How to directly initialize a HashMap (in a literal way)?

Question

Is there some way of initializing a Java HashMap like this?:

Map test = 
    new HashMap{\"test\":\"test\",\"test\         


        

Answer 1

There is no direct way to do this - Java has no Map literals (yet - I think they were proposed for Java 8).

Some people like this:

Map test = new HashMap(){{
       put("test","test"); put("test","test");}};

This creates an anonymous subclass of HashMap, whose instance initializer puts these values. (By the way, a map can't contain twice the same value, your second put will overwrite the first one. I'll use different values for the next examples.)

The normal way would be this (for a local variable):

Map test = new HashMap();
test.put("test","test");
test.put("test1","test2");

If your test map is an instance variable, put the initialization in a constructor or instance initializer:

Map test = new HashMap();
{
    test.put("test","test");
    test.put("test1","test2");
}

If your test map is a class variable, put the initialization in a static initializer:

static Map test = new HashMap();
static {
    test.put("test","test");
    test.put("test1","test2");
}

If you want your map to never change, you should after the initialization wrap your map by Collections.unmodifiableMap(...). You can do this in a static initializer too:

static Map test;
{
    Map temp = new HashMap();
    temp.put("test","test");
    temp.put("test1","test2");
    test = Collections.unmodifiableMap(temp);
}

(I'm not sure if you can now make test final ... try it out and report here.)