Explain restrictions on using enum in java?\\n

Enumeration (enum) in Java is a datatype which stores a set of constant values. You can use enumerations to store fixed values such as days in a week, months in a year etc.

You can define an enumeration using the keyword enum followed by the name of the enumeration as −

enum Days {    SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY }

Points to keep in mind

You need to keep the following points in mind while declaring an enum −

• It is recommended to write the name of the constants in all capital letters as −

public class EnumerationExample {    enum Days {       SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY    } }

• You can define an enum inside a class.

Example

 Live Demo

public class EnumerationExample {    enum Days {       Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday    }    public static void main(String args[]) {       Days constants[] = Days.values();       System.out.println("Value of constants: ");       for(Days d: constants) {          System.out.println(d);       }    } }

Output

Value of constants: SUNDAY MONDAY TUESDAY WEDNESDAY THURSDAY FRIDAY SATURDAY

• You can have variables and methods inside an enum as −

enum Vehicles {    Activa125, Activa5G, Access125, Vespa, TVSJupiter;    int i; //variable    Vehicles() { //constructor       System.out.println("Constructor of the enumeration");    }    public void enumMethod() {//method       System.out.println("This is a method of enumeration");    } }

But, the first line of the enum must always be the declaration of constants if you write anything else it generates a compile time error −

enum Vehicles { int i; //variable Activa125, Activa5G, Access125, Vespa, TVSJupiter; Vehicles() { //constructor System.out.println("Constructor of the enumeration"); } public void enumMethod() {//method System.out.println("This is a method of enumeration"); } }

Compile time error

Vehicles.java:1: error: <identifier> expected enum Vehicles { ^ Vehicles.java:2: error: ',', '}', or ';' expected int i; //variable ^ Vehicles.java:3: error: <identifiergt; expected Activa125, Activa5G, Access125, Vespa, TVSJupiter; ^ 3 errors

• You cannot define an enum inside a method. If you try to do so it generates a compile time error saying “enum types must not be local”.

public class EnumExample{ public void sample() { enum Vehicles { Activa125, Activa5G, Access125, Vespa, TVSJupiter; } } }

Compile time error

EnumExample.java:3: error: enum types must not be local enum Vehicles { ^ 1 error