Map总结

treeMap

//首次添加是返回null,覆盖则返回原有的值public V put(K key, V value) {        Entry<K,V> t = root;        if (t == null) {            compare(key, key); // type (and possibly null) check            root = new Entry<>(key, value, null);            size = 1;            modCount++;            return null;        }        int cmp;        Entry<K,V> parent;        // split comparator and comparable paths// 构造函数默认传进来的，一般没有传，则走下面的else        Comparator<? super K> cpr = comparator;        if (cpr != null) {            do {                parent = t;                cmp = cpr.compare(key, t.key);                if (cmp < 0)                    t = t.left;                else if (cmp > 0)                    t = t.right;                else                    return t.setValue(value);            } while (t != null);        }        else {            if (key == null)                throw new NullPointerException();//拿到key的compareble            @SuppressWarnings("unchecked")                Comparable<? super K> k = (Comparable<? super K>) key;            do {//t在以第一次循环的时候为root，也就是从root开始遍历                parent = t;                cmp = k.compareTo(t.key);                if (cmp < 0)                    t = t.left;                else if (cmp > 0)                    t = t.right;                else//表示已经添加过，则覆盖原有的                    return t.setValue(value);            } while (t != null);        }        Entry<K,V> e = new Entry<>(key, value, parent);//此时的parent就是找到的最后的一个节点        if (cmp < 0)            parent.left = e;        else            parent.right = e;        fixAfterInsertion(e);        size++;        modCount++;        return null;    }//取值的时候也是从root节点就行遍历final Entry<K,V> getEntry(Object key) {        // Offload comparator-based version for sake of performance        if (comparator != null)            return getEntryUsingComparator(key);        if (key == null)            throw new NullPointerException();        @SuppressWarnings("unchecked")            Comparable<? super K> k = (Comparable<? super K>) key;        Entry<K,V> p = root;        while (p != null) {            int cmp = k.compareTo(p.key);            if (cmp < 0)                p = p.left;            else if (cmp > 0)                p = p.right;            else                return p;        }        return null;    }