java - 无法弄清楚为什么某些变量不会初始化

Question

public static String produceAnswer(String y) {
    int space1Location = y.indexOf(" ");
    String value1 = y.substring(0, space1Location - 1);
    String value2 = y.substring(space1Location + 3);
    String operator = y.substring(space1Location + 1, space1Location + 2);
    int underLocation = value2.indexOf("_");
    int slashLocation = value2.indexOf("/");
    String wholeNum;
    String numerator;
    String denominator;
    if(underLocation != -1) {
        wholeNum = value2.substring(0, underLocation);
        numerator = value2.substring(underLocation + 1, slashLocation);
        denominator = value2.substring(slashLocation + 1);
    }
    else if(underLocation == -1 && slashLocation != -1) {
        numerator = value2.substring(0, slashLocation);
        denominator = value2.substring(slashLocation + 1);
        wholeNum = "0";
    }
    else if(underLocation == -1 && slashLocation == -1) {
        wholeNum = value2;
        numerator = "0";
        denominator = "1";
    }
    return "whole:" + wholeNum + " numerator:" + numerator + " denominator:" + denominator;
}

由于某种原因，我的代码中的 return 语句不起作用。它说变量尚未初始化，这对我来说没有意义，因为我肯定在 if 语句中对它们进行了初始化，对吗？这里有什么问题吗？

Answer 1

当您编写一个没有最终 else 的 if-else-if... 语句时，编译器不知道是否保证其中一个条件是true，这意味着它不确定您的局部变量是否会被初始化。

您应该将最后一个 else if 更改为 else。

if(underLocation != -1) {
    wholeNum = value2.substring(0, underLocation);
    numerator = value2.substring(underLocation + 1, slashLocation);
    denominator = value2.substring(slashLocation + 1);
} else if (underLocation == -1 && slashLocation != -1) {
    numerator = value2.substring(0, slashLocation);
    denominator = value2.substring(slashLocation + 1);
    wholeNum = "0";
} else {
    wholeNum = value2;
    numerator = "0";
    denominator = "1";
}

甚至:

if (underLocation != -1) {
    wholeNum = value2.substring(0, underLocation);
    numerator = value2.substring(underLocation + 1, slashLocation);
    denominator = value2.substring(slashLocation + 1);
} else if (slashLocation != -1) {
    numerator = value2.substring(0, slashLocation);
    denominator = value2.substring(slashLocation + 1);
    wholeNum = "0";
} else {
    wholeNum = value2;
    numerator = "0";
    denominator = "1";
}

因为如果第一个条件为false，我们已经知道underLocation在第二个条件下保证为-1，所以它是足以测试 slashLocation != -1。