Literal declaration of HashMap in Java

java hashmap literals

11,911

Solution 1

Though {{ (double brace) is an anti pattern, something like this you can write

HashMap<String, String> map = new HashMap<String, String>(){{
put("Key 1", "Value 1");
put("Key 2", "Value 2");
put("Key 3", "Value 3");    
}};

Edit :

If you are looking for a better way to put elements, iterate over your json and put key values in a loop.

Solution 2

There is no concept of map literals in Java but you can easily write a utility method to achieve something similar. See this implementation for example. You can then initialise a map (using static imports):

Map<String, String> map = map("k1", "v1", "k2", "v2");

An alternative is to use the "double brace initialisation" syntax but it creates an anonymous inner class which is not necessarily a good idea.

11,911

Author by

Shahid Thaika

I am an IT professional with over 10 years of work experience

Updated on June 04, 2022

Comments

Shahid Thaika about 2 years
In JavaScript, you can declare all the keys and value combinations for a JSON object in one go as follows...
```
var myJSON = {
    'key1' : 'value 1',
    'key2' : 'value 2',
    'key3' : 'value 3',
    'key4' : 'value 4',
    'key5' : 'value 5',
    'key6' : 'value 6'
};
```
I was wondering whether we can do something similar in Java for HashMaps.
```
HashMap<String, String> map = new HashMap<String, String>(
    "Key 1", "Value 1",
    "Key 2", "Value 2",
    "Key 3", "Value 3"
);
```
Basically, I need this as a one time read only thing as Config for the other parts of my code. I searched and tried a few solutions, but was not able to make them work. Or is there a better approach that I can do?
Maroun almost 9 years

Yes.. I don't like the double "{" solution.
assylias almost 9 years

@JordiCastilla or not! The map will hold a reference to the enclosing class which may be undesirable...
Jordi Castilla almost 9 years

just missing a quote in "Value 3 .... ;)
Jordi Castilla almost 9 years

@assylias my opinion... but this is the way OP is asking, I like more your example, yes, but OP is asking for a static way similar to JSon... and this is the way...
Shahid Thaika almost 9 years

I did ask if there was a better solution at the end. I guess this is a solution, but it may be preferable to go with assylias' reply, yes? Basically, this is just a one time read only variable thing. I will not be manipulating it. So would prefer the most efficient method.
Suresh Atta almost 9 years

@ShahidThaika you can freely choose your answer :)
Shahid Thaika almost 9 years

I meant to confirm this - This reply is the solution to my question, but from a programming standpoint, it may be better to code using assylias' reply. In other words, choose this as an answer, but code using the other.
Suresh Atta almost 9 years

@ShahidThaika My answer will be different if you ask for what is the best way to add elements, My answer purely concentrated on Literal declaration of HashMap in Java :)
Shahid Thaika almost 9 years

Can you add that too, then I will close by choosing this reply.
Suresh Atta almost 9 years

@ShahidThaika That will be adding in a loop. Updating that