HashMap理解(1)-知识积累

Map map = new HashMap();
map.put("张三",10);
map.put("李四",20);
Integer age=map.get("张三")；

接口  Map,Cloneable, Serializable 
                    |
            抽象类 AbstractMap
                    |
            具体实现类 HashMap                                                  

final float loadFactor;

static final float DEFAULT_LOAD_FACTOR = 0.75f;

public HashMap() {

      this.loadFactor = DEFAULT_LOAD_FACTOR; // all other fields defaulted
}

public V put(K key, V value) {
        return putVal(hash(key), key, value, false, true);
}

//传入参数为 （774882,"张三",10,false,true)
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
               boolean evict) {

    /**
    *  Node{  
    *     final int hash；
    *     final K key；
    *     V value;
    *     Node next;
    *  }
    */
    Node[] tab; 
    Node p; 
    int n,i;

    /**
    *以上是该方法四个局部变量
    *重点关注该方法对该实体类全局变量的修改
    *该类中涉及到全局信息的有
    *    static final int TREEIFY_THRESHOLD = 8;
    *    transient Node[] table;
    *    transient int modCount;
    *    transient int size;
    *    int threshold;
    */

    //全局变量table初始化时赋值null
    if ((tab = table) == null || (n = tab.length) == 0)  
        //调用resize方法 n为16即tab数组初始化长度16 该方法执行时执行了    table = (Node[])new Node[16];
        n = (tab = resize()).length;  
        //p=tab[2]==null 
    if ((p = tab[i = (n - 1) & hash]) == null)
        //tab[2]=Node{hash:774882,key:"张三",value:10,next:null} 即table[2]=Node{hash:774882,key:"张三",value:10,next:null}
        tab[i] = newNode(hash, key, value, null);
    # else {//数组空间未被占用
    #     Node e; K k;
    #     if (p.hash == hash &&
    #         ((k = p.key) == key || (key != null && key.equals(k))))
    #         e = p;
    #     else if (p instanceof TreeNode)
    #         e = ((TreeNode)p).putTreeVal(this, tab, hash, key, value);
    #     else {
    #         for (int binCount = 0; ; ++binCount) {
    #             if ((e = p.next) == null) {
    #                 p.next = newNode(hash, key, value, null);
    #                 if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
    #                     treeifyBin(tab, hash);
    #                 break;
    #             }
    #             if (e.hash == hash &&
    #                 ((k = e.key) == key || (key != null && key.equals(k))))
    #                 break;
    #             p = e;
    #         }
    #     }
    #     if (e != null) { // existing mapping for key
    #         V oldValue = e.value;
    #         if (!onlyIfAbsent || oldValue == null)
    #             e.value = value;
    #         afterNodeAccess(e);
    #         return oldValue;
    #     }
    # }
    ++modCount;//该值为1
    if (++size > threshold)//size=1  threshold该值在resize方法中  threshold=16*0.75=12
        resize();
    afterNodeInsertion(evict); // Callbacks to allow LinkedHashMap post-actions 本类无方法体
    return null;//张三 10被存储到table数组的第2位置中
}

//传入参数为 （842049,"李四",20,false,true)
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
               boolean evict) {

    /**
    *  Node{  
    *     final int hash；
    *     final K key；
    *     V value;
    *     Node next;
    *  }
    */
    Node[] tab; 
    Node p; 
    int n,i;

    /**
    *以上是该方法四个局部变量
    *重点关注该方法对该实体类全局变量的修改
    *该类中涉及到全局信息的有
    *    static final int TREEIFY_THRESHOLD = 8;
    *    transient Node[] table;
    *    transient int modCount;
    *    transient int size;
    *    int threshold;
    */

    //此时tab={；；；table[2]=Node{hash:774882,key:"张三",value:10,next:null}；；；} n=16
    if ((tab = table) == null || (n = tab.length) == 0)  
        //不为null跳过初始化
        n = (tab = resize()).length;   
    if ((p = tab[i = (n - 1) & hash]) == null) //tab[1]=null
        //tab[1]=Node{hash:842049,key:"李四",value:20,next:null} 即table[1]=Node{hash:842049,key:"李四",value:20,next:null}
        tab[i] = newNode(hash, key, value, null);
    # else {//数组空间未被占用 下次查看该分支 先研究一下链表和树
    #     Node e; K k;
    #     if (p.hash == hash &&
    #         ((k = p.key) == key || (key != null && key.equals(k))))
    #         e = p;
    #     else if (p instanceof TreeNode)
    #         e = ((TreeNode)p).putTreeVal(this, tab, hash, key, value);
    #     else {
    #         for (int binCount = 0; ; ++binCount) {
    #             if ((e = p.next) == null) {
    #                 p.next = newNode(hash, key, value, null);
    #                 if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
    #                     treeifyBin(tab, hash);
    #                 break;
    #             }
    #             if (e.hash == hash &&
    #                 ((k = e.key) == key || (key != null && key.equals(k))))
    #                 break;
    #             p = e;
    #         }
    #     }
    #     if (e != null) { // existing mapping for key
    #         V oldValue = e.value;
    #         if (!onlyIfAbsent || oldValue == null)
    #             e.value = value;
    #         afterNodeAccess(e);
    #         return oldValue;
    #     }
    # }
    ++modCount;//该值为2
    if (++size > threshold)//size=2  threshold=16*0.75=12//下次查看该分支 超过阈值扩容
        resize();
    afterNodeInsertion(evict); // Callbacks to allow LinkedHashMap post-actions 本类无方法体
    return null;//李四 20被存储到table数组的第1位置中
}

public V get(Object key) {
        Node e;
        //获取该位置的Node节点，直接获取该value值 返回10
        return (e = getNode(hash(key), key)) == null ? null : e.value;
}

//参数（774882,"张三"）
final Node getNode(int hash, Object key) {
        Node[] tab;
        Node first, e; 
        int n; 
        K k;
        /**
        *table[1]=Node{hash:842049,key:"李四",value:20,next:null}
        *table[2]=Node{hash:774882,key:"张三",value:10,next:null}
        */
        if ((tab = table) != null && (n = tab.length) > 0 &&
                (first = tab[(n - 1) & hash]) != null) {   //first=table[1]=Node{;;;"张三"}
            if (first.hash == hash && 
                ((k = first.key) == key || (key != null && key.equals(k))))
                return first;//first.next==null 直接返回该Node 该位置无链表或树
            if ((e = first.next) != null) {
                if (first instanceof TreeNode)
                    return ((TreeNode)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;
    }