Enumerated Types Define a new data type and list all possible values: enum Season {winter, spring,...

Enumerated Types• Define a new data type and list all possible values:

enum Season {winter, spring, summer, fall}

• Then the new type can be used to declare variables

Season time;

• And then the variable can be assigned a value:

time = Season.fall;

• The only values this variable can be assigned are the ones from the enum definition

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Why would we want to use enums?


//********************************************************************// IceCream.java Author: Lewis/Loftus//// Demonstrates the use of enumerated types.//********************************************************************

public class IceCream{ enum Flavor {vanilla, chocolate, strawberry, fudgeRipple, coffee, rockyRoad, mintChocolateChip, cookieDough}

//----------------------------------------------------------------- // Creates and uses variables of the Flavor type. //----------------------------------------------------------------- public static void main (String[] args) { Flavor cone1, cone2, cone3;

cone1 = Flavor.rockyRoad; cone2 = Flavor.chocolate;

System.out.println ("cone1 value: " + cone1); System.out.println ("cone1 ordinal: " + cone1.ordinal()); System.out.println ("cone1 name: " + cone1.name());

continued


continued

System.out.println (); System.out.println ("cone2 value: " + cone2); System.out.println ("cone2 ordinal: " + cone2.ordinal()); System.out.println ("cone2 name: " + cone2.name());

cone3 = cone1;

System.out.println (); System.out.println ("cone3 value: " + cone3); System.out.println ("cone3 ordinal: " + cone3.ordinal()); System.out.println ("cone3 name: " + cone3.name()); }}


continued

System.out.println (); System.out.println ("cone2 value: " + cone2); System.out.println ("cone2 ordinal: " + cone2.ordinal()); System.out.println ("cone2 name: " + cone2.name());

cone3 = cone1;

System.out.println (); System.out.println ("cone3 value: " + cone3); System.out.println ("cone3 ordinal: " + cone3.ordinal()); System.out.println ("cone3 name: " + cone3.name()); }}

Outputcone1 value: rockyRoadcone1 ordinal: 5cone1 name: rockyRoadcone2 value: chocolatecone2 ordinal: 1cone2 name: chocolatecone3 value: rockyRoadcone3 ordinal: 5cone3 name: rockyRoad

A basic enumerated type

public enum CommandWord{ // A value for each command word, // plus one for unrecognised commands. GO, QUIT, HELP, UNKNOWN;}

• Each name represents an object of the enumerated type, e.g. CommandWord.HELP. • Enumerated objects are not created directly by the programmer.

Another enumerated typepublic enum CommandWord{ // A value for each command word, // plus one for unrecognised commands. GO(“go”), QUIT(“quit”), HELP(“help”), UNKNOWN(“unknown); private String commandWord;

// Initialize the command word CommandWord (String commandword) { this. commandWord = commandWord; } public String toString() { return commandWord; }}

.

Enumerated Types• An enumerated type definition can be more interesting

than a simple list of values

• Because they are like classes, we can add additional instance data and methods

• We can define an enum constructor as well

• Each value listed for the enumerated type calls the constructor

• See Season.java • See SeasonTester.java



//********************************************************************// Season.java Author: Lewis/Loftus//// Enumerates the values for Season.//********************************************************************

public enum Season{ winter ("December through February"), spring ("March through May"), summer ("June through August"), fall ("September through November");

private String span;

//----------------------------------------------------------------- // Constructor: Sets up each value with an associated string. //----------------------------------------------------------------- Season (String months) { span = months; }

//----------------------------------------------------------------- // Returns the span message for this value. //----------------------------------------------------------------- public String getSpan() { return span; }


//********************************************************************// SeasonTester.java Author: Lewis/Loftus//// Demonstrates the use of a full enumerated type.//********************************************************************

public class SeasonTester{ //----------------------------------------------------------------- // Iterates through the values of the Season enumerated type. //----------------------------------------------------------------- public static void main (String[] args) { for (Season time : Season.values()) System.out.println (time + "\t" + time.getSpan()); }}

Enumerated Types• Every enumerated type contains a static method called values that returns a list of all possible values for that type

• The list returned from values can be processed using a for-each loop

• An enumerated type cannot be instantiated outside of its own definition

• A carefully designed enumerated type provides a versatile and type-safe mechanism for managing data


Enumerated Types Define a new data type and list all possible values: enum Season {winter, spring,...

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