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Explain restrictions on using enum in java?
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
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
Updated on: 30-Jul-2019
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