java best data structure for two to many relations

Question

So I have three important factors, filenames which there are many, there will also be duplicates, violation types which there are 6 of, and the data relating to them.

I was thinking of using a Map for this but it only accepts two types, so I want to sort the data by the filename and for every entry under that filename, i want to retrieve the violation type, from what i want it to retrieve all the matches from the data, so say it's a map I could of said map.get(filename, violation) and it will retrieve all the results that match that.

Is there a data structure that can allow me to do this? or am I being lazy and should just sort the data myself when it comes to outputting it.

Answer 1

One other way to approach this would be to use a custom Class for holding the needed data. Essentially 'building' your own node that you can iterate over.

For example! you could create the following class object: (Node.java)

import java.util.*;

public class Node
{
    private String violationType;
    private String dataInside;

    public Node()
    {   
        this("", "");
    }
    public Node(String violationType)
    {
        this(violationType, "");
    }
    public Node(String violationType, String dataInside)
    {
        this.violationType = violationType;
        this.dataInside = dataInside;
    }
    public void setViolationType(String violationType)
    {
        this.violationType = violationType;
    }
    public void setDataInside(String dataInside)
    {
        this.dataInside = dataInside;
    }
    public String getViolationType()
    {
        return violationType;
    }
    public String getDataInside()
    {
        return dataInside;
    }
}

ok, great, so we have this 'node' thing with some setters, some getters, and some constructors for ease of use. Cool. Now lets see how to use it:

import java.util.*;

public class main{
    public static void main(String[] args){
        Map<String, Node> customMap = new HashMap<String, Node>();
        customMap.put("MyFilename", new Node("Violation 1", "Some Data"));
        System.out.println("This is a test of the custom Node: " + customMap.get("MyFilename").getViolationType());
    }
}

Now we have a map that relates all of the data you need it to. Now, you'll get a lot of people saying 'Don't reinvent the wheel" when it comes to things like this, because built in libraries are far more optimized. That is true! If you can find a data structure that is built into java that suits your needs, USE IT. That's always a good policy to follow. That being said, if you have a pretty custom situation, sometimes it calls for a custom approach. Don't be afraid to make your own objects like this, it's easy to do in Java, and it could save you a lot of time and headache!

EDIT

So, after re-reading the OP's question, I realize you want an entire list of associated data for the given violation of a given filename. In which case, you would switch the private String dataInside to something like private ArrayList<String> dataInside; which would allow you to associate as much data as you wanted, still inside that node, just inside of an arraylist. Also note, you'd have to switch up the getters/setters a little to accomodate a list, but that's not too bad.

Answer 2

You could use a custom class for a mapkey which contains the two fields filename and violation type. When doing so you need to implement equals() and hashCode() methods do ensure instances of that class can be used as key for map.

Answer 3

You can use TreeMap. TreeMap is sorted according to the natural ordering of its keys.

 TreeMap<String, List<String>> map = new TreeMap<String, List<String>>();