Java ArrayList: create a copy of array and use seperate from old, but don't create new objects

问题

For example, I have an ArrayList:

ArrayList<Animal> zoo = new ArrayList<Animal>();
// some code to add animals to zoo

I want to create a copy of this old zoo to new zoo, and I can use remove/add... to process this new zoo.(and of course, it will not affect to old zoo). So, I have a way that: create new zoo that clone each animals in old zoo (it means create animal objects). So, it too SLOW.

I have an another way: create a reference of each animals of old zoo and copy to new zoo. So, new zoo just hold reference to animals of zoo. So, each time I remove/add,... It just delete reference to animal objects. No affect old zoo, and NO CREATE a new object.

But, I don't know how to do it in Java. Please teach me.

Thanks :)

回答1:

This is very simple in Java:

ArrayList<Animal> copy = new ArrayList<Animal>(zoo);

The constructor ArrayList<T>(Collection<? extends E> c) performs a shallow copy of the list that you supply as parameter, which is precisely the semantics that you are looking for.

回答2:

Simply try :

ArrayList<Animal> newZoo = new ArrayList<Animal>(oldZoo);

来源：https://stackoverflow.com/questions/10124333/java-arraylist-create-a-copy-of-array-and-use-seperate-from-old-but-dont-crea