Java - Ayuda Urgente MergeSort

Amigos, necesito presentar mañana 19-05-2010 el codigo mergesort en la universidad pero resulta que me arroja el siguiente error al momento de ingresar el numero en el subindice 0, por favor el que me pueda ayudar mandar un correo en forma urgente a [email protected] , error es el siguiente: Exception in thread "main" java.lang.NullPointerException at MergeSort.main(MergeSort.java:16)

Este es el codigo

import java.io.*;
public class MergeSort {
private static int[] arrayEntrada;

public static void main(String args[]) throws IOException{

BufferedReader bf;
bf =new BufferedReader(new InputStreamReader(System.in));
int subindice = 0;

System.out.println("Cuantos valores desea ingresar: ");
subindice=Integer.parseInt(bf.readLine());

for (int i=0;i < subindice;i++){

System.out.println("Ingrese valor para la Subindice " + i + ": ");
arrayEntrada[i]=Integer.parseInt(bf.readLine());
}

mergeSort(arrayEntrada); //llamada al metodo mergeSort
System.out.println("Este es el ordenamiento de los numeros");
for (int i=0;i < arrayEntrada.length;i++){
System.out.println(arrayEntrada[i]+" ");
}
}
public static void mergeSort( int a[ ]){
int tmpArray[] = new int[ a.length ];

mergeSort( a, tmpArray, 0, a.length - 1 );
}
private static void mergeSort( int a[ ], int tmpArray[],int left, int right ){
if( left < right )
{
int center = ( left + right ) / 2;
mergeSort( a, tmpArray, left, center );
mergeSort( a, tmpArray, center + 1, right );
merge( a, tmpArray, left, center + 1, right );
}
}

private static void merge( int a[ ],int tmpArray[],int leftPos, int rightPos, int rightEnd){
int leftEnd = rightPos - 1;
int tmpPos = leftPos;
int numElements = rightEnd - leftPos + 1;


while( leftPos <= leftEnd && rightPos <= rightEnd ){
if( a[ leftPos ]<( a[ rightPos ] ) ){
tmpArray[ tmpPos++ ] = a[ leftPos++ ];
}
else{
tmpArray[ tmpPos++ ] = a[ rightPos++ ];
}
}
while( leftPos <= leftEnd ){f
tmpArray[ tmpPos++ ] = a[ leftPos++ ];
}
while( rightPos <= rightEnd ){
tmpArray[ tmpPos++ ] = a[ rightPos++ ];
}

for( int i = 0; i < numElements; i++, rightEnd-- ){
a[ rightEnd ] = tmpArray[ rightEnd ];
}
}
}

http://java.sun.com/docs/books/tutorial/java/nutsandbolts/arrays.html

tre falto inicializar arrayEtrada en este ejemplo te e cambiado por la clase vector que es de tamaño dinamico



import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Vector;

/**
*
* @author Aitor
*/
public class MergeSort {

private static Vector arrayEntrada=new Vector(); //faltava inicializar

public static void main(String args[]) throws IOException {

BufferedReader bf;
bf = new BufferedReader(new InputStreamReader(System.in));
int subindice = 0;

System.out.println("Cuantos valores desea ingresar: ");
subindice = Integer.parseInt(bf.readLine());

for (int i = 0; i < subindice; i++) {

System.out.println("Ingrese valor para la Subindice " + i + ": ");
arrayEntrada.add(Integer.parseInt(bf.readLine()));
}

mergeSort(arrayEntrada); //llamada al metodo mergeSort
System.out.println("Este es el ordenamiento de los numeros");
for (int i = 0; i < arrayEntrada.size(); i++) {
System.out.println(arrayEntrada.elementAt(i));
}
}

public static void mergeSort(Vector a) {
int tmpArray[] = new int[a.size()];

mergeSort(a, tmpArray, 0, a.size() - 1);
}

private static void mergeSort(Vector a, int tmpArray[], int left, int right) {
if (left < right) {
int center = (left + right) / 2;
mergeSort(a, tmpArray, left, center);
mergeSort(a, tmpArray, center + 1, right);
merge(a, tmpArray, left, center + 1, right);
}
}

private static void merge(Vector a, int tmpArray[], int leftPos, int rightPos, int rightEnd) {
int leftEnd = rightPos - 1;
int tmpPos = leftPos;
int numElements = rightEnd - leftPos + 1;

while (leftPos <= leftEnd && rightPos <= rightEnd) {

Object l=a.elementAt(leftPos);
Object t=a.elementAt(rightPos);
if (Integer.parseInt(l.toString()) < Integer.parseInt(t.toString())) {
tmpArray[tmpPos++] = Integer.parseInt(a.elementAt(leftPos++).toString());
} else {
tmpArray[tmpPos++] =Integer.parseInt(a.elementAt(rightPos++).toString());
}
}
while (leftPos <= leftEnd) {
tmpArray[tmpPos++] = Integer.parseInt(a.elementAt(leftPos++).toString());
}
while (rightPos <= rightEnd) {
tmpArray[tmpPos++] = Integer.parseInt(a.elementAt(rightPos++).toString());
}

for (int i = 0; i < numElements; i++, rightEnd--) {
a.setElementAt(tmpArray[rightEnd], rightEnd);
}
}
}

este es tu ejemplo gastando un int [] arrayEntrada que lo inicializo al numero de elemetos que va a ordenar

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

/**
*
* @author Aitor
*/
public class MergeSort {

private static int[] arrayEntrada;

public static void main(String args[]) throws IOException {

BufferedReader bf;
bf = new BufferedReader(new InputStreamReader(System.in));
int subindice = 0;

System.out.println("Cuantos valores desea ingresar: ");
subindice = Integer.parseInt(bf.readLine());
arrayEntrada=new int[subindice]; // inicializacion!!!

for (int i = 0; i < subindice; i++) {

System.out.println("Ingrese valor para la Subindice " + i + ": ");
arrayEntrada[i] = Integer.parseInt(bf.readLine());
}

mergeSort(arrayEntrada); //llamada al metodo mergeSort
System.out.println("Este es el ordenamiento de los numeros");
for (int i = 0; i < arrayEntrada.length; i++) {
System.out.println(arrayEntrada[i] + " ");
}
}

public static void mergeSort(int a[]) {
int tmpArray[] = new int[a.length];

mergeSort(a, tmpArray, 0, a.length - 1);
}

private static void mergeSort(int a[], int tmpArray[], int left, int right) {
if (left < right) {
int center = (left + right) / 2;
mergeSort(a, tmpArray, left, center);
mergeSort(a, tmpArray, center + 1, right);
merge(a, tmpArray, left, center + 1, right);
}
}

private static void merge(int a[], int tmpArray[], int leftPos, int rightPos, int rightEnd) {
int leftEnd = rightPos - 1;
int tmpPos = leftPos;
int numElements = rightEnd - leftPos + 1;

while (leftPos <= leftEnd && rightPos <= rightEnd) {
if (a[leftPos] < (a[rightPos])) {
tmpArray[tmpPos++] = a[leftPos++];
} else {
tmpArray[tmpPos++] = a[rightPos++];
}
}
while (leftPos <= leftEnd) {
tmpArray[
tmpPos++ ] = a[leftPos++];
}
while (rightPos <= rightEnd) {
tmpArray[tmpPos++] = a[rightPos++];
}

for (int i = 0; i < numElements; i++, rightEnd--) {
a[rightEnd] = tmpArray[rightEnd];
}
}
}