代碼不會從課程中刪除學生[Java]

Question

與this post一樣的問題，但我認爲我越來越接近解決它。

簡而言之，我的代碼有兩門課程，我必須從每個課程中刪除一些學生，然後完全清除第二門課程。此代碼使用兩個類來完成。

這是我到目前爲止有：

/* 
Program description: 
Starting with listing 10.5 and 10.6 below, you are to modify the two source 
files to: 

Course.java: 


add method increaseArray(). 
Increase the array when students are added by 1, (hint utilize 
System.arraycopy method). Then add the student to the last location. I 
would suggest you set the size of the 「students」 array to a size initially 
of zero, so when the any student is added, your code to increase the 
array will be triggered. 

add method dropStudent(). 
Drop student would need to find the String match by iterating on the 
students array using the .equals String method. When a match is found, 
remove that entry by assigning the next student into the match location, 
and do for all the remaining students (effectively shift remaining 
students by one). Also you would have also decrement the 
numberOfStudents count. 

add method clear(). 
Iterating on the students array assign all to null and set the 
numberOfStudents count to 0. 
TestCourse.java: 
You need to test your new methods; this is done by modifying listing 10.5 to 
meet the requirements of assignment which are: 

Create a two courses 
Add six students to the first, three students to the second 
Remove the first two student from course one 
Remove the second student from course two 
Display students in both classes 
Clear the second course 
Display students in both classes 


Add a static method to TestCourse that handles printing the students in a 
class. This method receives the reference of the course and the course 
number. This way, you just call the method to print out the students. 
*/ 

public class Course { 
private String courseName; 
private String[] students = new String[100]; 
private int numberOfStudents; 

public Course(String courseName) { 
    this.courseName = courseName; 
} 

public void addStudent(String student) { 
    students[numberOfStudents] = student; 
    numberOfStudents++; 
} 

public String[] getStudents() { 
    return students; 
} 

public int getNumberOfStudents() { 
    return numberOfStudents; 
} 

public String getCourseName() { 
    return courseName; 
} 

public void dropStudent(String student) { 

    int IndexOfStudentToDrop = -1; 

    for (int i = 0; i < numberOfStudents; i++) { 
     if (students[i].equalsIgnoreCase(student)) { 
      IndexOfStudentToDrop = i; 
      if (IndexOfStudentToDrop != -1) { 
       for (i = IndexOfStudentToDrop; i < numberOfStudents; i++) 
        students[i] = students[i+1]; 
      } // end if found 
      // decrement number of students by 1 
      numberOfStudents--; 
     } 
    } 

} 

public void clear() { 

    for (int i = 0; i < numberOfStudents; i ++){ 
     students [i] = null; 
    } 
    numberOfStudents = 0; 

} 

public void increaseArray() { 
    if (numberOfStudents >= students.length) { 
     String[] temp = new String[students.length * 2]; 
     System.arraycopy(students, 0, temp, 0, students.length); 
     students = temp; 
    } 



} // end of increaseArray() 

public String toString() 
{ 
    String output = ""; 
    output += getCourseName()+ (getNumberOfStudents() + "students"); 
     for (int i = 0; i < getNumberOfStudents(); i++) { 
       output += "\n("+ (i + 1)+")"+ students [i]; 
      } 
    return output; 

} 
} 

和

public class TestCourse { 
public static void main(String[] args) { 

    // create two courses 
    Course course1 = new Course("Data Structures"); 
    Course course2 = new Course("Database Systems"); 

    // introduce the program 
    System.out.println("Creating Two Courses"); 
    System.out.println("Adding 6 students to course 1"); 
    System.out.println("Adding 3 students to course 2"); 


    // add six students to course1 
    course1.addStudent("\n1: Tom Servo"); 
    course1.addStudent("\n2: Joel Robinson"); 
    course1.addStudent("\n3: Mike Nelson"); 
    course1.addStudent("\n4: Pearl Forrester"); 
    course1.addStudent("\n5: TV's Frank"); 
    course1.addStudent("\n6: Zap Rowsdower"); 
    System.out.println(); 
    System.out.println(); 




    // add three students to course2 
    course2.addStudent("\n1: Tom Servo"); 
    course2.addStudent("\n2: Crow T. Robot"); 
    course2.addStudent("\n3: Zap Rowsdower"); 
    System.out.println(); 
    System.out.println(); 



    // output to the console 
    System.out.println ("Number of students in Course 1: " + course1.getNumberOfStudents() + " Students are: "); 
    String [] students = course1.getStudents(); 

    for (int i = 0; i < course1.getNumberOfStudents(); i++) 
     System.out.print(students[i]); 


    System.out.println(); 
    System.out.print("Number of students in Course 2: " + course2.getNumberOfStudents() + " Students are: "); 
    String [] students1 = course2.getStudents(); 

    for (int i = 0; i < course2.getNumberOfStudents(); i++) 
     System.out.print(students1[i]); 

    // output to the console how many students will be dropped from each class 
    System.out.println("dropping 2 students from course 1"); 
    System.out.println("dropping 1 student from course 2"); 


    // drop some students. 
      course1.dropStudent("Tom Servo"); 
      course1.dropStudent("Joel Robinson"); 
      System.out.println ("\nNumber of students in Course 1: " + course1.getNumberOfStudents() + " Students are: "); 

      course2.dropStudent("Crow T. Robot"); 
      System.out.println("\nNumber of students in Course 2: " + course2.getNumberOfStudents() + " Students are: "); 

    // clear course2, but keep course1 as it currently stands 
      System.out.println("\nclearing course 2 course 2"); 
      course2.clear(); 

      System.out.println("\nNumber of students in Course 1: " + course1.getNumberOfStudents() + " Students are: "); 
      System.out.println("\nNumber of students in Course 2: " + course2.getNumberOfStudents() + " Students are: "); 
    } 

} 

這就是輸出應該是這樣的：

Creating Two Courses 
Adding 6 students to course 1 
Adding 3 students to course 2 

Number of students in Course 1: 6 Students are: 
1: Tom Servo 
2: Joel Robinson 
3: Mike Nelson 
4: Pearl Forrester 
5: TV's Frank 
6: Zap Rowsdower 

Number of students in Course 2: 3 Students are: 
1: Tom Servo 
2: Crow T. Robot 
3: Zap Rowsdower 

dropping 2 students from course 1 
dropping 1 student from course 2 

Number of students in Course 1: 4 Students are: 
1: Mike Nelson 
2: Pearl Forrester 
3: TV's Frank 
4: Zap Rowsdower 

Number of students in Course 2: 2 Students are: 
1: Tom Servo 
2: Zap Rowsdower 

clearing course 2 course 2 

Number of students in Course 1: 4 Students are: 
1: Mike Nelson 
2: Pearl Forrester 
3: TV's Frank 
4: Zap Rowsdower 

Number of students in Course 2: 0 Students are: 

但是，這是什麼情況相反：

Creating Two Courses 
Adding 6 students to course 1 
Adding 3 students to course 2 




Number of students in Course 1: 6 Students are: 

1: Tom Servo 
2: Joel Robinson 
3: Mike Nelson 
4: Pearl Forrester 
5: TV's Frank 
6: Zap Rowsdower 
Number of students in Course 2: 3 Students are: 
1: Tom Servo 
2: Crow T. Robot 
3: Zap Rowsdowerdropping 2 students from course 1 
dropping 1 student from course 2 

Number of students in Course 1: 6 Students are: 

Number of students in Course 2: 3 Students are: 

clearing course 2 course 2 

Number of students in Course 1: 6 Students are: 

Number of students in Course 2: 0 Students are: 

正如您所看到的，我的代碼不會在學生需要時放棄（儘管清理似乎不成問題）。我知道我的格式已經搞亂了，但這不是我主要關心的問題，我可以自己解決。除了格式化之外，丟失的學生是我唯一的問題，如果我能夠得到幫助，我可以從這裏拿走。

Answer 1

這不工作的原因是：你把琴絃一樣1: Tom Servo與數量，並試圖像course1.dropStudent("Tom Servo");

刪除它們。如果你要麼刪除1:添加Student時，或者你會嘗試刪除它們爲：

course1.dropStudent("1: Tom Servo"); 

我確定它會工作。