Converting Map to Map | 易学教程

问题

I have Two Maps

Map<String, String> filterMap 
Map<String, Object> filterMapObj

What I need is I would like to convert that Map<String, String> to Map<String, Object>. Here I am using the code

        if (filterMap != null) {
            for (Entry<String, String> entry : filterMap.entrySet()) {
                String key = entry.getKey();
                String value = entry.getValue();
                Object objectVal = (Object)value;
                filterMapObj.put(key, objectVal);
            }
        }

It works fine, Is there any other ways by which I can do this without iterating through all the entries in the Map.

回答1:

You can just use putAll:

filterMapObj.putAll(filterMap);

(See the Javadoc.)

Edited to add: I should note that the above method is more-or-less equivalent to iterating over the map's elements: it will make your code cleaner, but if your reason for not wanting to iterate over the elements is actually a performance concern (e.g., if your map is enormous), then it's not likely to help you. Another possibility is to write:

filterMapObj = Collections.<String, Object>unmodifiableMap(filterMap);

which creates an unmodifiable "view" of filterMap. That's more restrictive, of course, in that it won't let you modify filterMapObj and filterMap independently. (filterMapObj can't be modified, and any modifications to filterMap will affect filterMapObj as well.)

回答2:

You can use the wildcard operator for this. Define filterMapObj as Map<String, ? extends Object> filterMapObj and you can directly assign the filterMap to it. You can learn about generics wildcard operator