Help me in solving AOJ201E problem

help
,
1

My issue

what is this code used for:- for (int element : set) and how can we write direct element in sopln to print the element

My code

// Update the _ to solve
import java.util.*;

class Codechef {
    public static void main(String[] args) {
        Scanner read = new Scanner(System.in);
        int t = read.nextInt();
        for (int i = 0; i < t; i++) {
            int n = read.nextInt();
            ArrayList<Integer> a = new ArrayList<Integer>();
            for (int j = 0; j < n; j++) {
                a.add(read.nextInt());
            }
            HashSet<Integer> set = new HashSet<Integer>(a);
            for (int element : set) {
                System.out.print(element + " ");
            }
            System.out.println();
        }
    }
}

Learning course: Java for problem solving - 2
Problem Link: CodeChef: Practical coding for everyone