数组与其他类 - 对象 - Java [英] Array withother classes - object - Java

问题描述

我有3个课程：课程， CourseEntry 和 Transcript 。在成绩单中，我有一个功能添加课程，如：

I have 3 classes: Course, CourseEntry and Transcript. In transcript, I have a function to add courses, like that:

public class Transcript {
    CourseEntry coursestaken[] = new CourseEntry[6];

    public void addCourse(Course course)
    {
        coursestaken[lastIndexOf(getCoursestaken())] = new CourseEntry(course);
    }
    (lastIndexOf gives me the empty array index - it's working on)

在 CourseEntry ：

public class CourseEntry {
    Course course;
    char grade = 'I';

    public CourseEntry(Course course)
    {
        this.course = course;
    }

在我的课程：

public  class Course {
    int courseNumber,credits;
    String courseName;

    public Course addNewCourse(int courseNumber, int credits, String courseName)
    {
        this.courseNumber = courseNumber;
        this.credits = credits;
        this.courseName = courseName;

        return this;
    }

在我的主页：

Transcript t = new Transcript();
Course course = new Course();

Course matematik = course.addNewCourse(1, 2, "Matematik");
t.addCourse(matematik);

Course turkce = course.addNewCourse(1, 4, "Türkçe");
t.addCourse(turkce);

但如果我循环coursestaken数组，它打印所有的最后插入的索引。

But if I loop coursestaken array, it prints the last inserted index for all.

我如何解决这个问题？

How can I solve that?

感谢

推荐答案

>在Java中，即指向对象的指针。所以当你这样做：

Objects are references in Java, that is, pointers to the objects. So when you do:

Object a = new Object();
Object b = a;

您不是复制整个对象 a 到 b ，但将 a 的引用复制到 b （内存地址）。因此 a 和 b 是对由 new

You're NOT copying the whole object a to b, but copying the reference to a to b (the memory address). So both a and b are references to the object created by new.

让我们按照您的代码，看看发生了什么：

Let's follow your code so you see what's happening:

Course course = new Course();
Course matematik = course.addNewCourse(1, 2, "Matematik");
    this.courseNumber = courseNumber;
    this.credits = credits;
    this.courseName = courseName;
    return this;

在此处修改 course 对象。 现在也与课程相同，因为它指向同一个对象。

Here you modified course object. matematik now is also the same as course because it points to same object.

Course turkce = course.addNewCourse(1, 4, "Türkçe");

这里可以再次修改 course 现在课程， turkce 和 matematik 都引用相同对象，您首先创建课程course =新课程（）; 。

Here you modify course again. Now course, turkce and matematik are all referencing the same object, which you created first with Course course = new Course();.

我认为最简单的方法修复这是你创建一个参数的构造函数：

I think most easy way to fix this is that you create a constructor with parameters:

public class Course {
...
     public Course(int courseNumber,int credits,String courseName) {
           this.courseNumber = courseNumber;
           this.credits = credits;
           this.courseName = courseName;
     }
}

，然后

  Course matematik = new Course(1, 2, "Matematik");
  t.addCourse(matematik);

  Course turkce = new Course(1, 4, "Türkçe");
  t.addCourse(turkce);

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