How to access and modify elements of an int array within a Tree Map

Question

So I'm doing a Star Trek themed project where I need to take a list of crew members and the planets they've visited and generate a log report for Starfleet.

For example this...

Guinan,Drema IV
Picard,Gamalon V
Barclay,Valo III
Riker,Theydat IV
Pulaski,Alpha Moon
Troi,Tessen III
...

Needs to become this

Acamar III:
  B. Crusher             11
  Barclay                 6
  Data                   15
  Gomez                   3
  Guinan                  4
  Lefler                  5
  O'Brien                12
  Ogawa                   4
  Picard                  5
  Pulaski                14
  Riker                  12
  Troi                    9
  W. Crusher              4
  Worf                   14
  Yar                     3
...

To do this I need to use a generic structure that automatically sorts the incoming data so I decided to use a Tree Map of 15-element int arrays to store the number of visits each crew member has made to a given planet.

My question is, since I am very new to Java, how would I get a value from an array element inside the tree map and update the value inside a given array element? My problem is that all the examples I can find about working with Tree Map either don't involve arrays inside of them or don't show how to get a value and update values after the first insertion. Below I've given my current psuedocode with my best guess as to how to accomplish this. If anyone knows of a way to do this, or a better method entirely please suggest it.

P.S. I'm going to implement the loop I need after I can get a single iteration written correctly

EDIT: For clarity, each element of the 15-element int array corresponds to a crew member so for example Data would be array[2] and Yar would be array[14]

import java.util.*;
public class TreeMapDemo {

   public static void main(String args[]) {
      // Create a hash map
      TreeMap tm = new TreeMap();
      int indexDesired;
      int visits;
      String planetNameVariable;
      String crewMemberName;

      //Scan input using Scanner and assign planet name and crew name to 
      //correct variables (code provided by instructor)

      // Put elements to the map
      //if(planet doesn't already exist in tm)
          tm.put(planetNameVariable, new int[14]);

      //Decides which element of the array must be incremented
      indexDesired = crewToIndex(crewMemberName);

      //Increments visit count of crewMemberName on planetNameVariable
      visits = //How do I get the value of the array associated with planetNameVariable at indexDesired?
      tm.put(planetNameVariable, int[indexDesired] = visits + 1 //How do I insert into an array element here?);

      // Get an iterator
      Iterator i = set.iterator();

      // Display element
      // Code not designed yet

   }
}

score 1 · Answer 1 · answered Oct 04 '16 at 03:34

You can something like this. Here you have to put array in map only once because after that you will get only reference so if you modify that it will be modified in map as well.[shallow copy]

int visits[] = null;
    // Increments visit count of crewMemberName on planetNameVariable
    visits = tm.get(planetNameVariable);
    if (visits == null) {
        tm.put(planetNameVariable, new int[14]);
        visits = tm.get(planetNameVariable);
    }
    visits[indexDesired]++;

    // Get an iterator
    Iterator<String> iterator = tm.keySet().iterator();
    while (iterator.hasNext()) {
        String key = iterator.next();
        int[] temp = tm.get(key);
        if (temp != null) {
            for (int i = 0; i < temp.length; i++) {
                System.out.println(key + " " + temp[i]);
            }
        }
    }

How to access and modify elements of an int array within a Tree Map

1 Answers1