Java enum keyword example

In Java, 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}]

Some rules for enum type in Java:

• • 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:

1. 1. • 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.

Java enum type examples:

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();
}

See all keywords in Java.

Other Recommended Tutorials:

• 9 Rules about Constructors in Java
• 12 Rules and Examples About Inheritance in Java
• 12 Rules of Overriding in Java You Should Know
• 10 Java Core Best Practices Every Java Programmer Should Know
• Understand Interfaces in Java
• Understand how variables are passed in Java
• Understand encapsulation in Java

About the Author:

Nam Ha Minh is certified Java programmer (SCJP and SCWCD). He began programming with Java back in the days of Java 1.4 and has been passionate about it ever since. You can connect with him on Facebook and watch his Java videos on YouTube.