Java Generics - Define Method only accepts List or Maps

Question

I have defined a method in Java like below

public void processData(Object input) {
if(!(input instanceof List || input instanceof Map)) {
      throw new RuntimeException("Invalid argument type. method accept only Map type or List type");
    }

if(input instanceof List) {
//Do something
} else if(input instanceof Map) {
//Do Something
}
}

The above method just works fine. But is there a way to use generics here to show compile time error if user tries calls the method with unexpected argument? Method that only accepts List or Map ? <T extends Collection> wont work because Map is not part of Collection. Is there any other way ?

You should not write your method this way. It seems to do very different things depending on whether the parameter is a List vs a Map. You should write two methods instead. — Sweeper
– Sweeper, Commented Jul 6, 2020 at 6:43
As Java allows two methods to have the same name but different parameter types, there is no reason not to write two methods, as @Sweeper suggests. — tgdavies
– tgdavies, Commented Jul 6, 2020 at 6:58
As @Sweeper and @tgdavies mentioned, you can use a mechanic called 'method overloading'. This basically means you can create one method with a List as parameter, and one with a Map as parameter. Both can have the same name. (With a link if you want to read more about method overloading) — n247s
– n247s, Commented Jul 6, 2020 at 7:06
How to define a method in interface ? Can we have two methods with same name in Interface ? — user2731629
– user2731629, Commented Jul 6, 2020 at 9:30

Marc · Accepted Answer · 2020-07-06 10:05:59Z

3

The answer is no. The only common super class between Map and List is Object. As others mentioned in the comments, you could simply create two methods, one that accepts a List and another that accepts a Map:

public void processData(List input) {
    // Do something
}

public void processData(Map input) {
    // Do Something
}

edited Jul 6, 2020 at 10:05

answered Jul 6, 2020 at 7:52

Marc

3,3952 gold badges19 silver badges24 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

user2731629 Over a year ago

How to define a method in interface ? Can we have two methods with same name in Interface ? And also user needs to override two methods and one leaves empty

Marc Over a year ago

@user2731629 please consider accepting the answer if you are satisfied ;)

Collectives™ on Stack Overflow

Java Generics - Define Method only accepts List or Maps

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related