Java: can't use Map.Entry to iterate over a Map?

April 29, 2022

Every Java Map iteration example I’ve seen recommends this paradigm:

for (Map.Entry<String, String> item : hashMap.entrySet()) {
   String key = item.getKey();
   String value = item.getValue();
}

However, when I attempt to do this I get a warning from my compiler:

Incompatible types: java.lang.Object cannot be converted to java.util.Map.Entry<java.lang.String, java.lang.Object>

Here’s my code – the only wrinkle I see is that I’m iterating over an array of Map objects, and then iterating over the elements of the individual Map:

result = getArrayOfMaps();
// Force to List LinkedHashMap
List<LinkedHashMap> result2 = new ArrayList<LinkedHashMap>();
for (Map m : result) {
  LinkedHashMap<String, Object> n = new LinkedHashMap<>();
  for (Map.Entry<String, Object> entry : m.entrySet()) {
     n.put(entry.getKey(),entry.getValue());
  }
  result2.add(n);
}

Am I missing something blatantly obvious?

>Solution :

This is happening because you are using raw types: a List<LinkedHashMap> instead of a List<LinkedHashMap<Something, SomethingElse>>. As a result, the entrySet is just a Set instead of a Set<Map.Entry<Something, SomethingElse>>. Don’t do that.