TaskOne

import java.io.*;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Objects;

public class TaskOne {

    private long[] sequence;

    public static void main(String[] args) {
        new TaskOne().start();
    }

    private void start() {
        System.out.println("введите имя файла в формате имя.txt. для выхода введите stop.");
        String input = getInput();
        if (checkIfNull(input)) {
            start();
        } else if ((input.equals("stop")) || input.equals("stop.")) {
            System.out.println("до свидания.");
        } else {
            readFromFile(input);
            Arrays.sort(sequence);
            try {
                System.out.println("90th percentile: " + percentile(sequence, 90));
                System.out.println("median: " + median(sequence));
                System.out.println("average: " + average(sequence));
                System.out.println("max: " + max(sequence));
                System.out.println("min: " + min(sequence));
                start();
            } catch (ArrayIndexOutOfBoundsException ex) {

            }
        }
    }

    private boolean checkIfNull(String input) {
        boolean isEmpty = input == null || input.trim().length() == 0;
        if (isEmpty) {
            return true;
        } else return false;
    }

    private void readFromFile(String fileName) {
        List<Integer> inputList = new ArrayList<>();
        try {
            BufferedReader reader = new BufferedReader(new FileReader(fileName));
            String number;
            if (reader.readLine() == null) {
                System.out.println("файл не должен быть пустым.");
                start();
            } else {
                while ((number = reader.readLine()) != null) {
                    inputList.add(Integer.valueOf(number));
                }
            }
            reader.close();
        } catch (FileNotFoundException ex) {
            System.out.println("нет такого файла.");
            start();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
        sequence = inputList.stream().filter(Objects::nonNull).mapToLong(i -> i).toArray();
    }

    private static String getInput() {
        String fileName = null;
        try {
            BufferedReader reader = new BufferedReader(
                    new InputStreamReader(System.in));
            fileName = reader.readLine();
            if (fileName.length() == 0) return null;
        } catch (IOException ex) {
            ex.printStackTrace();
        }
        return fileName;
    }

    private static long[] makeRandomArray(int length, int maxNum) {
        long[] array = new long[length];
        for (int i = 0; i < length; i++) {
            array[i] = (long) (Math.random() * (maxNum + 1));
        }
        return array;
    }

    private static long average(long[] sequence) {
        long sum = 0;
        for (long number : sequence)
            sum += number;
        return sum / sequence.length;
    }

    private static long max(long[] sequence) {
        return sequence[sequence.length - 1];
    }

    private static double median(long[] sequence) {
        int middle = sequence.length / 2;
        if (sequence.length % 2 == 1) {
            return sequence[middle];
        } else {
            return ((sequence[middle - 1] / 2) + (sequence[middle]) / 2);
        }
    }

    private static long min(long[] sequence) {
        return sequence[0];
    }

    private static long percentile(long[] sequence, int rank) {
        double x = (double) rank / 100;
        int index = (int) Math.round((sequence.length) * x);
        return sequence[index - 1];
    }
}