"if" 语句中的局部变量错误 (Java)

Question

import java.util.Scanner;
import java.util.Random;
import static java.lang.System.out;

class TestingStuf {
    enum tooWhat {tooHigh, tooLow, justRight};

    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        Random myRandom = new Random();

        tooWhat guess;

        out.println("Pick a number between 1 and 10.");
        int userGuess = keyboard.nextInt(); 
        int randomNumber = myRandom.nextInt(10) + 1;

        if (userGuess < randomNumber) {
            guess = tooWhat.tooLow;
        }else if (userGuess > randomNumber) {
            guess = tooWhat.tooHigh;
        }else if (userGuess == randomNumber) {
            guess = tooWhat.justRight;
        }

        out.println("Your guess is:");

        if (guess == tooWhat.tooLow) {
            out.println("Too low.");

        }else if (guess == tooWhat.tooHigh) {
            out.println("Too high.");

        }else if (guess == tooWhat.justRight) {
            out.println("Correct!");

        }

            keyboard.close();
    }
}

在我的代码中，我在第二组 "if" 语句中有一个错误 "local variable guess may not have been initialized" 即使在之前的 "if" 语句中我给出了 "guess"变量取决于用户输入的值。我做错了什么？

Answer 1

如果您查看您的代码，似乎有一条通过 if...else if...else if 的路径，其中 guess 从未被初始化。这就是编译器警告您的内容，因为随后的代码预计 guess 肯定会有一个值。

虽然作为人类，我们知道您的三个条件是互斥的，但编译器并不像我们那么聪明。只需将您的最后一个设为 else 而不是 else if (...):

if (userGuess < randomNumber) {
    guess = tooWhat.tooLow;
}else if (userGuess > randomNumber) {
    guess = tooWhat.tooHigh;
}else { // *** No `if`
    guess = tooWhat.justRight;
}

Answer 2

将最后一个 if else 语句更改为 else 语句

 if (userGuess < randomNumber) {
        guess = tooWhat.tooLow;
    }else if (userGuess > randomNumber) {
        guess = tooWhat.tooHigh;
    }else 
        guess = tooWhat.justRight;

这样编译器就知道 guess 不可能保持未初始化状态。

Answer 3

编译器不确定是否应该根据仅通过 if..else if..else..if 阶梯为变量 guess 提供一个值。如果编译器要评估每个阶梯步骤的值，它就能够找出来，但这对编译器来说太过分了。按照代码，将 last else if 替换为 else 将解决您的问题。

"if" 语句中的局部变量错误 (Java)

Local variable error in "if" statement (Java)

java

variables

if-statement

local-variables