: http://www.studytonight.com/java/enumerations

    Enumerations

    Enumeration was added to Java language in JDK5. Enumeration means a list is named constant. In java, enumeration

    defines a class type. An Enumeration can have constructors, methods and instance variables. It is created using

    enum keyword. Each enumeration constant is public, static and final by default.

    Even though enumeration defines a class type and have constructors, you do not instantiate an enum using new. 

    Enumeration variables are used and declared in much a same way as you do in primitive variables

    How to Define and Use an Enumeration

    enum Subject           //Enumeration defined
    {
     Java, Cpp, C, Dbms
    }


    1. Java, Cpp, C, Dbms are called enumeration constants. They are public,static, final by default

    2. variable of enumeration can be defined directly without new keyword

    Subject sub

    3. variable of enumeration type can have only enumeration constants as value

      sub = Subject.java;


    Values( ) and ValueOf( ) method

    All the enumerations has values() and valueOf() methods inthem. 

    values() :method returns an array of enum-type containing all the enumeration constants in it.

      public static enum-type[] values()

    valueOf(): method is used to return enumeration constant whose value is equal to the string passed in as argument while calling this method

      public static enum-type valueOf(String str)

    Points to remember about Enumerations

    1. Enumeration are of class type, and have all capabilities taht a java class has

    2. Enumerations can have constructors, instance variables, methods and can even implement interfaces

    3. Enumerations are not instantiated using new 

    4. All Enumerations by default inherite java.lang.Enum class

    enum Student
    {
     John(11), Bella(10), Sam(13), Viraaj(9);
     private int age;                   //age of students
     int getage { return age; }
     public Student(int age)
     {
      this.age= age;
     }
    }
    
    class EnumDemo
    {
     public static void main( String args[] )
     {
      Student S;
      System.out.println("Age of Viraaj is " +Student.Viraaj.getage()+ "years");
     }
    }

    Output :
    Age of Viraaj is 9 years






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  • 原文地址:https://www.cnblogs.com/morningdew/p/5619728.html
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