java - 为什么我会收到 java.io.InvalidClassException？

Question

这个问题已经有答案了:

奥 git _a (5 个回答)

已关闭 9 年前。

我不知道为什么会发生这种情况。

    class Course implements Serializable
{


    private String campus;  // the campus on which the course is offered
    private String course;  // the course number, such as CSCI 111
    private String section; // the section number
    private String crn;     // the CRN for this section
    private int credits;    // the number od credits for the course
    private String time;    // the time the course is offered, such as 8:00 to 10:00 A.M.
    private String days;    // the Days the course is offered, suhc as MW


    // constructors
    Course() {
    }

    Course(String course, String section, String crn, int credits) {
        this.course = course;
        this.section = section;
        this.crn = crn;
        this.credits = credits;
    }   // end Course() initalizing

    // muatator methods

    public void setCampus(String cmp) {
        this.campus = cmp;
    }// end setCampus()

    public void setCourse(String crse) {
        this.course = crse;
    }// end setCourse()

    public void setSection(String sect) {
        this.section = sect;
    }   // end setSection()

    public void setCRN(String crn) {
        this.crn  = crn;
    }   // end setCRN()

    public void setCredits(int cr) {
        this.credits = cr;
    }   // end setCredits()

    public void setTime(String tm) {
        this.time = tm;
    }// end setTime()

    public void setDays(String days) {
        this.days = days;
    }// end setDays()


    // accessor methods

    public String getCampus() {
        return campus;
    }   // end getCampus()

    public String getCourse() {
        return course;
    }   // end Course()

    public String getSection() {
        return section;
    }   // end getSection()

    public String getCRN() {
        return crn;
    }   // end getCRN()

    public int getCredits() {
        return credits;
    }   // end getCredits()

    public String getTime() {
        return time;
    }   // end getTime()

    public String getDays() {
        return days;
    }   // end getDays()


    // method to compare by CRN using the String class compareTo()
    public int compareTo(Course other) {
        return this.crn.compareTo(other.getCRN());
    }   // end compareTO()

        // method to return properties as a string for csv file
//    public String toCSVString() {
//
//        return    credits
//                + campus + ","
//                + course + ","
//                + section + ","
//                + crn + " " + ","
//                + time + ","
//                + days;
//
//    }    // end toCSVString()

    // method to return properties as a string
    public String toString() {

        return    campus + " "
                + course + " "
                + section + " "
                + crn + " "
                + credits + " "
                + time + " "
                + days;

    }    // end toString()


}// end class Course

当我取消注释 toCSVString() 方法时，我得到 java.io.InvalidClassException

toCSVString 与 toString() 几乎相同，它不起作用对我来说没有任何意义。

这是完整的错误:

java.io.InvalidClassException: writecoursefile.Course; local class incompatible: stream classdesc serialVersionUID = -8471399827293588877, local class serialVersionUID = -3743045684326637976
    at java.io.ObjectStreamClass.initNonProxy(ObjectStreamClass.java:617)
    at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1622)
    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1517)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1771)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350)
    at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1706)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1344)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370)
    at writecoursefile.WriteCourseFile.readFromFile(WriteCourseFile.java:46)
    at writecoursefile.WriteCourseFile.main(WriteCourseFile.java:21)
Exception in thread "main" java.lang.NullPointerException
    at writecoursefile.WriteCourseFile.main(WriteCourseFile.java:24)
Java Result: 1

Answer 1

我没有在你的代码中看到你在哪里声明你的serialVersionUID - 但你需要声明它，并使其长。

例如:

私有(private)静态最终长serialVersionUID = 1L;

这里有一篇很好的文章解释了原因:

• http://www.mkyong.com/java-best-practices/understand-the-serialversionuid/