How to iterate through LinkedHashMap with lists as values

Question

I have following LinkedHashMap declaration.

LinkedHashMap<String, ArrayList<String>> test1 

my point is how can i iterate through this hash map. I want to do this following, for each key get the corresponding arraylist and print the values of the arraylist one by one against the key.

I tried this but get only returns string,

String key = iterator.next().toString();   ArrayList<String> value = (ArrayList<String> )test1.get(key) 

Answer 1

for (Map.Entry<String, ArrayList<String>> entry : test1.entrySet()) {     String key = entry.getKey();     ArrayList<String> value = entry.getValue();     // now work with key and value... } 

By the way, you should really declare your variables as the interface type instead, such as Map<String, List<String>>.

Answer 2

I'm assuming you have a typo in your get statement and that it should be test1.get(key). If so, I'm not sure why it is not returning an ArrayList unless you are not putting in the correct type in the map in the first place.

This should work:

// populate the map Map<String, List<String>> test1 = new LinkedHashMap<String, List<String>>(); test1.put("key1", new ArrayList<String>()); test1.put("key2", new ArrayList<String>());  // loop over the set using an entry set for( Map.Entry<String,List<String>> entry : test1.entrySet()){   String key = entry.getKey();   List<String>value = entry.getValue();   // ... } 

or you can use

// second alternative - loop over the keys and get the value per key for( String key : test1.keySet() ){   List<String>value = test1.get(key);   // ... } 

You should use the interface names when declaring your vars (and in your generic params) unless you have a very specific reason why you are defining using the implementation.