Map map = new Hashmap();//創(chuàng)建一個(gè)map
map.put("key","value");//給map賦值
String vlaues = map.get("key");//獲取map中鍵值為“key”的值
system.out.println(vlaues );//輸出結(jié)果

// JDK源碼 
public V get(Object key) {
        Node<K,V> e;
        return (e = getNode(hash(key), key)) == null ? null : e.value;
}
 
final Node<K,V> getNode(int hash, Object key) {
        Node<K,V>[] tab; Node<K,V> first, e; int n; K k;
		//判斷hashtable是否為空，key對(duì)應(yīng)的tab[ ]是否為空
        if ((tab = table) != null && (n = tab.length) > 0 &&
            (first = tab[(n - 1) & hash]) != null) {
			//判斷第一個(gè)節(jié)點(diǎn)的hash，key是否相等
            if (first.hash == hash && // always check first node
                ((k = first.key) == key || (key != null && key.equals(k))))
                return first;
			//判斷下一個(gè)節(jié)點(diǎn)是否為空
            if ((e = first.next) != null) {
				//判斷是否是紅黑樹(shù)的節(jié)點(diǎn)，并遍歷查找元素
                if (first instanceof TreeNode)
                    return ((TreeNode<K,V>)first).getTreeNode(hash, key);
                do {
                    if (e.hash == hash &&
                        ((k = e.key) == key || (key != null && key.equals(k))))
                        return e;
                } while ((e = e.next) != null);
            }
        }
        return null;
    }