CODEWITHSUNDEEP
java
Moro
Moro

Reputation: 2128

clone utility for HashMap in java

Is there java utility that does clone() method for HashMap such that it does copy of the map elements not just the map object (as the clone() in HashMap class)?

Upvotes: 7

Views: 25028

Answers (5)

Andrew
Andrew

Reputation: 37969

Often copy should be deep. Here is an example how to "deep copy"

Map<Integer, ArrayList<Integer>>

code:

public static Map<Integer, ArrayList<Integer>> deepCopyMapIntList
        (Map<Integer, ArrayList<Integer>> original) {

    Map<Integer, ArrayList<Integer>> copy = new HashMap<>(original.size());

    for (int i : original.keySet()) {
        ArrayList<Integer> list = original.get(i);

        copy.put(i, (ArrayList<Integer>) list.clone());
    }
    return copy;
}

Upvotes: 0

Oso
Oso

Reputation: 528

Once you know your key/value pair elements are cloneable:

HashMap<Foo, Bar> map1 = populateHashmap();
HashMap<Foo, Bar> map2 = new HashMap<Foo, Bar>();

Set<Entry<Foo, Bar>> set1 = map1.entrySet();
for (Entry<Foo, Bar> e : l)
    map2.put(e.getKey().clone(), e.getValue().clone());

Upvotes: 1

Ian Durkan
Ian Durkan

Reputation: 1232

The SO question Deep clone utility recommendation is similar to this one, and has an answer that may be helpful to you.

To summarize, they recommend using the Cloning library from Google Code. From personal experience, it deep-copies HashMaps. It can even clone things that aren't Cloneable.

Upvotes: 1

Matthew Flaschen
Matthew Flaschen

Reputation: 284836

Take a look at the deepClone method at http://www.devdaily.com/java/jwarehouse/netbeans-src/db/libsrc/org/netbeans/lib/ddl/impl/SpecificationFactory.java.shtml . It is not generic, but it includes several built-in types (including HashMap itself, recursively), and can obviously be extended.

Upvotes: 0

Michael Borgwardt
Michael Borgwardt

Reputation: 346317

What about other objects referred to in the elements? How deep do you want your clone?

If your map elements don't have any deep references and/or everything is Serializable, you can serialize the map via ObjectOutputStream into a ByteArrayOutputStream and then deserialize it right away.

The only other alternative is to do it manually.

Upvotes: 12

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