如何从 Java 中的数组列表返回特定对象(索引)? [英] How can I return a specific object (index) from an arraylist in Java?

问题描述

我创建了一个名为 Student 的类并为其分配了 3 个值(StudentNumber、Course、Mark)；然后我将一个创建的学生分配给一个名为 studentCourses 的数组列表.

I created a class called Student and assigned it 3 values (StudentNumber, Course, Mark); I then assigned a created student (s) to an arrayList called studentsCourses.

这样每个学生就占据了数组中的一个索引.但是我如何让学生们从 arrayList 中退出……如果这有意义的话?我已经存储了它们，但我不知道如何回忆这些信息以便我可以看到它.

This way each student takes up an index in the array. But how do I get the students back OUT of the arrayList... if that makes sense? I have them stored, but I don't know how to recall the information so that I can see it.

public static void main (String[]args){
ArrayList<Student> studentsCourses= new ArrayList<Student>();
String studentNumber="~";
String course="~";
int mark=0;

Student pat;

Student s=null;

do{
  s=new Student();
  System.out.println("Please Enter Your Student ID (type quit to Quit):\n");
  studentNumber=keybrd.next();
  s.setStudentNumber(studentNumber);
  System.out.println("Please Enter Your Course ID:\n");
  course=keybrd.next();
  s.setCourse(course);
  System.out.println("Please Enter Your Mark:\n");
  mark=keybrd.nextInt();
  s.setMark(mark);
  s.printStates();
  studentsCourses.add(s);
}while(!studentNumber.equals("quit"));

System.out.println(studentsCourses.size());   
System.out.println(studentsCourses);

所以如果我想为创建的学生 (pat) 分配索引 1 的状态，我该怎么做?

so if I wanted to assign the created student (pat) the state of index 1 how would I do that?

我的另一个问题(与这段代码一起)是我的哨兵.当我输入quit时它确实退出了.但它首先完成了do"的运行.这意味着我实际上最终得到了一个学生，他的编号是退出"课程是什么，而分数是什么.

My one other issue (going along with this piece of code) is my sentinel. it does indeed quit when I type quit. but it finishes running through the "do" first. meaning I actually end up with a student who's number is "quit" course is whatever and mark is whatever.

如何在输入quit"后立即强制它中断 do?

How do I force it to break the do as soon as "quit" is typed?

推荐答案

"但是我如何让学生从 arrayList 中退出...回忆起信息以便我可以看到它."

"But how do I get the students back OUT of the arrayList... if that makes sense? I have them stored, but I don't know how to recall the information so that I can see it."

从数组列表中获取数据:

To get the data from arraylist:

for (Student student : studentsCourses) {
        System.out.println(student.getStudentNumber());
        System.out.println(student.getCourse());
        System.out.println(student.getMarkr());
    }

或

for (int i = 0; i < studentsCourses.size(); i++) {
        Student student = studentsCourses.get(i);
        System.out.println(student.getStudentNumber());
        System.out.println(student.getCourse());
        System.out.println(student.getMarkr());
    }

要解决其他问题，您可以尝试:

to solve other issue, you can try:

      do{
          s=new Student();
          System.out.println("Please Enter Your Student ID (type quit to Quit):\n");
          studentNumber=keybrd.next();
          if(studentNumber.equals("quit"))
              break;
          s.setStudentNumber(studentNumber);
          System.out.println("Please Enter Your Course ID:\n");
          course=keybrd.next();
          s.setCourse(course);
          System.out.println("Please Enter Your Mark:\n");
          mark=keybrd.nextInt();
          s.setMark(mark);
          s.printStates();
          studentsCourses.add(s);
        }while(true);

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