Here is the updated code that seems to work, you need to type the map of maps as <String, Object>
since mp isn’t a string you can’t do <Object, String>
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import java.util.HashMap; import java.util.Iterator; import java.util.Map; import java.util.Set; import java.util.ArrayList; public class MapExample { public static void main(String[] args) { Map<Object,String> mp=new HashMap<Object, String>(); // adding or set elements in Map by put method key and value pair mp.put(new Integer(2), "Two"); mp.put(new Integer(1), "One"); mp.put(new Integer(3), "Three"); mp.put(new Integer(4), "Four"); Map<Object,String> mp2=new HashMap<Object, String>(); mp2.put(new Integer(2), "Two2"); mp2.put(new Integer(1), "One2"); mp2.put(new Integer(3), "Three2"); mp2.put(new Integer(4), "Four2"); Map<String, Object> mpMaps=new HashMap<String, Object>(); mpMaps.put("Map1",mp); mpMaps.put("Map2",mp2); System.out.println("This is a map of Maps: " + mpMaps); for (int i=0;i<mpMaps.size();i++){ ArrayList<Object> a = new ArrayList<Object>(mpMaps.keySet()); Object o=a.get(i); System.out.println("all together: "