HashMap

javamadesoeasy

import java.lang.reflect.Array;

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[]) Array.newInstance(MapEntry.class, capacity);
    }

    @SuppressWarnings("unchecked")
    MyHashMap(int capacity) {
        entry =  (MapEntry[]) Array.newInstance(MapEntry.class, capacity);
    }

    public void put(K key, V value) {
        int hash = hashCode(key);
        MapEntry newNode = new MapEntry(key, value);
        MapEntry pre = entry[hash % capacity];
        if (entry[hash % capacity] == null) {
            entry[hash % capacity] = newNode;
            size++;
        } else {
            if (key == entry[hash % capacity].key) {
                entry[hash % capacity] = newNode;
            } else {
                MapEntry nextNode = entry[hash % capacity].next;
                while (nextNode != null) {
                    if (key == nextNode.key) {
                        nextNode = newNode;
                        return;
                    }
                    pre = pre.next;
                    nextNode = nextNode.next;
                }
                nextNode = newNode;
                pre.next = nextNode;
            }
        }
    }

    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 (node != null && key != node.key) {
            node = node.next;
            if (node == null) {
                return null;
            }
            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 (node == null) {
                return;
            }
            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("{" + "Key: " + node.key + " Value:" + node.value + "}" + " ");
                    node = node.next;
                }
           }
       }
       System.out.println();
    }

    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);
        hashMapCustom.put(11, 32);
        System.out.println("value corresponding to key 21 is :"
                     + hashMapCustom.get(21));
        System.out.println("value corresponding to key 51 is :"
                    + hashMapCustom.get(30));

        System.out.print("Displaying : ");
        hashMapCustom.display();
        hashMapCustom.remove(21);
        hashMapCustom.remove(51);

        System.out.print("Displaying : ");
        hashMapCustom.display();
    }
}