Adv' Topic 6'3, 13'7 Enum

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Adv. Topic 6.3, 13.7 - Enum
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Enumerated Types

• How do we represent a finite set of values?
• Set of nucleotides, amino acids
• Marriage status
• Automaton types
• So far we arbitrarily give values
• AutomatonTypes were classes with a String value
• MARRIED 1 SINGLE 0
• A 0 C 1 G 2 T 3

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Use enum

• Problem with those approaches is that there are
  no constraints ? bugs
• base 5
• marriageStatus 2
• Solution - Enumerated Types enum
• Special class in Java 1.5.0
• Enumerated types are used to represent cases
  where there are a finite number of possible values

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• public enum FilingStatus SINGLE, MARRIED
• ----
• Usage
• FilingStatus status FilingStatus.SINGLE
• if(status FilingStatus.SINGLE)...

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Example

• public class TaxReturn
• public enum FilingStatus SINGLE, MARRIED
• private FilingStatus status
• public TaxReturn(double inIncome, FileStatus
  inStatus)

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Outside class access

• Can be treated as a class field
• TaxReturn tr new TaxReturn(income,
  TaxReturn.FilingStatus.SINGLE)
• public enum Base A, C, G, T

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AT 13.7

• Enumeration is just a special class
• No constructor. Why?
• All enumerated classes extend Enum
• Inherit a toString() and clone() method
• toString()
• Just returns the objects name as a String
• FilingStatus.SINGLE.toString() ? SINGLE
• clone()
• Just returns the object, no copy is created

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Adding methods

• Can add methods/constructors to an enumerated
  type
• All instances must be created in the class though
• public enum CoinType
• private double value
• PENNY(0.01), NICKEL(0.05), DIME(0.1),
  QUARTER(0.25)
• CoinType(double aValue)
• value aValue
• public double getValue()
• return value

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• Have four instances
• CoinType.PENNY, CoinType.NICKEL, etc
• All have a value associated with them now
• CoinType.PENNY.getValue()
• Not the same as Coin class
• Coin class could create multiple objects(many
  pennies in piggy bank)
• CoinType only describes types of coins

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AutomatonType revisited

• AutomatonType was a more generic enumerated type
• We made constructor private ? no new objects
  could be created
• All public constants
• All have a string value associated
• How would our AutomatonType class look with enum?
• What could we add to store arrays?

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• public enum AutomatonType GLIDER, LONER, EMPTY,
  SPIRAL
• Does our game of life class have to change?