转换地图<String,String>到地图<String,Object>

Question

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.

Answer 1

Instead of writing your own loop that calls put , you can putAll , which does the same thing:

filterMapObj.putAll(filterMap);

(See the Javadoc .)

And as Asanka Siriwardena points out in his/her answer, if your plan is to populate filterMapObj immediately after creating it, then you can use the constructor that does that automatically:

filterMapObj = new HashMap<>(filterMap);

But to be clear, the above are 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 (eg, 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.)

Answer 2

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

Answer 3

你可以简单地写

Map<String, Object> filterMapObj = new HashMap<>(filterMap);

Answer 4

可以使用putAll方法来解决这个问题。Object是所有对象的父类，所以不用转换就可以使用putAll。