TreeMap通过Comparator/Comparable实现自定义排序
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
Comparator<? super K> cpr = comparator;
if (cpr != null) { //如果比较器不为空，则通过比较器来比较key的大小
do {
parent = t;
cmp = cpr.compare(key, t.key);
if (cmp < 0) // 比较的结果小于0，放在左子节点
t = t.left;
else if (cmp > 0) // 比较的结果大于0，放在右子节点
t = t.right;
else
return t.setValue(value); // 结果等于零，代表key值相等，覆盖value值
} while (t != null);
}
else { // 当没有传入Comparator时，就使用key对象的compareTo方法
if (key == null)
throw new NullPointerException();
@SuppressWarnings("unchecked")
Comparable<? super K> k = (Comparable<? super K>) key;
do {
parent = t;
cmp = k.compareTo(t.key);
if (cmp < 0)
t = t.left;
else if (cmp > 0)
t = t.right;
else
return t.setValue(value);
} while (t != null);
}
Entry<K,V> e = new Entry<>(key, value, parent);
if (cmp < 0)
parent.left = e;
else
parent.right = e;
fixAfterInsertion(e);
size++;
modCount++;
return null;
}