null pointer exception error :(
package com.codegym.task.task09.task0930;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.*;
/*
Task about algorithms
*/
public class Solution {
public static void main(String[] args) throws Exception {
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
ArrayList<String> list = new ArrayList<String>();
while (true) {
String s = reader.readLine();
if (s.isEmpty()) break;
list.add(s);
}
String[] array = list.toArray(new String[list.size()]);
sort(array);
for (String x : array) {
System.out.println(x);
}
}
public static void sort(String[] array) {
ArrayList<String> words = new ArrayList<String>();
ArrayList<Integer> numbers = new ArrayList<Integer>();
// int a = Integer.parseInt(s);
for(String S : array)
{
if(isNumber(S)){
numbers.add(Integer.parseInt(S));
}
else
{
words.add(S);
}}
Collections.sort(numbers);
Collections.reverse(numbers);
for(int i=0; i<words.size(); i++){
for(int j=i+1; j<words.size(); j++){
if(isGreaterThan(words.get(i),words.get(j))){
String a = words.get(i);
String b = words.get(j);
String temp = a;
words.add(i,b);
words.add(i+1,a);
}
}
}// write your code here
int x=0;
int y =0;
for(int i=0; i<array.length; i++){
if(isNumber(array[i])){
array[i]= String.valueOf(numbers.get(x));
x++;
}
else
{
array[i] = words.get(y);
y++;
} }
}
// String comparison method: 'a' is greater than 'b'
public static boolean isGreaterThan(String a, String b) {
return a.compareTo(b) > 0;
}
// Is the passed string a number?
public static boolean isNumber(String s) {
if (s.length() == 0) return false;
char[] chars = s.toCharArray();
for (int i = 0; i < chars.length; i++) {
char c = chars[i];
if ((i != 0 && c == '-') // The string contains a hyphen
|| (!Character.isDigit(c) && c != '-') // or is not a number and doesn't start with a hyphen
|| (i == 0 && c == '-' && chars.length == 1)) // or is a single hyphen
{
return false;
}
}
return true;
}
}