You can combine two maps in Java by using the putAll() method of java.util.Map interface. This method copies all the mappings from one Map to another, like, if you call it like first.putAll(second), then all mappings from the second Map will be copied into the first Map. This means if the first map contains 5 elements and the second map contains 10 elements or mapping, then the combined map will contain 15 or fewer mappings. In the case of duplicate keys, the value is overridden or updated from the second map.
