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我有点迷茫...我正在学习 Java 并且必须编写一个小型轮询命令行应用程序。
我们应该先用德语编写程序(为了我们所有人之间的一致性)，所以我会尝试翻译它，以便您更容易阅读。 我的问题是，它抛出异常(在编译时)如下:
Exception in thread "main" java.lang.NullPointerException
at communication.Poll.addQuestionItem(Poll.java:18)
at main.PollTool.main(PollTool.java:8)
我初始化我的数组“questionItems”是不是错了？我不应该那样做吗？这里出了什么问题？我忘了什么吗？ :(
main.PollTool:
package main;
import communication.Poll;
public class PollTool {
public static void main(String[] args) {
Poll poll = new Poll ("Best Smartphone:",3);
poll.addQuestionItem("iPhone"); //<--line 8
poll.addQuestionItem("Android");
poll.addQuestionItem("Windows Phone");
poll.askQuestions("This poll determines the polularity of different Smartphones.");
}
}
交流。投票:
package communication;
import java.util.Scanner;
import calculations.QuestionItem;
public class Poll {
private String questionTitle;
private QuestionItem[] questionItems;
private int count;
private Scanner in = new Scanner(System.in);
public Poll(String s,int arraySize){
questionTitle = s;
questionItems = new QuestionItem[arraySize]; //<--problem here?
}
public void addQuestionItem(String s){
if(count<questionItems.length){
questionItems[count++].setItemText(s); // <--exception here
}
}
public void askQuestions(String topic){
System.out.println(topic);
System.out.println(questionTitle);
for(int i=0; i<questionItems.length; i++){
System.out.println("- - - "+ questionItems[i].getItemText() +" - - -");
System.out.print("Your numerical answer: ");
questionItems[i].vote(in.nextInt());
}
}
void evaluation(){
//not ready :)
}
}
计算.问题项:
package calculation;
public class QuestionItem {
int count;
int overall;
String text;
public void vote (int pointValue){
overall += pointValue;
count++;
}
public double getDurchschnitt(){
return (double) overall/count;
}
public void setItemText(String s){
text = s;
}
public String getItemText(){
return text;
}
}