Null Pointer Exception & Data Has Been Changed??
Please Help
package com.codegym.task.task09.task0930;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
/*
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> numbers = new ArrayList<String>();
ArrayList<String> words = new ArrayList<String>();
for (String x : array) {
if (isNumber(x)) {
numbers.add(x);
}
else {
words.add(x);
}
}
for (int i = 0; i <numbers.size(); i++) {
String a = numbers.get(i);
String b = numbers.get(i+1);
if (isGreaterThan(a,b)){
String temp = a;
a = b;
b = temp;
}
}
for (int i = 0; i <words.size(); i++) {
String a = words.get(i);
String b = words.get(i+1);
if (isGreaterThan(a,b)){
String temp = a;
a = b;
b = temp;
}
}
for (int i = 0; i <array.length; i++) {
if (isNumber(array[i])) {
array[i] = numbers.get(0);
numbers.remove(0);
}
else {
array[i] = numbers.get(0);
words.remove(0);
}
}
}
// 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;
}
}