ArrayList and HashMap
The storage of ArrayList is an array.
The storage of HashMap is an array plus a linked list.
The following MyArrayList and MyHashMap are not used in actual work. The most likely thing to use is to interview and find a job and fool others. Although it is not useful at work, it does not mean it is useless. It can help us understand their implementation principles. After the implementation is completed, we will carefully check the source code in the JDK and we will find out where other people can learn in their implementation.
MyArrayList
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()); } } MyHashMap
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; } }Thank you for reading, I hope it can help you. 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