Java: Check variable type

Question

I'm working on an assignment where I have to sort integers and string type variables.

So I have a method declared as

public void quickSort(ArrayList<Entry<Integer, String>> list) {

but if I want to overload the method and use

public void quickSort(ArrayList<Entry<String, Integer>> list) {

It is recognized as a duplicate.

Is there a way to check what my variable types are? Alternatively, is there a way to sort strings and integers the same way so that I can do something like

public void quickSort(ArrayList<Entry<K, V>> list) {

that will work on both date types?

Andy Turner · Accepted Answer · 2018-04-13 21:40:06Z

2

You probably need to provide an explicit comparator, since there is no natural ordering of Entrys:

public <T> void quickSort(ArrayList<T> list, Comparator<? super T> comparator)

and then use that comparator inside the method for your comparisons.

The fact that you are trying to sort something with two type parameters (Map.Entry<String, Integer> or Map.Entry<Integer, String>) is not relevant from a generics perspective: it's just a single type, hence you can replace the whole thing with T.

answered Apr 13, 2018 at 21:40

Andy Turner

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Jan-Peter Schmidt · Accepted Answer · 2018-04-13 22:20:37Z

1

What also may be helpful for you is that you can check the datatype of a variable with instanceof keyword. E.g.

if (variable instanceof String) { //do stuff }

answered Apr 13, 2018 at 22:20

Jan-Peter Schmidt

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