Integer.valueOf（）错误ArrayIndexOutOfBoundsException：

Question

String currentLine = reader.readLine();
while (currentLine != null)
{
  String[] studentDetail = currentLine.split("");

  String name = studentDetail[0];

  int number = Integer.valueOf(studentDetail[1]);
  currentLine = reader.readLine();
}

So I have a file like this:

   student1
   student16
   student6
   student9
   student10
   student15

When I run the program said: ArrayIndexOutOfBoundsException:1

the output should look like this:

   student1
   student6
   student9
   student10
   student11
   student15
   student16

Answer 1

Assuming all the lines start with student and end with a number, you can read all the lines and add them to a list and then sort the list by the number after student , then print each element. For example:

String currentLine;
List<String> test = new ArrayList<String>();
while ((currentLine = reader.readLine()) != null)
    test.add(currentLine());
test.stream()
    .sorted((s1, s2) -> Integer.parseInt(s1.substring(7)) - Integer.parseInt(s2.substring(7)))
    .forEach(System.out::println);

output:

student1
student6
student8
student9

If you don't want to use stream() and lambda , You can sort the list with a custom Comparator then loop through the list and print each element:

Collections.sort(test, new Comparator<String>() {
    @Override
    public int compare(String s1, String s2) {
        int n1 = Integer.parseInt(s1.substring(7));
        int n2 = Integer.parseInt(s2.substring(7));
        return n1-n2;
    }
});

Answer 2

First, program to the List interface instead of the ArrayList concrete type. Second, use a try-with-resources (or explicitly close your reader in a finally block). Third, I would use a Pattern (a regex ) and then a Matcher in the loop to look for "name" and "number". That might look something like,

List<Student> student = new ArrayList<>();
try (BufferedReader reader = new BufferedReader(new FileReader(new File(infile)))) {
    Pattern p = Pattern.compile("(\\D+)(\\d+)");
    String currentLine;
    while ((currentLine = reader.readLine()) != null) {
        Matcher m = p.matcher(currentLine);
        if (m.matches()) {
            // Assuming `Student` has a `String`, `int` constructor
            student.add(new Student(m.group(1), Integer.parseInt(m.group(2))));
        }
    }
} catch (FileNotFoundException fnfe) {
    fnfe.printStackTrace();
}

Finally, note that Integer.valueOf(String) returns an Integer (which you then unbox ). That is why I have used Integer.parseInt(String) here.

Answer 3

Your file must be like this

student 1
student 2
student 3

don't forget to add space character between student and number. And inside your iteration you must add this line: currentLine = reader.readLine(); you can split like this: String[] directoryDetail = currentLine.split(" "); instead of String[] directoryDetail = currentLine.split(""); because when you use String[] directoryDetail = currentLine.split(""); with student1 the result is a string array of String with length = 0