我為什么會收到錯誤消息：“線程“ main”中的異常“ java.lang.NullPointerException”

Question

當我運行程序時，出現以下錯誤：

 Exception in thread "main" java.lang.NullPointerException
    at study.calendar.HomeWorkDiary.<init>(HomeWorkDiary.java:51)
    at study.calendar.HomeworkTeftInterFace.main(HomeworkTeftInterFace.java:18)
Java Result: 1
BUILD SUCCESSFUL (total time: 1 second)

盡管我已經盡了最大的努力，但我仍然無法確定問題所在，我認為這與我聲明程序的方式有關。

可以通過識別並提供解決我的問題的方法來提供幫助，我們將不勝感激。

這是問題代碼：接口類：

public class HomeworkTeftInterFace {
    public static void main(String[] args) {
        HomeWorkDiary tefo = new HomeWorkDiary("test");
        String task1 = JOptionPane.showInputDialog("task");
        String subject1 = JOptionPane.showInputDialog("subject");
        double priorty1 = (Double.parseDouble(JOptionPane.showInputDialog("priorty")));
        int day1 = parseInt(JOptionPane.showInputDialog("due day"));
        int month1 = parseInt(JOptionPane.showInputDialog("month"));
        int year1 = parseInt(JOptionPane.showInputDialog("year"));
        tefo.addTask(task1, subject1, priorty1, day1, month1, year1);
    }
}

下課：

public HomeWorkDiary(String filename) {
//        System.out.println("test5");
        diary = new Homework[count + 50];
        count = 0;
//        System.out.println("test6");
        try {
            Scanner file = new Scanner(new File("HomeWork.txt"));
            file.useDelimiter("#");
            while (file.hasNextLine()) {
//                System.out.println("test3");
                String task = file.next();
                String subject = file.next();
//                System.out.println("test7");
                String priorty = file.next();
//                System.out.println("test9");
                String day = file.next();
                String month = file.next();
                String year = file.next();
//                System.out.println("test");
                diary[count].setTaks(task);
                diary[count].setSubject(subject);
                diary[count].setPrioity(Double.parseDouble(priorty));
                diary[count].setDay(parseInt(day));
                diary[count].setmonth(parseInt(month));
                diary[count].setyear(parseInt(year));
//                System.out.println("test 10");
                count++;
                file.nextLine();
            }
        } catch (FileNotFoundException f) {

        }
        System.out.println("test4");
    }

    public void addTask(String task1, String subject1, double priorty1, int day1, int month1, int year1) {
        diary[count].setTaks(task1);
        diary[count].setSubject(subject1);
        diary[count].setPrioity(priorty1);
        diary[count].setDay(day1);
        diary[count].setmonth(month1);
        diary[count].setyear(year1);
        count++;
    }

最后是數組類和相關方法：

public class Homework {

    private String subject;
    private String task;
    private double priorty;
    private int year;
    private int month;
    private int day;

    Homework(String task, String subject, double priorty, int year, int month, int day) {
        this.task = task;
        this.subject = subject;
        this.priorty = priorty;
        this.year = year;
        this.month = month;
        this.day = day;
    }

    public void setTaks(String task1) {
                System.out.println(task1);
        task = task1;
    }

    public void setSubject(String subject1) {
        System.out.println("test");
        subject = subject1;
    }

    public void setPrioity(double priorty1) {
        priorty = priorty1;
    }

    public void setDay(int day1) {
        day = day1;
    }

    public void setyear(int year1) {
        year = year1;
    }

    public void setmonth(int month1) {
        month = month1;
    }

這些代碼不是完整的類，而是我所使用的方法與我的問題有關。

Answer 1

您有一個數組diary其中帶有HomeWork 空引用 ，因此在將其用作diary[count] ，必須首先將其初始化為diary[count]=new HomeWork(); 在您的HomeWorkDiary構造函數中。