Question

所以我被困住了。我有一个fname lname sNum等学生名单。我正在尝试使用我的删除功能，但它不起作用。我无法弄清楚我的问题在哪里。

public void removeStudent(long sNumber) {
    //create student object
    Student student = new Student();
    //loop through the students 
    for (int i = 0; i < this.students.size(); i++) {
        //display students
        System.out.println(this.students.get(i));
        //condition if sNumber == sNumber 
        if(student.getsNumber() == sNumber){
            //remove the student from the list
            this.students.remove(student);
            System.out.println(this.students.get(i));
        }
        System.out.println("skipped the if statement");
    }
    /*for(Student student : this.students){
        if(student.getsNumber() == sNumber){
            this.students.remove(student);
        }
    }*/
}

这是我称之为方法的地方

case 3:
            // delete a student
            System.out.print("What is the Students sNumber: s");
            long sNum = input.nextLong();
            Student chkSNum = new Student();
            registry.getStudentBySNumber(sNum);
            chkSNum.setsNumber(sNum);
            if (registry.getStudentBySNumber(sNum) == chkSNum) {
                if (chkSNum.getsNumber() == sNum) {
                    registry.removeStudent(sNum);
                    System.out.println(chkSNum);
                }
            } else {
                System.out.println("Sorry no matches");
                // System.out.println(sNum);
                System.out.println(registry.getStudentBySNumber(sNum));
                System.out.println(chkSNum);
            }
            break;

我的添加学生方法效果很好。

    public void addStudent(Student student) {
    this.lastSNumber++;
    student.setsNumber(this.lastSNumber);
    this.students.add(student);
}

Answer 1

if(student.getsNumber() == sNumber)

将您的号码与新构建的空白Student对象进行比较。如果你想将它与你正在迭代的那些进行比较，你需要这样的东西：

if(this.students.get(i).getsNumber() == sNumber) {
    this.students.remove(i);
}

Answer 2

您实际上是删除了new studend()个对象。循环列表如下：

Student to_remove = null:
for(student s: this.students){
    if(s.getsNumber() == sNumber){
    to_remove = s;
    } 
    if(s!=null) break;
}
if(s!=null)this.students. remove(s);

这不会导致修改 - 异常

Answer 3

您应该使用迭代器在列表中删除。像

这样的东西

 Iterator<Student> it = this.students.iterator();
 while (it.hasNext()) {
 Student currentStudent = it.next();
 if(currentStudent.getsNumber() == sNumber)
  {
    it.remove();
   }
 }

Answer 4

所以我想出了什么是错的。我的逻辑是愚蠢的。

public void removeStudent(long sNumber) {
    //create student object
    //Student student = new Student();
    Student student = this.getStudentBySNumber(sNumber);
        //condition if sNumber == sNumber 
        if(student == this.getStudentBySNumber(sNumber)){
            System.out.println("removing the student from the list");
            this.students.remove(student);
            displayStudents();
        }
}

 case 3:
            // delete a student
            System.out.print("What is the Students sNumber: s");
            long sNumInput = input.nextLong();
            Student chkSNum2 = new Student();
            registry.getStudentBySNumber(sNumInput);
            chkSNum2.setsNumber(sNumInput);
            if (registry.getStudentBySNumber(sNumInput) != chkSNum2) {
                if (chkSNum2.getsNumber() == sNumInput) {
                    System.out.println("Student deleted...");
                    registry.removeStudent(sNumInput);
                }
            } else {
                System.out.println("Sorry no matches");
                System.out.println(registry.getStudentBySNumber(sNumInput));
                System.out.println(chkSNum2);
            }
            break;

Answer 5

removeStudent显然有些不对劲。首先，您要创建一个新的Student，然后使用该实例删除。

你应该做的是：

public void removeStudent(long sNumber) {
  for (Student s : this.students) {
    if (s.getNumber() == sNumber) { 
      this.students.remove(s);
    }
  }
}

您也可以使用代码中的for循环。这是一回事。请记住删除正确的实例。

希望有所帮助。

java使用list删除它与另一个不一样

5 个答案: