Best way to create an empty map in java

Question

I need to create an empty map if the map its null.

if (fileParameters == null)
    fileParameters = (HashMap<String, String>) Collections.EMPTY_MAP;

The problem is that I get a code warning: Type safety: Unchecked cast from Map to HashMap what its the best way to create this emptyMap.

Answer 1

If you need an instance of HashMap, the best way is:

fileParameters = new HashMap<String,String>();

Since Map is an interface, you need to pick some class that instantiates it if you want to create an empty instance. HashMap seems as good as any other - so just use that.

Answer 2

The emptyMap method of the Collections class.

Answer 3

Collections.emptyMap()

Answer 4

Either Collections.emptyMap(), or if type inference doesn't work in your case,
Collections.<String, String>emptyMap()

Answer 5

If the Map can be immutable:

Collections.emptyMap();

// or, in some cases:
Collections.<String,String>emptyMap();

You'll have to use the latter sometimes when the compiler cannot automatically figure out what kind of Map is needed. For example, consider a method declared like this:

public void doStuff(Map<String,String> map){ ... }

When passing the empty Map directly to it, you have to be explicit about the type:

doStuff(Collections.emptyMap());                // doesn't compile
doStuff(Collections.<String,String>emptyMap()); // works fine

If you need to be able to modify the Map, then for example:

new HashMap<String,String>();

(as tehblanx pointed out)

Answer 6

What about :

Map<String, String> s = Collections.emptyMap();