list<student> 的返回类型是什么？

Question

我想创建一个方法来填充student 的数据，方法签名为 public List<student> populateData(String filename).

我是 Java 新手。有人可以帮我解决这个问题吗？

我实现的代码是

public List<Student> populateData(String fileName) {
    // TODO Auto-generated method stub
    Scanner s = null;
    try {
        s = new Scanner(new File("F:\\Participant_Workspace\\Q3\\StudentDataManagementSystem\\StudentDetails.txt‌​"));
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    List<Student> list = new ArrayList<Student>();
    while (s.hasNext()){
        list.addAll(s.next());
    }
    s.close();
    return list;
}

但是添加arrayList<string> 和list.addAll(s.next()); 会出错。

Answer 1

假设你的文件是这样的。

abc 101

xyz 102

pqr 123

下面给出了一个简单的例子，进行修改并做你的事情。

public class PrintStudentsFromFile {

    public static void main(String[] args) {


     List<Student> students= new PrintStudentsFromFile().populateData("path to text file");


     for (Student student : students) {
            System.out.println(student);
        }
    }
    /**
     * Reads Files and returns a List of Students
     * @param filename
     * @return 
     */
    public List<Student> populateData(String filename){
    Scanner s = null;
    String nameAndRollNumber="";
        try {
            s = new Scanner(new File(filename));

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        List<Student> list = new ArrayList<Student>();
        while (s.hasNext()) {
        nameAndRollNumber = s.nextLine();
        String[] nameAndRollNumbers = nameAndRollNumber.split("\\s+");
        String name = nameAndRollNumbers[0];
        String roll = nameAndRollNumbers[1];
        list.add(new Student(name, roll));
        }
        s.close();
        return  list;
    }

}
/**
 * 
 * Student Object , with name and Roll Number Params
 */
class Student{

    String name;
    String rollNumber;

    public Student(String name, String rollNumber) {
        this.name = name;
        this.rollNumber = rollNumber;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getRollNumber() {
        return rollNumber;
    }

    public void setRollNumber(String rollNumber) {
        this.rollNumber = rollNumber;
    }

    @Override
    public String toString() {
        return "Name :"+name+"- Roll Number : "+rollNumber;
    }


}