Enumeration
• Skandal att detta inte fanns i Java 1.0
• Uppräkningsbar typ
Enumeration
• Man räknar upp alla värden som typen ska ha
• Tidigare innan detta dök upp i java användes heltalskonstanter
ofta för uppgifter där man nu använder enums
Jan Erik Moström
Johan Eliasson
Innan enum
public class Navigate {
final public static
final public static
final public static
final public static
Med enum
int
int
int
int
public class Navigate {
public enum Direction { NORTH, SOUTH, EAST, WEST };
NORTH = 1;
SOUTH = 2;
EAST = 3;
WEST = 4;
void go( Direction dir ) {
switch( dir ){
case NORTH:
// ...
break;
case SOUTH:
// ...
break;
case WEST:
// ...
break;
case EAST:
// ...
break;
}
}
void go( int dir ) {
switch( dir ){
case NORTH:
// ...
break;
case SOUTH:
// ...
break;
case WEST:
// ...
break;
case EAST:
// ...
break;
default:
// ...
}
}
}
}
Johan Eliasson
Johan Eliasson
package cards;
public class Card {
public enum Rank { DEUCE, THREE, FOUR, FIVE, SIX, SEVEN, EIGHT,
NINE, TEN, JACK, QUEEN, KING, ACE }
public enum Suit { CLUBS, DIAMONS, HEARTS, SPADES }
Kortleksexempel
import java.util.Scanner;
import cards.Deck;
import cards.Card;
public class CardDemo
{
public static void main( String[] args ) {
Scanner in=new Scanner(System.in);
int numHands = in.nextInt();
int handSize = in.nextInt();
Deck d = new Deck();
for( int i = 0; i < numHands; i++ ){
System.out.println( d.getHand( handSize) );
}
}
}
private final Rank rankValue;
private final Suit suitValue;
Card( Rank rankValue, Suit suitValue ) {
this.rankValue = rankValue;
this.suitValue = suitValue;
}
public Rank rank( ) {
return rankValue;
}
public Suit suit( ) {
return suitValue;
}
4
5
[QUEEN of CLUBS, SIX of DIAMONS, JACK of HEARTS, FOUR of SPADES, FIVE of HEARTS]
[EIGHT of DIAMONS, JACK of DIAMONS, FIVE of CLUBS, NINE of SPADES, THREE of CLUBS]
[ACE of HEARTS, SEVEN of HEARTS, TEN of HEARTS, THREE of HEARTS, TEN of DIAMONS]
[KING of SPADES, NINE of DIAMONS, FOUR of CLUBS, SEVEN of DIAMONS, DEUCE of DIAMONS]
Johan Eliasson
public String toString( ) {
return rankValue + " of " + suitValue;
}
}
Johan Eliasson
package cards;
import java.util.List;
import java.util.ArrayList;
package cards;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class Deck
{
private List<Card> myDeck;
public class Hand {
private List<Card> hand;
public Hand( List<Card> content ) {
hand = content;
}
public Deck( ) {
myDeck = new ArrayList<Card>( );
for( Card.Suit suit : Card.Suit.values( ) ){
for( Card.Rank rank : Card.Rank.values( ) ){
myDeck.add( new Card( rank, suit ) );
}
}
Collections.shuffle( myDeck );
}
public String toString( ) {
return hand.toString();
}
public Hand getHand( int nrOfCards ) {
List<Card> handCards = myDeck.subList( 0, nrOfCards );
Hand hand = new Hand( new ArrayList<Card>(handCards) );
handCards.clear();
return hand;
}
}
}
Johan Eliasson
public enum
{
MERCURY
VENUS
EARTH
MARS
JUPITER
SATURN
URANUS
NEPTUNE
PLUTO
Inte en klass utan en enum!!!
Planet
(3.303e+23,
(4.869e+24,
(5.976e+24,
(6.421e+23,
(1.9e+27,
(5.688e+26,
(8.686e+25,
(1.024e+26,
(1.27e+22,
Johan Eliasson
2.4397e6),
6.0518e6),
6.37814e6),
3.3972e6),
7.1492e7),
6.0268e7),
2.5559e7),
2.4746e7),
1.137e6);
public class WeightDemo {
public static void main(String[] args) {
Scanner in=new Scanner(System.in);
System.out.println(“Enter your earth weight”);
double earthWeight = in.nextDouble();
double mass = earthWeight/Planet.EARTH.surfaceGravity();
for( Planet p : Planet.values() )
System.out.println("Your weight on ” + p + “ is " +
p.surfaceWeight(mass));
}
private final double mass;
// in kilograms
private final double radius; // in meters
Planet(double mass, double radius)
{
this.mass = mass;
this.radius = radius;
}
public double mass()
{ return mass; }
public double radius() { return radius; }
}
// universal gravitational constant (m3 kg-1 s-2)
public static final double G = 6.67300E-11;
public double surfaceGravity()
{
return G * mass / (radius * radius);
}
public double surfaceWeight(double otherMass)
{
return otherMass * surfaceGravity();
}
}
Johan Eliasson
Johan Eliasson
