Shorthand for loop in Java with Collections and Arrays

Issue

I have a function that takes in an array of Sets, and I want to iterate through them.

In the implementation below f1, I was able to successfully run it.

public static void f1(Set<Integer>[] sets){
    for (int i = 0; i < sets.length; i++) {
        for (int j : sets[i]) {
            System.out.println(j);
        }
    }
}

However, when I try the java shorthand for loop below in f2, it throws an error: error: incompatible types: Object cannot be converted to int for (int i : s) {

public static void f2(Set<Integer>[] sets){
    for (Set s : sets) {
        for (int i : s) {
            System.out.println(i);
        }
    }
}
    

I wasn't sure why it doesn't work, since as I am iterating through the array, while each element is a set I create a dummy variable s to refer to that set, then I create another dummy variable i for an int. The error message suggests maybe I need a cast of some sort for int, but I don't quite see where, since int i is already an integer.

Solution

When you write Set without <> for java this means you don't care about generic type of Set, this is close enough to Set<?> or Set<Object>, so, java will not even try to determine the generic type. If you wish to write the short code without <> you can use var in your case:

public static void f2(Set<Integer>[] sets){
    for (var s : sets) {
        for (int i : s) {
            System.out.println(i);
        }
    }
}

Works for java 10+

Answered By - SemperAnte