public class MyArrayList<E> {   private int capacity = 10;   private int size = 0;   private E[] values = null;    @SuppressWarnings("unchecked")   public MyArrayList() {     values = (E[]) new Object[capacity];   }    @SuppressWarnings("unchecked")   public MyArrayList(int capacity) {     this.capacity = capacity;     values = (E[]) new Object[this.capacity];   }    public void put(E e) {     if (e == null) {       throw new RuntimeException("The value should not be null.");     }     if (size >= capacity) {       enlargeCapacity();     }     values[size] = e;     size++;   }    public E get(int index) {     if (index >= size) {       throw new RuntimeException("The index:" + index + " is out of band.");     }     return values[index];   }    public void remove(int index) {     if (index >= size) {       throw new RuntimeException("The index:" + index + " is out of band.");     }     for (int i = index; i < size - 1; i++) {       values[i] = values[i + 1];     }     values[size - 1] = null;     size--;   }    @SuppressWarnings("unchecked")   private void enlargeCapacity() {     capacity = capacity * 2;     E[] tmpValues = (E[]) new Object[capacity];     System.arraycopy(values, 0, tmpValues, 0, size);     values = tmpValues;   }    public String toString() {     StringBuilder sb = new StringBuilder();     sb.append("[");     for (int i = 0; i < size; i++) {       sb.append(values[i]).append(",");     }     if (size > 0) {       sb.deleteCharAt(sb.length() - 1);     }     sb.append("]");     return sb.toString();   }    /**    * @param args    */   public static void main(String[] args) {     MyArrayList<String> myList = new MyArrayList<String>();     myList.put("1");     myList.put("2");     myList.put("3");     myList.put("4");     myList.put("5");     myList.put("6");     myList.put("7");     myList.put("8");     myList.put("9");     myList.remove(7);     System.out.println(myList.toString());   }  } 

public class MyHashMap<K, V> {   //initialization capacity   private int capacity = 10;   //total entities   private int size = 0;   private Entity<K, V>[] entities = null;    @SuppressWarnings("unchecked")   public MyHashMap() {     entities = new Entity[capacity];   }    public void put(K key, V value) {     if (key == null) {       throw new RuntimeException("The key is null");     }     reHash();     Entity<K, V> newEntity = new Entity<K, V>(key, value);     put(newEntity, this.entities, this.capacity);   }    private void put(Entity<K, V> newEntity, Entity<K, V>[] entities, int capacity) {     int index = newEntity.getKey().hashCode() % capacity;     Entity<K, V> entity = entities[index];     Entity<K, V> firstEntity = entities[index];     if (entity == null) {       entities[index] = newEntity;       size++;     } else {       if (newEntity.getKey().equals(entity.getKey())) {//Find the same key for the first entity, if find then replace the old value to new value         newEntity.setNext(entity.getNext());         newEntity.setPre(entity.getPre());         if (entity.getNext() != null) {           entity.getNext().setPre(newEntity);         }         entities[index] = newEntity;       } else if (entity.getNext() != null) {         while (entity.getNext() != null) {//Find the same key for all the next entity, if find then replace the old value to new value           entity = entity.getNext();           if (newEntity.getKey().equals(entity.getKey())) {             newEntity.setPre(entity.getPre());             newEntity.setNext(entity.getNext());             if (entity.getNext() != null) {               entity.getNext().setPre(newEntity);             }             entities[index] = newEntity;             return;           }         }         //Cannot find the same key, then insert the new entity at the header         newEntity.setNext(firstEntity);         newEntity.setPre(firstEntity.getPre());         firstEntity.setPre(newEntity);         entities[index] = newEntity;         size++;       } else {         //Cannot find the same key, then put the new entity in head         newEntity.setNext(firstEntity);         firstEntity.setPre(newEntity);         entities[index] = newEntity;         size++;       }     }   }    public V get(K key) {     if (key == null) {       throw new RuntimeException("The key is null");     }     int index = key.hashCode() % capacity;     Entity<K, V> entity = entities[index];     if (entity != null) {       if (entity.getKey().equals(key)) {         return entity.getValue();       } else {         entity = entity.getNext();         while (entity != null) {           if (entity.getKey().equals(key)) {             return entity.getValue();           }           entity = entity.getNext();         }       }      }     return null;   }    public void remove(K key) {     if (key == null) {       throw new RuntimeException("The key is null");     }     int index = key.hashCode() % capacity;     Entity<K, V> entity = entities[index];     if (entity != null) {       if (entity.getKey().equals(key)) {         if (entity.getNext() != null) {//remove the first entity           entity.getNext().setPre(entity.getPre());           entities[index] = entity.getNext();           entity = null;         } else {//empty this index           entities[index] = null;         }         size--;       } else {         entity = entity.getNext();         while (entity != null) {           if (entity.getKey().equals(key)) {             if (entity.getNext() != null) {               entity.getPre().setNext(entity.getNext());               entity.getNext().setPre(entity.getPre());               entity = null;             } else {               //release the found entity               entity.getPre().setNext(null);               entity = null;             }             size--;             return;           }           entity = entity.getNext();         }       }     }   }    public String toString() {     StringBuilder sb = new StringBuilder();     for (int i = 0; i < capacity; i++) {       sb.append("index=").append(i).append("[");       boolean hasEntity = false;       Entity<K, V> entity = entities[i];       if (entity != null) {         hasEntity = true;       }       while (entity != null) {         sb.append("[").append(entity.getKey()).append("=").append(entity.getValue()).append("]").append(",");         entity = entity.getNext();       }       if (hasEntity) {         sb.deleteCharAt(sb.length() - 1);       }       sb.append("]/n");     }     return sb.toString();   }    /**    * Simple re-hash strategy, if the size is bigger than capacity, then do re-hash action    */   private void reHash() {     if (size >= capacity) {       int newCapacity = capacity * 2;       @SuppressWarnings("unchecked")       Entity<K, V>[] newEntities = new Entity[newCapacity];       for (int i = 0; i < capacity; i++) {         Entity<K, V> entity = entities[i];         while (entity != null) {           put(entity, newEntities, newCapacity);           entity = entity.getNext();         }       }       this.capacity = newCapacity;       this.entities = newEntities;     }   }    public static void main(String[] args) {     MyHashMap<String, String> map = new MyHashMap<String, String>();     map.put("one", "1");     map.put("two", "2");     map.put("three", "3");     map.put("four", "4");     map.put("five", "5");     map.put("six", "6");     map.put("seven", "7");     map.put("eight", "8");     map.put("nine", "9");     map.put("ten", "10");     System.out.println(map.get("one"));     System.out.println(map.get("two"));     System.out.println(map.get("three"));     System.out.println(map.get("four"));     System.out.println(map.get("five"));     System.out.println(map.get("six"));     System.out.println(map.get("seven"));     System.out.println(map.get("eight"));     System.out.println(map.get("nine"));     System.out.println(map.get("ten"));     System.out.println(map.toString());      map.remove("nine");     map.remove("three");     System.out.println(map.get("one"));     System.out.println(map.get("two"));     System.out.println(map.get("three"));     System.out.println(map.get("four"));     System.out.println(map.get("five"));     System.out.println(map.get("six"));     System.out.println(map.get("seven"));     System.out.println(map.get("eight"));     System.out.println(map.get("nine"));     System.out.println(map.get("ten"));     System.out.println(map.toString());   } }  class Entity<K, V> {   private K key;   private V value;   private Entity<K, V> pre;   private Entity<K, V> next;    public Entity(K key, V value) {     this.key = key;     this.value = value;   }    public K getKey() {     return key;   }    public void setKey(K key) {     this.key = key;   }    public V getValue() {     return value;   }    public void setValue(V value) {     this.value = value;   }    public Entity<K, V> getPre() {     return pre;   }    public void setPre(Entity<K, V> pre) {     this.pre = pre;   }    public Entity<K, V> getNext() {     return next;   }    public void setNext(Entity<K, V> next) {     this.next = next;   }  }