Question

所有我一直在尝试将以下if语句转换为switch语句。

/**
 * Return appropriate comment for given score and par for hole.
 * You can assume that score is not less than 4 below par for hole.
 * For example, if score is 4 below par, return "condor!!!!",
 * if score is 3 below par, return "albatross!!!",
 * if score is 2 below par, return "eagle!!", etc.
 * See Assign 2 description for full list of comments.
 * @param score
 * @param parForHole
 * @return appropriate comment for given score and par for hole.
 */
public static String comment(int score, int parForHole) {   
    if ( score == parForHole-4)
        return "condor!!!!";
    if ( score == parForHole-3)
        return "albatross!!!";
    if ( score == parForHole-2)
        return "eagle!!";
    if ( score == parForHole-1)
        return "birdie!";
    if ( score == parForHole)
        return "par";
    if ( score == parForHole+1)
        return "bogey";
    if ( score == parForHole+2)
        return "double bogey";
    if ( score == parForHole+3)
        return "triple bogey";

return "Not valid"; // Replace by a suitable switch stmt.
}

这是我的尝试：

public static String comment(int score, int parForHole) {   

     String monthString;
        switch (score) {
            case parForHole-4:  monthString = "condor!!!!";
                     break;
            case parForHole-3:  monthString = "albatross!!!";
                     break;
            case parForHole-2:  monthString = "eagle!!";
                     break;
            case parForHole-1:  monthString = "birdie!";
                     break;
            case parForHole:  monthString = "par";
                     break;
            case parForHole+1:  monthString = "bogey";
                     break;
            case parForHole+2:  monthString = "double bogey";
                     break;
            case parForHole+3:  monthString = "triple bogey";
                     break;
            default: monthString = "Invalid";
                     break;
        }
        return monthString;

}

当我尝试运行它时，eclipse为每个案例条件提供了错误，即“case表达式必须是常量表达式”。我不知道如何克服这个问题。谁能帮我吗？感谢。

Answer 1

正如Eclipse试图告诉你的那样，这在Java中是不可能的。你只能在case语句中使用常量表达式，这在你的情况下并不适合。

无论如何，if-else和switch都不是很好。最好使用基于表格的解决方案，例如：

static String[] comments = {
    "condor!!!!",
    "albatross!!!",
    "eagle!!",
    "birdie!",
    "par",
    "bogey",
    "double bogey",
    "triple bogey"
};

public static String comment(int score, int parForHole) {
    int index = score - parForHole + 4;
    if (index < 0 || index >= comments.length) {
        return "Not valid";
    }
    return comments[index];
}

Answer 2

case语句中switch中的项必须编译时常量：

public static String comment(int score, int parForHole) {       
        switch (score - parForHole) {
            case -4:  
                     return "condor!!!!";
            case -3:  
                     return "albatross!!!";
            case -2:  
                     return "eagle!!";
            case -1:  
                     return "birdie!";
            case 0:  
                     return "par";
            case 1:  
                     return "bogey";
            case 2:  
                     return "double bogey";
            case 3:  
                     return "triple bogey";
            default: 
                     return "Invalid";
        }
}

Answer 3

请改为尝试：

public static String comment(int score, int parForHole) {   

 String monthString;
    switch (score - parForHole) {
        case -4:  monthString = "condor!!!!";
                 break;
        case -3:  monthString = "albatross!!!";
                 break;
        case -2:  monthString = "eagle!!";
                 break;
        case -1:  monthString = "birdie!";
                 break;
        case  0:  monthString = "par";
                 break;
        case +1:  monthString = "bogey";
                 break;
        case +2:  monthString = "double bogey";
                 break;
        case +3:  monthString = "triple bogey";
                 break;
        default: monthString = "Invalid";
                 break;
    }
    return monthString;

您的异常的原因是您正在尝试在case语句中进行计算 - 这是不允许的（因为异常状态，此处仅允许静态值）。上面的解决方案将计算结果引入switch语句，从而解决了您的问题。

尝试将if-else语句转换为switch语句但最终出现错误

3 个答案: