How to preserve insertion order in HashMap?

Question

I'm using a HashMap. When I iterate over the map, the data is returned in (often the same) random order. But the data was inserted in a specific order, and I need to preserve the insertion order. How can I do this?

Answer 1

Use LinkedHashMap.

It is precisely like HashMap, except that if you iterate over it, it presents the items in the injection order.

Example: 

void foo(Map m) {

         Map copy = new LinkedHashMap(m);

         ...

     }