How do I show two object are adjacent to each other?

Question

I have to read in a file that shows one letter (City) is adjacent to the other. They are separated by a tab.

How do I show that Q is adjacent to X, R is adjacent to X (also), P is adjacent to R, etc etc...?

Q   X
R   X
P   R
P   W
W   S
S   T
T   W
W   Y
Y   R
Y   Z

Segment of code to read in the file:

private ArrayList<City> cityList;
private ArrayList<City> cityFromList;
private ArrayList<City> cityToList;
Scanner theFlightFile = null;

    try {
        theFlightFile = new Scanner (new File("flightFile.txt"));
    }
    catch (Exception FileNotFoundException) {
        System.out.println(FileNotFoundException.getMessage());
    }
    while (theFlightFile.hasNext()) {
        String cityFrom = theFlightFile.next();
        String cityTo = theFlightFile.next();
        City cityA = new City(cityFrom);
        City cityB = new City(cityTo);

        cityToList.add(cityA);
        cityFromList.add(cityB);
        //testing input reading...
        System.out.println(cityFrom + " -----> " + cityTo);
    }

Method to that displays the names of all the cities which are adjacent to 'aCity'. @param aCity The city for which the adjacency list is desired.

    //this is completely wrong, I know...
public void displayAdjacentCities(City aCity) {
    //for (aCity  : cityFromList) {
    //  for (City cityB : cityToList) {
    //      System.out.println(cityA + " is adjacent to " + cityB);
    //  }
    //}

}

Answer 1

您可以使用HashMap<City, HashSet<City>>结构，其中键是城市对象，并且指向其相邻城市的集合。

Answer 2

The easiest way would be:

for (i = 0; i < cityFromList.length(); i++) {
  if (cityFromList.get(i).equals(aCity)) {
    System.out.println(aCity + " is adjacent to " + cityToList.get(i) + ".");
  }
}

This of course requires that the "City" class would need to implement the equals method and hence the hashcode method as well.