[英]Objects are being overwritten each time i iterate over the loop
在每次迭代中,我添加一个新的Student对象,它将覆盖之前的对象,并在整个列表中包含相同的对象。 我尝试使用链接列表和数组列表,但仍然遇到相同的问题。 如果有人能很好地指导我朝正确的方向发展,我将不胜感激。 谢谢。
public static void main(String[] args) {
// Scanner and LinkedList
Scanner keyboard = new Scanner(System.in);
LinkedList<Student> studentList = new LinkedList<Student>();
ArrayList<Student> stdList = new ArrayList<Student>();
int choice;
boolean flag = true;
do {
Student.showMenu();
choice = keyboard.nextInt();
switch (choice) {
case 1: {
System.out.println("What is the students last name?");
String last = keyboard.next();
System.out.println("What is the students first name?");
String first = keyboard.next();
System.out.println("What is the students course code?");
int courseCode = keyboard.nextInt();
System.out.println("What is the students course grade?");
String grade = keyboard.next();
Student st = new Student(last, first, courseCode, grade);
studentList.add(st);
stdList.add(st);
break;
}
case 2: {
System.out
.println("Please enter the students last name you wish to delete.");
String last = keyboard.next();
int index = Student.indexOf(studentList, last);
if (index != -1)
studentList.remove(index);
else
System.out.println("Student does not exist.");
break;
}
case 3: {
System.out
.println("Please enter the students last name you wish to search.");
String last = keyboard.next();
int index = Student.indexOf(studentList, last);
if (index != -1)
studentList.get(index).toString();
else
System.out.println("Student does not exist.");
break;
}
case 4: {
System.out.println("");
break;
}
case 5:
System.out.println("");
break;
case 6:
Student.displayList(studentList);
break;
case 7:
flag = false;
break;
}
} while (flag);
}
public class Student {
private static String last;
private static String first;
private static int courseCode;
private static String grade;
public Student(String last, String first, int courseCode, String grade) {
this.last = last;
this.first = first;
this.courseCode = courseCode;
this.grade = grade;
}
public String getLast() {
return last;
}
public void setLast(String last) {
this.last = last;
}
public String getFirst() {
return first;
}
public void setFirst(String first) {
this.first = first;
}
public int getCourseCode() {
return courseCode;
}
public void setCourseCode(int courseCode) {
this.courseCode = courseCode;
}
public String getGrade() {
return grade;
}
public void setGrade(String grade) {
this.grade = grade;
}
public static void showMenu() {
System.out.println("Welcome to the database menu!\n");
System.out.println("Press 1 to insert a new record");
System.out.println("Press 2 to delete a record");
System.out.println("Press 3 to search the database (by last name)");
System.out.println("Press 4 to print a range in the database");
System.out.println("Press 5 to find the class average for a course");
System.out.println("Press 6 to print the list");
System.out.println("Press 7 to quit");
}
public String toString() {
String str = " Last name: " + last + " First name: " + first
+ " Course code: " + courseCode + " Course grade: " + grade;
return str;
}
static int indexOf(LinkedList<Student> list, String last) {
int i = 0;
for (Student std : list) {
if (std.getLast().equals(last))
return i;
i++;
}
return -1;
}
static void displayList(LinkedList<Student> list) {
for (int i = 0; i < list.size(); i++) {
System.out.println(list.get(i).toString() + " ");
}
}
static void displayList(ArrayList<Student> stdList) {
for (int i = 0; i < stdList.size(); i++) {
System.out.println(stdList.get(i).toString() + " ");
}
}
}
那是一个相当奇怪的问题。 我最好的建议是改变
Student st = new Student(last, first, courseCode, grade);
studentList.add(st);
stdList.add(st);
至
studentList.add(new Student(last, first, courseCode, grade));
stdList.add(new Student(last, first, courseCode, grade));
问题是你上市代码不添加方法,请检查您的迭代的代码,如果你使用的是常规的迭代for
是
for(int i = 0; i
那么您必须提交经典的初学者错误,该错误是每次迭代都获取第一项,而不是使用分配的变量,例如
List.get(0)
而不是List.get(i)
我建议您针对此类实例将增强功能也称为foreach
问题是您已将class Student
私有成员定义为static
。 任何理由将它们标记为static
。 请删除静态代码,您的代码应该可以正常工作。
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