01.HashMap源码学习整理思维导图

参考学习视频资料: http://www.mayikt.com/

/** * 基于数组实现HashMap * * @author zx * @date 2021年05月05日 13:37 */
public class ArrayHashMap<K, V> {

//先不考虑扩容 HashMap 初始容量为16. ；
// 第一次；当存放的值 16*0.75 =12(容量 * 0.75) 进行扩容，扩容后得到的容量大小为: 16<<1 = 32;
//第二次： 当存放的值32*0.75 = 25 进行扩容 ,扩容大小 32 << 1 = 64
private final Entry[] entries = new Entry[1000];
/** * 添加元素 * * @param k key值 * @param v value值 */
public void add(K k, V v) {

int index = hash(k);
Entry oldEntry = entries[index];
if (oldEntry == null) {

entries[index] = new Entry<>(k, v);
} else {

if (index == 0) {

entries[index] = new Entry<>(k, v);
}
oldEntry.next = new Entry<>(k, v);
}
}
/** * 根据key值获取对应的value * * @param k key值 * @return 返回对应key的value值 */
public V get(K k) {

int index = hash(k);
for (Entry oldEntry = entries[index]; oldEntry != null; oldEntry = oldEntry.next) {

//hashcode相同，我们需要比较内容值
if ((k == null && oldEntry.key == null) || oldEntry.key.equals(k)) {

return (V) oldEntry.value;
}
}
return null;
}
/** * 遍历Map */
public void list() {

if (entries == null) {

System.out.println("集合中没有存放元素，不能为遍历");
}
for (Entry entry : entries) {

if (entry != null) {

Entry temp = entry.next;
while (temp != null) {

System.out.println(temp.key + "---" + temp.value);
temp = temp.next;
}
System.out.println(entry.key + "---" + entry.value);
}
}
}
/** * 计算hash值 * * @param key key值 * @return hash值 */
static int hash(Object key) {

int h;
return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
}
private static class Entry<K, V> {

K key;
V value;
Entry<K, V> next;
public Entry(K key, V value) {

this.key = key;
this.value = value;
}
@Override
public String toString() {

return "Entry{" +
"key=" + key +
", value=" + value +
'}';
}
}
public static void main(String[] args) {

ArrayHashMap<Object, Object> map = new ArrayHashMap<>();
map.add(null, "null value");
map.add(null, "null value2");
map.add("a", "a is hashcode 97");
map.add(97, "97 is hashcode 97");
map.add(98, "98 is hashcode 98");
map.add("b", "b is hashcode 98");
System.out.println("------------------");
map.list();
System.out.println("------------------");
System.out.println(map.get(null));
System.out.println(map.get("a"));
System.out.println(map.get(97));
}
}