Examples for enum type

The enum keyword is used to declare a new enumeration type. This keyword has been introduced since Java 5. The declaration syntax for an enum type is as follows


enum <name> {

    <enum_constant_1>,

    <enum_constant_2>,

    ...

    <enum_constant_n>

    <enum_constructor>

    // other variables & methods as usual

}







An enum constant can be declared as follows:

<constant_name>[(arguments)] [{class body}]

Rules for enum type







• An enum constant specifies an instance of the enum type.

• An enum constant can be optionally followed by a list of arguments and a class body. The class body is an anonymous class which conforms to rules of anonymous classes and:

• It cannot have any constructor.

• It cannot have any abstract methods.

• Instance methods declared in the class body are only accessible if they override accessible methods declared in the enclosing enum type.

• An enum type cannot be declared abstract or final.

• The Enum<E> is the direct superclass of an enum type.

• An enum type can be only declared inside class level, same as class level or in a separate source file. It cannot be declared inside a method or an inner class.

• An enum type can have constructors, methods and variables just like a regular Java class.

Examples for enum type

A simplest enum type declared inside a class:

class Foo {

    enum DayOfWeek {MON, TUE, WED, THU, FRI, SAT, SUN};

}

A simple enum type declared in a separate Java file:

public enum ErrorCode {

    LOW, HIGH, SEVERE

}

An enum type which contains constructor, method and variable:

enum Day {

    MON(1), TUE(2), WED(3), THU(4), FRI(5), SAT(6), SUN(7);

    Day(int dayNumber) {

        this.dayNumber = dayNumber;

    }

    private int dayNumber;

    public int getDayNumber() {

        return this.dayNumber;

    }

}

An enum type with class body for each enum constant:

enum Priority {

    LOW {

        int getPriorityNumber() {

            return 0;

        }

    },

    NORMAL {

        int getPriorityNumber() {

            return 1;

        }

    },

    HIGH {

        int getPriorityNumber() {

            return 2;

        }

    },

    SEVERE {

        int getPriorityNumber() {

            return 3;

        }

    };

    abstract int getPriorityNumber();

}