Inheritance - Java Concepts - page 652

A DVANCED T OPIC 10.7: Enumerated Types Revisited

In Advanced Topic 5.3 , we introduced the concept of an enumerated type: a type
with a finite number of values. An example is

public enum FilingStatus { SINGLE, MARRIED }

In Java, enumerated types are classes with special properties. They have a finite
number of instances, namely the objects defined inside the braces. For example,
there are exactly two objects of the FilingStatus class:
FilingStatus.SINGLE and FilingStatus.MARRIED . Since
FilingStatus has no public constructor, it is impossible to construct
additional objects.

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Enumeration classes extend the Enum class, from which they inherit toString
and clone methods. The toString method returns a string that equals the
object's name. For example, FilingStatus.SINGLE.toString() returns
Ȓ SINGLE ȓ. The clone method returns the given object without making a copy.
After all, it should not be possible to generate new objects of an enumeration
class.

The Enum class inherits the equals method from its superclass, Object .
Thus, two enumeration constants are only considered equal when they are
identical.

You can add your own methods and constructors to an enumeration class, for
example

public enum CoinType
{
PENNY(0.01), NICKEL(0.05), DIME(0.1),
QUARTER(0.25);
CoinType(double aValue) { value = aValue; }
public double getValue() { return value; }
private double value;
}

This CoinType class has exactly four instances: CoinType.PENNY ,
CoinType.NICKEL , CoinType.DIME , and CoinType.QUARTER . If you