[英]How To Implement A Method Signature That Will Return a Concrete Type of an Enum?
[英]How to implement certain method for enum type
我是编程和Java的新手,目前正在学习枚举类型。
我创建了一个枚举类型的Card
,它将每张卡的值存储在一副纸牌中,例如2 = 2、3 = 3 ... Ace =11。每张图片卡具有相同的值10。
我正在尝试实现方法getPrevious()
,该方法将返回列表中的上一个枚举值。 例如,如果在SIX
上调用了该方法,则它将返回FIVE
,而在TWO
被调用时,将返回ACE
。 但是,我正在努力寻找一种方法来做到这一点。
在下面,您可以看到我所编写的当前代码,有关如何实现方法getPrevious()
任何帮助或提示都将非常有用。
public class EnumPractice {
public enum Card {
TWO(2), THREE(3), FOUR(4), FIVE(5), SIX(6), SEVEN(7), EIGHT(8),
NINE(9), TEN(10), JACK(10), QUEEN(10), KING(10), ACE(11), ;
private int value;
private Card card;
Card(int value){
this.value = value;
}
public int getValue(){
return value;
}
public String toString(){
return "The value of this card is: " + value;
}
}
public static void main(String[] args) {
System.out.println(Card.ACE.getValue());
}
}
您的getPrevious()
方法如下所示
public enum Card {
TWO(2), THREE(3), FOUR(4), FIVE(5), SIX(6), SEVEN(7), EIGHT(8),
NINE(9), TEN(10), JACK(10), QUEEN(10), KING(10), ACE(11);
private int value;
Card(int value) {
this.value = value;
}
public int getValue() {
return value;
}
public Card getPrevious() {
int previous = ordinal() - 1;
if (previous < 0 ) { // if negative, then we have to go to the last element
previous += values().length;
}
return Card.values()[previous];
}
}
这是您的getPrevious()
实现
import java.util.Arrays;
public class EnumPractice {
public enum Card {
TWO(2), THREE(3), FOUR(4), FIVE(5), SIX(6), SEVEN(7), EIGHT(8),
NINE(9), TEN(10), JACK(10), QUEEN(10), KING(10), ACE(11), ;
private int value;
private Card card;
Card(int value){
this.value = value;
}
public int getValue(){
return value;
}
public String toString(){
return "The value of this card is: " + value;
}
public Card getPrevious() {
int pos = ordinal();
if (pos == 0)
return ACE;
return values()[pos - 1];
}
}
public static void main(String[] args) {
System.out.println(Card.THREE.getPrevious());
System.out.println(Card.TWO.getPrevious());
}
}
上面的程序输出是
The value of this card is: 2
The value of this card is: 11
其他方法可能是保留对先前卡的引用。 您可以在所有卡都在静态块中创建后进行设置,例如:
public enum Card {
TWO(2), THREE(3), FOUR(4), FIVE(5), SIX(6), SEVEN(7), EIGHT(8),
NINE(9), TEN(10), JACK(10), QUEEN(10), KING(10), ACE(11);
private int value;
private Card previous;
static{
//lets set previous element for cards
//we will iterate starting from TWO so its previous should be:
Card previous = ACE;//yes ACE
for (Card card : values()){
card.previous = previous;
previous = card;
}
}
Card(int value){
this.value = value;
}
public int getValue(){
return value;
}
public Card getPrevious(){
return previous; //<-- simple getter is enough since we took care
// of setting this value earlier in static
// initialization block
}
public String toString(){
return "The value of this card is: " + value;
}
}
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