CODEWITHSUNDEEP
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mynameisJEFF
mynameisJEFF

Reputation: 4239

Java: How can I make a clone of a HashMap of ArrayList ?

In my problem, I created an object HashMapOfArrayList. It has an instance method named transformation, which essentially remove and add edges.

Problem lies in my Testing Class. I want to create a clone of the original Object (i.e. the graph I have when I load the text file) at each iteration. I do not know how to do this. And I think reading in the file again in each iteration, which is what I have now, is really inefficient. How should I create a clone in this situation ? 

class HashMapOfArrayList{
     HashMap<Integer, ArrayList<Integer>> my_graph;

     // constructor
     public HashMapOfArrayList(){
                my_graph = new HashMap<Integer, ArrayList<Integer>>();
     }
      .......
}

class Testing{
    public static void main(String[] args) throws IOException{
        HashMapOfArrayList graph = new HashMapOfArrayList();
        graph.read_file_and_populate("file.txt");
        for(int i = 0; i < 1000; i++){ 
// Need a way to clone the object instead of reading in the file many times.
                HashMapOfArrayList graph = new HashMapOfArrayList();
                graph.read_file_and_populate("file.txt");
                graph.transformation();
                }
            }
        }
    }

Upvotes: 0

Views: 539

Answers (1)

Compass
Compass

Reputation: 5937

You need a new constructor that takes your HashMapOfArrayList as an argument, and then all you need to do is clone the Integers in the ArrayList.

public HashMapOfArrayList(HashMapOfArrayList source) {
    HashMap<Integer, ArrayList<Integer>> graph = source.getGraph(); // get the source graph

    my_graph = new HashMap<Integer, ArrayList<Integer>>(); //define our graph 
    for(Map.Entry<Integer, ArrayList<Integer>> entry : graph.entrySet()) {
        //iterate through the graph
        ArrayList<Integer> sourceList = entry.getValue();
        ArrayList<Integer> clonedList = new ArrayList<Integer>();
        clonedList.addAll(sourceList);
        //put value into new graph
        my_graph.put(entry.getKey(), clonedList);
    }
}

Then, you can replace your original read with the cloning constructor and transform it.

for(int i = 0; i < 1000; i++){ 
    HashMapOfArrayList clone = new HashMapOfArrayList(graph);
    clone.transformation();
}

Upvotes: 1

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