Hey, i have the following code, it makes a map, but i keep getting a null pointer exception in my remove method. Anyone help me??? Pls
import java.lang.Math;
class Node{
Object key;
Object data;
Node next;
public Node (Object k, Object d, Node n){
key = k;
data = d;
next = n;
}//end of constructor
}// end of node class
public class Map{
public Map (int cap){
capacity = cap;
map = new Node[capacity];
int size=0;
int arraySize=0;
int placement = 0;
}//initialiser constructor
public Map () {
capacity = 11;
map = new Node[capacity];
int placement = 0;
int size = 0;
int arraySize =0;
}
private static int arraySize;
private static int capacity;
private static Node map[];
private static Node head;
private static Node oldHead;
private static int size;
private static int placement;
public static Object[] keys (){
System.out.println("KEYS METHOD ENTERED"); System.out.println();
Object arrayB[] = new Object[capacity];
int counterB = 0;
for (int counter = 0; counter < capacity ; counter++){
if (map[counter] != null){//list stored here
for (Node p = map[counter]; p != null; p = p.next){
arrayB[counterB] = p.key;
counterB++;
}//end of for
}//end of if
}//end of for
System.out.println("KEYS METHOD EXITED"); System.out.println();
return arrayB;
}//end of method
public static void remove(Object key){
for(int counter = 0; counter< capacity; counter ++){
// controls movement along array
if(map[counter].key!=null){
// 1) Node could be first in list
// 2) Further into the list
// 3) Not exist in this list, or the Map at all
// 1) If the node is first in the list:
if(map[counter].data == key){
// a) There are no following nodes after this one
// b) There is a list following on.
//a
if(map[counter].next == null){
map[counter]=null;
}
//b
if(map[counter].next != null){
map[counter] = map[counter].next;
}
}//end of if
else{//the node is further in
Node prev = map[counter]; System.out.println("Got here fucker");
for(Node q = map[counter]; q!= null; q=q.next){
//established that not first node, so started at next one
if(q.data == key){// must remove
if(q.next ==null){// then this is the last node in the list
prev.next = null; // node is removed by garbage collector
}
if(q.next!=null){//this is in the middle of a list
prev.next = q.next; // node removed
}
}
else{
prev = q; // other increments controlled by for loop
}
}//end of for
}//end of else
}//end of else
}//end of for loop
}
public static Object get (Object key) {
Object returnKey = "";//done to avoid null being printed out
for(int counter = 0; counter < capacity; counter ++){
if(map[counter] != null){ //there is a list here
for(Node scan = map[counter]; scan!= null; scan = scan.next){
if(scan.data == key){
returnKey = scan.data;
}
}//end of for loop for linked list
}//end of != null if
}//end of for loop
return returnKey;
}//end of get method
public static Object put (Object key, Object value){
Object toReturn = null;
/** System.out.println("PUT METHOD ENTERED"); System.out.println();
System.out.println("Current Key is "+key); */
placement = key.hashCode () % capacity;
/** System.out.println("placement " + placement);
System.out.println("Capacity " + capacity); */
if (map[placement] != null){//means we won't have to rehash as not adding to a new slot in array
System.out.println(" != null entered with key "+ key);
Node scanner = map[placement];
Node prev = scanner; //toReturn remains null, as nothing before it
for(scanner=map[placement]; scanner!=null; scanner = scanner.next){
if(scanner.next == null){//time to add
prev.next = new Node(key, value, null);
toReturn = prev.data;//this is where we added on
}
if(scanner.next!= null){//must keep going thorough the list, so move to scanner, done by for loop
//prev = scanner;
prev = scanner;
}
}
size++;
System.out.println(" != null if exited");
System.out.println();
}//end of if 1
if (map[placement] == null){//then we are about to add to a new section in the array, we must make sure we do not
// exceed the load factor
if ((arraySize + 1) < (Math.floor(capacity * 0.75))){//no rehash is needed
map[placement] = new Node (key, value, null);
arraySize++;
System.out.println(arraySize);
size++;
System.out.println(" Came to no rehash if in put method");
}//end of size 1 if
else{
Object tempKey = key; //don't want these to change during rehash
Object tempVal = value;
Map.rehash();
Map.put (tempKey, tempVal);
arraySize++;
System.out.println(" Came to rehash if");
}//end of if 2
}//end of if 2
return toReturn;
}//end of method
public static int size (){
return size;
}
public static void rehash (){
System.out.println("REHASH METHOD ENTERED"); System.out.println();
Object toBeHashed[] = Map.keys ();
size = 0; // no more objects in the array
int oldCapacity = capacity;
capacity = capacity * 2; arraySize =0;
Node temp[] = new Node[capacity];//because we cannot change the size of the old array
map =temp;
for (int j = 0; j < oldCapacity; j++)
{
if(toBeHashed[j]!=null){
Map.put (toBeHashed[j], toBeHashed[j]);
}
}
System.out.println("REHASH METHOD EXITED");
System.out.println();
}// end of rehash method
} // end of class
Tester Class:
public class A4Test {
public static void main(
String a[] ) {
String s[]={"ape","bat","cat","dog","fox","gnu","hog","pig"};
Map m = new Map(3); // init capacity 3
for( int i = 0; i < s.length; i++ ){
m.put( s[i], s[i] );
}
Object b[] = m.keys();
m.remove("ape");
for( int i = 0; i < b.length; i++ )
System.out.print( ((String)m.get( b[i] )) + " ");
System.out.println(Map.size());
System.out.println();
}
}
Th
