Java Beans測試一個類

Question

給了我一個類DrivingTestM.java來測試我編寫的2個類。 這是我寫的課程。 當我運行DrivingTestM.java時，出現以下錯誤：

System.out.println( question.getDescription() );

我不確定錯誤可能是什么。 任何人都可以嘗試闡明此錯誤嗎？ 謝謝！

Question.java：

public class Question {
String description;
String answerA;
String answerB;
String answerC;
int correctAnswer;
int answer;
Boolean answerCorrect;

public Question(){

}
public Question(String description, String answerA, String answerB, String answerC, int correctAnswer, int answer){
    this.description = description;
    this.answerA = answerA;
    this.answerB = answerB;
    this.answerC = answerC;
    this.correctAnswer = correctAnswer;
    this.answer = answer;

}
public Question(String description, String answerA, String answerB, String answerC, int correctAnswer){
    this.description = description;
    this.answerA = answerA;
    this.answerB = answerB;
    this.answerC = answerC;
    this.correctAnswer = correctAnswer;
}

public Boolean isAnswerCorrect() {
    return answerCorrect;
}
public String getDescription() {
    return description;
}
public void setDescription(String description) {
    this.description = description;
}
public String getAnswerA() {
    return answerA;
}
public void setAnswerA(String answerA) {
    this.answerA = answerA;
}
public String getAnswerB() {
    return answerB;
}
public void setAnswerB(String answerB) {
    this.answerB = answerB;
}
public String getAnswerC() {
    return answerC;
}
public void setAnswerC(String answerC) {
    this.answerC = answerC;
}
public int getCorrectAnswer() {
    return correctAnswer;
}
public void setCorrectAnswer(int correctAnswer) {
    this.correctAnswer = correctAnswer;
}
public int getAnswer() {
    return answer;
}
public void setAnswer(int answer) {
    this.answer = answer;
}
}

DrivingTest.java：

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class DrivingTest {
int currentQuestionIndex = 0;
Question currentQuestion;
Boolean lastQuestion;
int score;
List<Question> q = new ArrayList<Question>();
Question quest = new Question();

public DrivingTest() throws FileNotFoundException{
    File f = new File("DrivingTest.txt");
    //int n = 1;
    Scanner sc = new Scanner(f);

    while(sc.hasNextLine()){
        String desc = sc.nextLine();
        String A =  sc.nextLine();
        String B =  sc.nextLine();
        String C =  sc.nextLine();
        String h =  sc.nextLine();
        int a = Integer.parseInt(h);
        String blank = sc.nextLine();
        q.add(new Question(desc, A,B,C,a) );
        }
        sc.close();
    }

public void setCurrentQuestionIndex(int currentQuestionIndex) {
    this.currentQuestionIndex = currentQuestionIndex;
}
public int getCurrentQuestionIndex() {
    return currentQuestionIndex;
}

public Boolean isLastQuestion() {
    if(currentQuestionIndex == q.size() - 1){
        return true;
    }
    else{
        return false;
    }
}

public Question getCurrentQuestion() {
    return currentQuestion;
}

public void setCurrentQuestion(Question currentQuestion) {
    this.currentQuestion = currentQuestion;
}

public int getScore() {
    return score;
}
}

DrivingTestM.java（測試文件）：

import java.io.FileNotFoundException;

public class DrivingTestMain {

public static void main( String args[] ) throws FileNotFoundException
{
    DrivingTest drivingTest = new DrivingTest();

    while( true )
    {
        // display the current question
        Question question = drivingTest.getCurrentQuestion();
        System.out.println( question.getDescription() );
        System.out.println( "\t" + question.getAnswerA() );
        System.out.println( "\t" + question.getAnswerB() );
        System.out.println( "\t" + question.getAnswerC() + "\n" );

        // set the answer to the current question to 1
        drivingTest.getCurrentQuestion().setAnswer( 1 );

        // if this is the last question, we are done.
        if( drivingTest.isLastQuestion() ) break;

        // it is not the last question, so increment CurrentQuestionIndex
        int currentQuestionIndex = drivingTest.getCurrentQuestionIndex();
        drivingTest.setCurrentQuestionIndex( currentQuestionIndex + 1 );
    }

    // display the test score
    System.out.println( "Your test score is: " + drivingTest.getScore() );
}
}

Answer 1

您在嘗試使用當前問題之前未在任何地方設置當前問題。

您需要類似以下方法：

public void startTest()
{
    currentQuestion = q.get(0);
}

接着：

   DrivingTest drivingTest = new DrivingTest();
   drivingTest.startTest();

   while( true )
   {
   //....

還要確保您有疑問要解決，否則您也會遇到其他錯誤。

如果您使用的是eclipse，請嘗試逐步調試代碼...

您可能還想尋找一種更好的方法來終止該循環，目前它會在測試結束時失敗...

編輯：好的循環不會中斷，但它的確很雜亂...

編輯DrivingTest構造函數：

public DrivingTest() throws FileNotFoundException{
File f = new File("DrivingTest.txt");
//int n = 1;
Scanner sc = new Scanner(f);

while(sc.hasNextLine()){
    String desc = sc.nextLine();
    String A =  sc.nextLine();
    String B =  sc.nextLine();
    String C =  sc.nextLine();
    String h =  sc.nextLine();
    int a = Integer.parseInt(h);
    String blank = sc.nextLine();
    q.add(new Question(desc, A,B,C,a) );
    }
    sc.close();

    //ensure it's 0.
    currentQuestionIndex = 0;
    //sets up your first question object.
    setCurrentQuestion( q.get(currentQuestionIndex) );
}

Answer 2

您將得到java.lang.NullPointerException，因為您將Question對象存儲在Q列表中，但沒有從中讀取對象。 在主類中嘗試類似的方法，而不是：

Question question = drivingTest.getCurrentQuestion();

采用

List<Question> qList = drivingTest.getQ();
Question question = qList.get(i);

還可以在DrivingTest類中添加Q getter。

如果您不想修改主類，而只需要在getCurrentQuestion（）方法中進行更改：

int i = 0;
public Question getCurrentQuestion() {
    if (i<q.size()-1) 
         return q.get(i++);
    else return q.get(i);
}

。