Map<String, String> fieldAttributes = new HashMap<String, String>();
fieldAttributes.put("a", "48");
fieldAttributes.put("b", "");
fieldAttributes.put("c", "4224");
Now I need to cast Map<String, String> to Map<Object, Object>
How can I do this. I tried ? extends Object but not sure how to use it.
You can use
Map<Object, Object> properties = (Map) fieldAttributes;
The compiler gives you an appropriate warning, but it compiles.
You can't. A Map<String, String> is not a Map<Object, Object>. If it was, you could do
Map<String, String> map = new HashMap<String, String>();
Map<Object, Object> map2 = (Map<Object, Object>) map;
map2.put(Integer.valueOf(2), new Object());
which would break the type safety that generics bring.
So, you'll indeed have to use a raw map, or use a Map<? extends Object, ? extends Object>.
Map<? extends Object, ? extends Object> genMap = fieldAttributes;
OR
Map<Object, Object> gMap = (Map)fieldAttributes;
Map<?,?>. The "extends Object" is kind of implied.
Instead of casting, you can just use Object instead of String:
Map<Object, Object> fieldAttributes = new HashMap<Object, Object>();
fieldAttributes.put("a", "48");
fieldAttributes.put("b", "");
fieldAttributes.put("c", "4224");
When iterating the Map, you can use Object's .toString() method to transform.
Map<Object,Object>is neither a subtype nor a supertype ofMap<String,String>. TryMap<?,?>instead - it's a supertype of bothMap<String,String>andMap<Object,Object>, so it might be what you want. Is the function that requiresMap<Object,Object>something you can change?