How to putAll on Java hashMap contents of one to another, but not replace existing keys and values?

Question

I need to copy all keys and values from one A HashMap onto another one B, but not to replace existing keys and values.

Whats the best way to do that?

I was t

Answer 1

You can make it in just 1 line if you change maps order in @erickson's solution:

mapWithNotSoImportantValues.putAll( mapWithImportantValues );

In this case you replace values in mapWithNotSoImportantValues with value from mapWithImportantValues with the same keys.