我是否过度简化了回报？

Question

基本上，我正在为一门大学课程做旧的驾驶员考试计划，并且我已经起草了整个班级。当我尝试编译它时，如果在命令提示符下工作，我会收到错误：

缺少返回语句

在 Eclipse 中：

此方法必须返回与我的方法有关的 int` 类型的结果，因为我错过了问题。

现在我想我在尝试编译之前就已经知道问题所在了 - 我的方法是 int 类型，并且因为我的答案是“array is char”，所以当我尝试返回 'index + 1' 或 'index++ ) 它返回实际元素，一个字符（即答案 a、b、c、d）。我想要做的是返回下标数字+1（以一个错误删除），所以当我编写程序时，我可以系统输出打印'你错过了问题1、3、5等'。

我意识到这段代码中可能还有一百万个错误，但现在我只是希望有人能帮助我解决这个问题。意识到这可能既简单又愚蠢，但是已经阅读论坛和我的教科书几个小时了，却无法弄清楚。也许我只是通过使用下标 + 1 作为显示遗漏问题编号的一种方式来简化太多。

public class DriverExam {

private char[] rightAnswers = { 'b', 'd', 'a', 'a', 'c', 'a', 'b', 'a',   
'c', 'd', 'b', 'c', 'd', 'a', 'd', 'c', 'c', 'b', 'd', 'a' }; //Answers 
to test.
char[] Answers; //Student answer input.
int[] missed = {}; //Array for missed questions.
int correct = 0; //Create and initialise to 0.
int qMissed = 0; //Create and initialise to 0.

/** 
Constructor that accepts array of answers and copies to the answers array 
field.
@parem ans The array of student driver answers */


public DriverExam(char[] ans)
{
Answers = ans;
}

/**
An int array containing the question numbers of those questions that the 
student missed.
*/

public int questionsMissed() 

{
for (int index = 0; index < 20; index++) //Ask program to step through 
each element in array Answers.
    {
    if (Answers[index] == 0) //I'm assuming here that a question not 
    answered = 0, not null as it would for string.
        return index + 1; //I want to return the subscript assigned to 
    any questions that = 0 ie haven't been answered, plus 1 to avoid out 
    by one error.
    }
    }

public int qMissed() 
{
for (int index = 0; index < 20; index++) //Ask program to step through    
each element in array Answers.
    {
    if (Answers[index] == 0) //Asking it to repeat process above.
        return index++; //I want to ask it to take the subscript and add 
1 to the existing subscript for all additional missed questions.
        }
}


/**
A method that returns the total number of correctly answered questions.
@return Returns the number of correctly answered questions.
*/

public int totalCorrect()
{
for (int index = 0; index < Answers.length; index++)
{
if (Answers[index] == rightAnswers[index]) 
correct++;
}
return correct;
}


/**
A method that returns the total number of incorrectly answered questions.
@return Returns the number of incorrect answers.
*/

public int totalIncorrect()
{
    int incorrect = (rightAnswers.length - (totalCorrect() + qMissed));
    return incorrect;
}

/**
A method that returns true if the student passed the exam, or false if    
the student failed.
*/


public boolean passed()
{
    if(totalCorrect() >= 10); return true;
}

}

Answer 1

您需要添加一行来为 else 部分返回一个 int。当您在函数中有non-void 返回类型时，您需要显式地为所有代码分支（if-else）返回一个值。

public int questionsMissed() 

{
for (int index = 0; index < 20; index++) 
    {
    if (Answers[index] == 0) 
        return index + 1; 
    }

在这里为前return -1返回一个int

}

Answer 2

如果您的方法已声明返回int，它必须在任何情况下返回int，如果您想循环所有项目并检查数组是否包含'0'。如果全部失败return -1或@ 987654324@

public int questionsMissed() {
    for (int index = 0; index < 20; index++) {
        if (Answers[index] == 0) {
            return index + 1;
        }
    }
  return -1;//If nothing works
}

注意：变量名应以小写开头。回答而不是回答

Answer 3

警告是因为在 questionsMissed 和 qMissed 两个函数中，返回类型都应该是 int。在检查if 条件后，您将在循环内返回，这是绝对正确的，但是当if 语句永远不会计算为真时会发生什么，您的函数将永远不会返回任何内容，这就是警告的原因。为避免这种情况，您应该在for 循环之后添加一个返回语句。

Answer 4

几个建议：

1) 您将正确答案保存在数组中的方法很好。将实际答案传递给构造函数的想法也是如此。好！

2) 每次您想知道#/正确答案或#/不正确答案时，与其遍历两个数组，不如只遍历数组ONCE，然后保存供您将来参考所需的一切。在你的情况下，我在构造函数中做了这个。

3) 迟早你会遇到"Java Beans" 和"getter and setter" 方法。严格来说，您的“DriverExam”不是 Java Bean（它没有零参数构造函数），但标准的“getter”命名约定很有用。我已将您的字段标记为“私有”并将您的访问方法更改为“getter”命名约定：getTotalCorrect() 等。

4) 我还添加了一个检查，如果学生碰巧回答的问题少于整个测试。

这里是修改后的代码：

public class DriverExam {

    //Answers to test
    private char[] rightAnswers = { 
        'b', 'd', 'a', 'a', 'c', 'a', 'b', 'a',   
        'c', 'd', 'b', 'c', 'd', 'a', 'd', 'c', 'c', 'b', 'd', 'a' 
    }; 

    private boolean[] results;
    private int totalCorrect = 0; //Create and initialise to 0.
    private int totalMissed = 0; //Create and initialise to 0.

    /** 
    Constructor that accepts array of answers, grades the text, and computes #/correct and #/missed
    */
    public DriverExam(char[] ans)   {
        // Allocate array to hold results
        results = new boolean[rightAnswers.length];

        // Grade the test
        for (int i=0; i < rightAnswers.length; i++) {
            // ... Q: Did student complete this part of the test?
            if (i > ans.length-1) {
                results[i] = false;  //  Mark "incorrect"
                totalMissed++;
            }
            else if (ans[i] != rightAnswers[i]) {
                results[i] = false; // Mark "incorrect"
                totalMissed++;
            }
            else {
                results[i] = true;  // Mark "correct"
                totalCorrect++;

            }
        }
    }

    /**
    An boolean array containing which questions were answered correctly, and which weren't
    */
    public boolean[] getResults() {
        return results;
    }

    /**
    A method that returns the total number of correctly answered questions.
    */
    public int getTotalCorrect()    {
        return totalCorrect;
    }

    /**
    A method that returns the total number of questions missed.
    */
    public int getTotalMissed() {
        return totalMissed;
    }

    /**
    A method that returns true if the student passed the exam, or false if    
    the student failed.
    */
    public boolean isPassed()   {
        return (totalCorrect >= 10);
    }


    /**
     * Test driver
     */
    public static void main (String[] args) {
        char[] myAnswers = {
            'b', 'x', 'x', 'a', 'c', 'a', 'b', 'a',   
            'c', 'd', 'b', 'c', 'd', 'a', 'd', 'c', 'c', 'b', 'd', 'a' 
        }; 

        DriverExam myExam = new DriverExam (myAnswers);
        System.out.println ("#/correct=" + myExam.getTotalCorrect() + ", #/missed=" + myExam.getTotalMissed() + ", passed=" + myExam.isPassed());
        System.out.println("Questions missed: ");
        boolean[] myResults = myExam.getResults();
        for (int i=0; i < myResults.length; i++) {
            if (myResults[i] == false)
                System.out.println ("  " + i);
        }

    }
}

这是示例输出：

#/correct=18, #/missed=2, passed=true
Questions missed: 
  1
  2

Answer 5

我认为返回 index++ 或 index + 1 应该没问题，但似乎并非所有代码路径都返回 int。例如，在 questionsMissed() 中，您有一个 if 语句来检查 0 并在这种情况下返回一个 int，但如果检查返回 false，则不会返回任何 int。你可以把它改成这样：

public int questionsMissed() 
{
    for (int index = 0; index < 20; index++)
    {
        if (Answers[index] == 0)
        {
            return index + 1;
        }
    }
    return 0;
}