A Java Example Shown to GuaiSun

MainClass.java

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

/**
 * Created by helloqiu on 16/3/17.
 */
public class MainClass {
    public static void main(String[] args) {
        String[] order = {"first","second","third"};
        Scanner scanner = new Scanner(System.in);
        ArrayList<String> cityArray = new ArrayList<>();
        for (int i = 0 ; i < 3 ; i ++) {
            System.out.print("Enter the " + order[i] + " city: ");
            cityArray.add(scanner.nextLine());
        }
        Collections.sort(cityArray,new SortCityComparator());
        System.out.print("The three cities in alphabetical order are");
        for (String string : cityArray) {
            System.out.print(" " + string);
        }
    }
}

SortCityComparator.java

import java.util.Comparator;

/**
 * Created by helloqiu on 16/3/17.
 */
public class SortCityComparator implements Comparator {
    public SortCityComparator() {
        super();
    }
    public int compare(Object x, Object y) {
        if (((String)x).charAt(0) < (((String)y).charAt(0))) {
            return -1;
        }else {
            return 1;
        }
    }
}