Question

我正在尝试在对象数组列表上执行二进制搜索。用户必须输入管理员号码才能执行搜索。这是我的代码：

从.text文件中读取文件的文件控制器类

public class FileController extends StudentApp{
private String fileName;

public FileController() {
    String fileName = "student.txt";
}

public FileController(String fileName) {
    this.fileName = fileName;
}

public ArrayList<String> readLine() {
    ArrayList<String> studentList = new ArrayList<String>();
    try {
        FileReader fr = new FileReader(fileName);
        Scanner sc = new Scanner(fr);
        while (sc.hasNextLine()) {
            studentList.add(sc.nextLine());
        }
        fr.close();
    } catch (FileNotFoundException exception) {
        System.out.println("File " + fileName + " was not found");
    } catch (IOException exception) {
        System.out.println(exception);
    }
    return studentList;
}

学生班与所有的二传手和getter和compareTo方法

public Student(String adminNo, String name, GregorianCalendar birthDate) {
    this.adminNo = adminNo;
    this.name = name;
    this.birthDate = birthDate;
}

public Student(String record) {
    Scanner sc = new Scanner(record);
    sc.useDelimiter(";");
    adminNo = sc.next();
    name = sc.next();
    birthDate = MyCalendar.convertDate(sc.next());
    test1 = sc.nextInt();
    test2 = sc.nextInt();
    test3 = sc.nextInt();
}
public String toString(){
    return (adminNo + " " + name + " " + MyCalendar.formatDate(this.birthDate));
}

public static ArrayList<Student> readStudent(String file) {
    FileController fc = new FileController(file);
    ArrayList<Student> recs = new ArrayList<Student>();
    ArrayList<String> recsReturn = new ArrayList<String>();

    recsReturn = fc.readLine();

    for (int index = 0; index < recsReturn.size(); index++) {
        String input = recsReturn.get(index);
        recs.add(new Student(input));
    }

    return recs;
}


public int compareTo(Student s) {
    return Compare(this, s);
}

public int Compare(Student s1, Student s2){
    if(s1.getAdminNo().equals(s2.getAdminNo())) {
      return 0;
    }else{
      return 1;
    }
}

可执行的主要方法在于StudentSearch Class

public static void main(String [] args){
    Scanner sc = new Scanner(System.in);
    ArrayList <Student> studentList = new ArrayList <Student> ();
    studentList = Student.readStudent("student.txt");
    Collections.sort(studentList);

    System.out.println("Enter student admin number: ");
    String searchAdminNo = sc.next();

    int pos = Collections.binarySearch(studentList, new   Student(searchAdminNo));
    System.out.println(pos);
}

我想使用用户输入管理员号码执行搜索。但是，这是错误消息：

Exception in thread "main" java.util.NoSuchElementException
at java.util.Scanner.throwFor(Unknown Source)
at java.util.Scanner.next(Unknown Source)
at StudentGradeApps.Student.<init>(Student.java:22)
at StudentGradeApps.StudentSearch.main(StudentSearch.java:14)

我认为问题在于compareTo方法和我的二进制搜索。因为当我删除它们时，我的程序可以使数组列表正常。只有当我尝试在对象列表上执行搜索时才会出现此错误。任何帮助将不胜感激。

提前致谢。

Answer 1

如错误消息所示，异常发生在Student构造函数 -

中

public Student(String record) {
    Scanner sc = new Scanner(record);
    sc.useDelimiter(";");
    adminNo = sc.next();
    name = sc.next();
    birthDate = MyCalendar.convertDate(sc.next());
    test1 = sc.nextInt();
    test2 = sc.nextInt();
    test3 = sc.nextInt();
}

你在这里调用构造函数 -

int pos = Collections.binarySearch(studentList, new   Student(searchAdminNo));

当您在构造函数中阅读时，

searchAdminNo可能没有那么多令牌（由;分隔）。

Java中对象数组列表的二进制搜索

1 个答案: