Thread: NullPointer exception error

Hello!

I'm wondering what I've done wrong with my code....It returns nullPonter exception and I don't know why, please help me.

 
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Scanner;
 
public class Naloga2 {
 
 
	 private static  int  m_cnt;
	 private static int  m_in[];
 
 
	 public static int Sort(int in [],int cnt)
	 {
		    int m_in[]=new int[cnt];
	        m_cnt = cnt;
 
	        for(int i=0;i<m_cnt;i++)
	        {
	                m_in[i]=in[i];
	        }
 
	        return mSort(0, m_cnt);
	 }
 
	  public static int mSort(int  ind, int  cnt)
	    {
	        int    tmp;
	        int  left, right;
 
	        if (cnt == 1) 
	        {
	            return 0;
	        }
 
	        left  = (cnt + 1) / 2;
	        right = cnt / 2;
 
	        if (cnt == 2) 
	        {
	            mDisplay(ind, 1, 1);
 
	            if (m_in[ind] > m_in[ind+1]) 
	            {
	                tmp = m_in[ind];
	                m_in[ind]= m_in[ind+1];
	                m_in[ind+1]= tmp;
	            }
 
	            mDisplay(ind, 2, 0);
 
	        } else {
	            mDisplay(ind, left, right);
 
	            mSort(ind, left);       // left
	            mSort(ind+left, right); //right
 
	            mOrder(ind, left, right);
 
	            mDisplay(ind, left + right, 0);
	        }
 
	        return 0;
	    }
 
	  public static int mOrder(int  ind, int  left, int  right)
	    {   
	        int   i, a, b;
	        int   tmp []=new int [left+right];
 
	        a = b = 0;
 
	        for (i = 0; i < (left+right); ++i) 
	        {
	            if ((m_in[ind+a] > m_in[ind+left+b] && b < right) || a >= left)
	            {
	                tmp[i] = m_in[ind+left+b];
	                ++b;
	            } 
	            else if (a < left)
	            { 
	                tmp[i] = m_in[ind+a];
	                ++a;
	            }
 
	        }
 
	        for(int x=0;x<(left+right);x++)
	        {
	                m_in[ind+x]=tmp[x];
	        }
 
 
 
 
	        return 0;
	    } 
 
	  public static void mDisplay(int  ind, int  left, int  right)
	    {
	       int   i, j;
 
	        for (i = 0; i < left; ++i) 
	        {
	            System.out.print(m_in[ind+i]+" ");
	        }    
 
	        if (right == 0) 
	        {
	            System.out.println();
	            return;
	        }
 
	        System.out.print("| ");
 
	        for (j = 0; j < right; ++j) 
	        {
	            System.out.print(m_in[ind+i+j]+" ");
	        }    
 
 
	        System.out.println();
	    }
 
 
 
		public static ArrayList<Integer> input(ArrayList<Integer> list,Scanner sc) {
 
			while(true)
			{
				if(sc.hasNextInt())
 
				{
					list.add(sc.nextInt());
				}
				else 
				{
					break;
				}
 
 
			}
 
			return (list);
		}
 
 
		public static int [] retTable(int [] table, ArrayList<Integer> list) {
 
 
			for(int i=0;i<list.size();i++)
			{
				table[i]=(int)list.get(i);
			}
 
 
			return (table);
		}	
 
 
 
 
 
		public static void main(String [] args) {
 
			String algorithm=args[0];
			Scanner sc = new Scanner(System.in);
 
 
			ArrayList<Integer> list = new ArrayList<Integer>();
			ArrayList<Integer> listNew = new ArrayList<Integer>();
 
			listNew=input(list,sc);
 
			int [] table = new int[listNew.size()];
			int [] tableNew = new int[listNew.size()];
 
			tableNew=retTable(table,listNew);
 
 
 
 
			if(algorithm.equals("QS"))
			{
				//izpisiSledQS(tabelaNova);	
			}
			else if(algorithm.equals("MS"))
			{
				Sort(tableNew,tableNew.length);
 
			}
			else
			{
				System.out.println("Pass sorting algorithm as argument.");
			}
 
 
 
 
 
 
 
 
		}
 
 
 
 
 
}

Of critical importance is your telling us which line throws this exception. When asking a question such as this, you'll *always* want to post the complete exception message and always want to indicate the line, possibly by obvious comment like // ******* NPE is thrown here! ******.

check out your first method Sort... did u mean to delcare another m_in array because your static int[] member is never being initialized and used correctly in the program