Programmer Programmer - 1 month ago 18
Java Question

How to iterate hashmap in reverse order in Java

I am trying this for some hour but not finding any best approach to achieve iteration of hashmap in reverse order, this is the hashmap I have.

Map<Integer, List<String>> map = new HashMap<Integer, List<String>>();

for(Integer key : map.keySet()) {
List<String> value = map.get(key);
List<Map<String,?>> security = new LinkedList<Map<String,?>>();
for(int ixy = 0; ixy < value.size()-1; ixy++){
security.add(createItem(value.get(ixy), value.get(ixy+1)));
}
adapter.addSection(Integer.toString(key), new SimpleAdapter(getApplicationContext(), security, R.layout.list_complex, new String[] { ITEM_TITLE, ITEM_CAPTION }, new int[] { R.id.list_complex_title, R.id.list_complex_caption }));
}


I have seen example of TreeMap as well,

Map<Integer, List<String>> sortedMap = new TreeMap<Integer, List<String>>(map);


But treemap also gives in ascending order, what I want is in descending order.

Answer

Hashmap does not have specific order. But you can use TreeMap.

Perhaps this simple example can help you :

Map<Integer, String> map = new TreeMap<Integer, String>();
        map.put(1, "abc1");
        map.put(2, "abc2");
        map.put(3, "abc3");

        ArrayList<Integer> keys = new ArrayList<Integer>(map.keySet());
        for(int i=keys.size()-1; i>=0;i--){
            System.out.println(map.get(keys.get(i)));
        }
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