java - 从TreeMap克隆对象中删除元素不会从java中的主treemap对象中删除

Question

I read the following logic about TreeMap :

The TreeMap.clone() method returns the shallow copy of the TreeMap instance. In the shallow copy, object B points to object A location in memory. In other words, both object A and B are sharing the same elements. The keys and values themselves are not cloned.

Considering this correct, I made a program as per the link problem in which I removed an element from the treemap cloned object and my expectation was that this element must have been removed from main treemap object too but it didn't happen. I checked the key's hashcode too for both object but it was the same. Can someone please let me know, a shallow copy is something different in TreeMap or my understanding is something incorrect? Jdk - 1.8

Answer 1

Your understanding is somewhat incorrect (from my pov..sry!:)

My understanding is "key and values are same", but the cloned maps are not (same) ! And being part of a map is an information, which nor the key nor the value "knows about", but only the maps/containers... and this information is (copied &) owned by each map, after cloning.

I would agree with your misunderstanding / observation, if you would have checked the Map.Entry<K, V> s ... (these are also unknown to the underlying keys & values).

And after cloning, you/someone must ensure it, if you want the clones to be synchronized .

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If you indeed want "two references" of the same map (the expected behavior), you "just" share/pass the reference to this map (but watch out for concurrency, "usual" Map implementations are not thread safe):

 //not: Map<X, Y> copy = original.clone(), but:
 Map<X, Y> ref = original; // then all changes on "original" are "reflected" at "ref" ..

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Under "deep copy", I'd understand, that "keys and values" (and even deeper) get cloned, too.