Java alphabetizing three cities using if else statements and compareTo

Question

Hi I'm super lost as to how you would compare three things. The textbook example is:

Scanner input = new Scanner(System.in);

System.out.print("Enter the first city: ");
String city1 = input.nextLine();
System.out.print("Enter the second city: ");
String city2 = input.nextLine();
System.out.print("Enter the third city: ");
String city3 = input.nextLine();

if (city1.compareTo(city2) < 0)
  System.out.println("The cities in alphabetical order are:");
  System.out.println(city1);
  System.out.println(city2);

else
  System.out.println("The cities in alphabetical order are:");
  System.out.println(city2);
  System.out.println(city1);

So how would you compare a third and alphabetize?

Answer 1

You can sort alphabetical, the term is lexicographical, by using built in sorting algorithms (or your own). For example by using Collections#sort (documentation). Note that Strings are comparable and use the lexicographical order by default. That is why you do not need to explicitly specify the order, for example by using a Comparator object.

This snippet sorts the cities and prints them:

List<String> cities = Arrays.asList({city1, city2, city3});
Collections.sort(cities);

System.out.println("Cities sorted lexicographical:");
for (String city : cities) {
    System.out.println(city);
}

Or if you prefer a compact Java 8 solution using Streams (it essentially falls back to the same methods, especially the same sorting method):

Stream.of(city1, city2, city3).sorted().forEach(System.out::println);

---

Note that the String#compareTo method also compares for lexicographical order, as said before. So instead of using a sorting algorithm (which checks the results of compareTo in a clever way) you can also directly hardcode the comparisons (like you already tried):

String smallestCity;
if (city1.compareTo(city2) < 0 && city1.compareTo(city3) < 0) {
    smallestCity = city1;
} else if (city2.compareTo(city1) < 0 && city2.compareTo(city3) < 0) {
    smallestCity = city2;
} else if (city3.compareTo(city1) < 0 && city3.compareTo(city2) < 0) {
    smallestCity = city3;
} else {
    throw new AssertionError("There is no strict order!");
}

String biggestCity;
if (city1.compareTo(city2) > 0 && city1.compareTo(city3) > 0) {
    biggestCity = city1;
} else if (city2.compareTo(city1) > 0 && city2.compareTo(city3) > 0) {
    biggestCity = city2;
} else if (city3.compareTo(city1) > 0 && city3.compareTo(city2) > 0) {
    biggestCity = city3;
} else {
    throw new AssertionError("There is no strict order!");
}

String middleCity;
if (city1.compareTo(smallestCity) > 0 && city1.compareTo(biggestCity) < 0) {
    middleCity = city1;
} else if (city2.compareTo(smallestCity) > 0 && city2.compareTo(biggestCity) < 0) {
    middleCity = city2;
} else if (city3.compareTo(smallestCity) > 0 && city3.compareTo(biggestCity) < 0) {
    middleCity = city3;
} else {
    throw new AssertionError("There is no strict order!");
}

The method String#compareTo returns 0 if the elements are equal, < 0 if the first element is smaller and > 0 if greater than the second element (documentation).

But as said, a sorting algorithm performs these checks in a far more clever way, with less comparisons. So you should use one.