只有最后的对象被添加到ArrayList [英] Only the last Object is added to the ArrayList
问题描述
我创建的用户定义的数据类型,并从文件中读取数据。下面是codeS:
I created a user defined data type and read data from a file. Here are the codes:
学生班级:
package system.data;
public class Student {
private String firstName;
private String lastName;
private String regNumber;
private int coursework1Marks;
private int coursework2Marks;
private int finalExamMarks;
private double totalMarks;
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getRegNumber() {
return regNumber;
}
public void setRegNumber(String regNumber) {
this.regNumber = regNumber;
}
public int getCoursework1Marks() {
return coursework1Marks;
}
public void setCoursework1Marks(int coursework1Marks) {
this.coursework1Marks = coursework1Marks;
}
public int getCoursework2Marks() {
return coursework2Marks;
}
public void setCoursework2Marks(int coursework2Marks) {
this.coursework2Marks = coursework2Marks;
}
public int getFinalExamMarks() {
return finalExamMarks;
}
public void setFinalExamMarks(int finalExamMarks) {
this.finalExamMarks = finalExamMarks;
}
public double getTotalMarks() {
totalMarks = (coursework1Marks * 0.2) + (coursework2Marks * 0.2) + (finalExamMarks * 0.6);
return totalMarks;
}
}
和主要的编码:
public class MainInterface extends javax.swing.JFrame {
private File studentFile = new File(".\\StudentMarks.txt");
private PrintWriter printWriter = null;
private FileOutputStream fileOutputStream = null;
public ArrayList<Student> studentDetails = null;
private Scanner input = null;
private int counter = 0;
/**
* Creates new form MainInterface
*/
public MainInterface() {
initComponents();
setLocationRelativeTo(null);
studentDetails = new ArrayList<Student>();
ReadStudentDetails(studentDetails);
}
private void ReadStudentDetails(ArrayList<Student> studentDetails) {
ArrayList<String> strList = new ArrayList<>();
Student student = new Student();
try {
input = new Scanner(studentFile);
} catch (FileNotFoundException ex) {
Logger.getLogger(MainInterface.class.getName()).log(Level.SEVERE, null, ex);
}
while(input.hasNext()){
counter++;
String str = input.nextLine();
strList.add(str);
System.out.println(counter);
}
for (String item : strList) {
int x = 0;
String[] arr = item.split(":");
student.setFirstName(arr[0]);
student.setLastName(arr[1]);
student.setRegNumber(arr[2]);
student.setCoursework1Marks(Integer.parseInt(arr[3]));
student.setCoursework2Marks(Integer.parseInt(arr[4]));
student.setFinalExamMarks(Integer.parseInt(arr[5]));
studentDetails.add(student);
}
}
有没有语法错误给出。但是当我尝试ArrayList中打印的元素,
There no syntax errors given. But When I try to print the elements in the ArrayList as,
for(Student item: studentDetails){
System.out.println(item.getFirstName());
}
这给出了仅从文件的最后一条记录,(其中有3条记录)。这究竟是为什么?先谢谢了。
It gives out only the last record from the file, (which has 3 records). Why is this happening? Thanks in advance.
推荐答案
同样Student对象可重复使用,因为Java中传递,增加了学生的名单调用对象的引用。换句话说,原始的学生每次通过。解决的办法是为每次调用创建一个新学生。
The same student object is reused, because Java passes a reference to an object in the call that adds the student to the list. In other words, the original student is passed each time. The solution is to create a new Student for each call.
for (String item : strList) {
int x = 0;
String[] arr = item.split(":");
Student student = new Student();
student.setFirstName(arr[0]);
student.setLastName(arr[1]);
student.setRegNumber(arr[2]);
student.setCoursework1Marks(Integer.parseInt(arr[3]));
student.setCoursework2Marks(Integer.parseInt(arr[4]));
student.setFinalExamMarks(Integer.parseInt(arr[5]));
studentDetails.add(student);
}
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