java - 我只为我的最终变量分配一个值，但仍然收到错误

Question

当我的实例字符串cardRank和cardSuit最终时，我遇到了错误，我认为我只在代码中为它们分配一次值。我已经在代码中评论了我正在谈论的内容。

import java.util.Arrays;

public class Card{

protected static final String[] SUITS = {"spades", "clubs", "hearts", "diamonds"};
protected static final String[] RANKS = {"1","2","3","4","5","6","7","8","9","10","J","Q","K"};

private String cardRank; // I want to make this final
private String cardSuit; // I want to make this final

public Card(){
    this(RANKS[(int) (Math.random() * RANKS.length)] , SUITS[(int) (Math.random() * SUITS.length)]);
}

public Card(String cardRank, String cardSuit){
    setRank(cardRank);
    setSuit(cardSuit);
}

private boolean isValidRank(String cardRank){
    cardRank = cardRank.toUpperCase();
    return Arrays.asList(RANKS).contains(cardRank);
}

private boolean isValidSuit(String cardSuit){
    cardSuit = cardSuit.toLowerCase();
    return Arrays.asList(SUITS).contains(cardSuit);
}

private void setRank(String cardRank){
    if(isValidRank(cardRank)) this.cardRank = cardRank;
    else this.cardRank = "Invalid Suit";
}

private void setSuit(String cardSuit){
    if(isValidSuit(cardSuit)) this.cardSuit = cardSuit;
    else this.cardSuit = "Invalid Suit";
}

public String getRank(){
    return cardRank;
}

public String getSuit(){
    return cardSuit;
}

public void printCard(){      
    System.out.println(getSuit() + " " + getRank());
}

}

Answer 1

您只能分配给构造函数主体内的final字段(或作为声明的一部分，或实例初始值设定项)。所以基本上，您应该放弃 setSuit 和 setRank 方法。

public Card(String cardRank, String cardSuit) {
    this.cardRank = isValidCardRank(cardRank) ? "Invalid rank";
    this.cardSuit = isValidCardSuit(cardSuit) ? "Invalid suit";
}

或者更好:

public Card(String cardRank, String cardSuit) {
    this.cardRank = validateRank(cardRank);
    this.cardSuit = validateSuit(cardSuit);
}

如果有效值无效，validate* 方法将抛出 IllegalArgumentException。

或者更好的是，创建 Suit 和 Rank 枚举，这样只有值是有效的，您只需要检查是否为空...