Copying a HashMap in Java

java copy hashmap clone
user691305 picture user691305 · Apr 9, 2012 · Viewed 225.6k times · Source

I am trying to keep a temporary container of a class that contains member :

HashMap<Integer,myObject> myobjectHashMap

A class called myobjectsList

Then I do

myobjectsListA = new myobjectsList();
myobjectsListB = new myobjectsList();

then: Add some hashmap items to A (like 2)

then:

myobjectListB = myobjectListA; //B has 2

then: Add hashmap items to A (like 4 more)

then: return A to the items stored in B

myobjectListA = myobjectListb;

But when I do this, B grows with A while I am adding hashmap items to A. A now has 6 items in it because B had 6.

I want A to still have the original 2 at the end after last assignment. In C++ I would use copy with objects, what is the java equivalent?

Added: OK I left something out explaining this. MyObjectsList does not contain the HashMap, it is derived from a class MyBaseOjbectsList which has the HashMap member and MyObjectsList extends MyBaseOjbectsList. Does this make a difference?

Answer

ratchet freak picture ratchet freak · Apr 9, 2012

If you want a copy of the HashMap you need to construct a new one with.

myobjectListB = new HashMap<Integer,myObject>(myobjectListA);

This will create a (shallow) copy of the map.

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