Chapter 11 Exercise 14, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

11.14 (Combine two lists)
Write a method that returns the union of two array lists of integers using the following header:
public static ArrayList<Integer> union( ArrayList<Integer> list1, ArrayList<Integer> list2)
For example, the union of two array lists {2,3,1,5} and {3,4,6} is {2, 3, 1, 5, 3, 4, 6}.
Write a test program that prompts the user to enter two lists, each with five integers,
and displays their union. The numbers are separated by exactly one space in the output.

import java.util.ArrayList;
import java.util.Scanner;

public class Exercise_14 {

    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);
        ArrayList<Integer> list1 = new ArrayList<>();
        ArrayList<Integer> list2 = new ArrayList<>();
        System.out.print("Enter five integers for list1: ");
        for (int i = 0; i < 5; i++) list1.add(input.nextInt());
        System.out.print("Enter five integers for list2: ");
        for (int i = 0; i < 5; i++) list2.add(input.nextInt());

        System.out.println("The combined list is " + union(list1, list2));

    }

    public static ArrayList<Integer> union(ArrayList<Integer> list1, ArrayList<Integer> list2) {

        ArrayList<Integer> temp = new ArrayList<>();
        temp.addAll(list1);
        temp.addAll(list2);
        return temp;
    }
}