When I use MapEntry[] entry = (MapEntry[]) new Object[capacity],
it tells me java.lang.ClassCastException.
How can this happen? I am confused about this. (Since it seems I should do the casting because it's generic)
I found some tutorial and they were using like this:
table = new Entry[capacity];
(http://www.javamadesoeasy.com/2015/02/hashmap-custom-implementation.html)
it did not even do the casting.
My codes are below.
public class MyHashMap<K, V> {
private class MapEntry {
K key;
V value;
MapEntry next;
MapEntry(K key, V value) {
this.key = key;
this.value = value;
}
}
private int size = 0;
private int capacity;
MapEntry[] entry;
@SuppressWarnings("unchecked")
MyHashMap() {
capacity = 10;
entry = (MapEntry[]) new Object[capacity];
}
@SuppressWarnings("unchecked")
MyHashMap(int capacity) {
entry = (MapEntry[]) new Object[capacity];
}
public void put(K key, V value) {
int hash = hashCode(key);
MapEntry newNode = new MapEntry(key, value);
if (entry[hash % capacity] == null) {
entry[hash % capacity] = newNode;
} else {
if (key == entry[hash % capacity].key) {
entry[hash % capacity].value = value;
} else {
MapEntry nextNode = entry[hash % capacity].next;
while (nextNode != null) {
if (key == nextNode.key) {
nextNode.value = value;
return;
}
nextNode = nextNode.next;
}
nextNode = newNode;
}
}
}
public V get(K key) {
int hash = hashCode(key);
MapEntry node = entry[hash % capacity];
if (node == null) {
return null;
}
if (node.key == key) {
return node.value;
}
while (key != node.key) {
node = node.next;
if (node.key == key) {
return node.value;
}
}
return null;
}
public boolean contains(K key) {
return get(key) != null;
}
public int size() {
return size;
}
public void remove(K key) {
int hash = hashCode(key);
MapEntry node = entry[hash % capacity];
if (node == null) return;
if (key == node.key) {
entry[hash % capacity] = node.next;
}
MapEntry pre = node;
while (key != node.key) {
node = node.next;
if (key == node.key) {
pre.next = node.next;
return;
}
pre = pre.next;
}
}
private int hashCode(K key) {
return Math.abs(key.hashCode());
}
public void display(){
for(int i = 0; i < capacity; i++){
if(entry[i] != null){
MapEntry node = entry[i];
while(node != null){
System.out.print("{" + node.key + "=" + node.value + "}" + " ");
node = node.next;
}
}
}
}
public static void main(String[] args) {
MyHashMap<Integer, Integer> hashMapCustom = new MyHashMap<Integer, Integer>();
hashMapCustom.put(21, 12);
hashMapCustom.put(25, 121);
hashMapCustom.put(30, 151);
hashMapCustom.put(33, 15);
hashMapCustom.put(35, 89);
System.out.println("value corresponding to key 21="
+ hashMapCustom.get(21));
System.out.println("value corresponding to key 51="
+ hashMapCustom.get(51));
System.out.print("Displaying : ");
hashMapCustom.display();
System.out.print("Displaying : ");
hashMapCustom.display();
}
}
