CODEWITHSUNDEEP
javaarraylisthashmap
Keith
Keith

Reputation: 635

Multi Layered Hashmap and Arraylist

I was working on a java program that takes a string and splits it into different levels.

Map<String, ArrayList<Map<String, ArrayList<Map<String,Map<String, String>>>>>> courseInfoMap = new HashMap<String, ArrayList<Map<String,ArrayList<Map<String,Map<String, String>>>>>>();
ArrayList<Map<String, ArrayList<Map<String,Map<String, String>>>>> courseNumList = new ArrayList<Map<String, ArrayList<Map<String,Map<String, String>>>>>();
Map<String, ArrayList<Map<String,Map<String, String>>>> courseNumTextbookMap = new HashMap<String, ArrayList<Map<String,Map<String, String>>>>();
ArrayList<Map<String,Map<String, String>>> listOfTextbooks = new ArrayList<Map<String,Map<String,String>>>();

Map<String, Map<String, String>> textbookMap = new HashMap<String, Map<String, String>>();
Map<String, String> isbnMap = new HashMap<String,String>();

Essentially, I'm trying to have a course code --> list of course num --> course num (key) --> list of textbooks --> textbook --> isbn number(str) --> price

So because some course codes have multiple course numbers it points to an arraylist.

I have been adding stuff backwards, so loops within loops. Assuming I did not screw up there. I've been trying to loop through the elements in the same sort of way assuming they were probably added. 

for(Map.Entry<String, ArrayList<Map<String, ArrayList<Map<String,Map<String, String>>>>>> entry : courseInfoMap.entrySet()){
        System.out.println(entry.getKey());// COURSE CODE

        for(int i = 0; i < entry.getValue().size();i++){//loops through arraylist of course numbers
            System.out.println("i("+i+" - " + entry.getValue().get(i));

            for(Map.Entry<String, ArrayList<Map<String,Map<String,String>>>> entry2 : entry.getValue().get(i).entrySet()){
                System.out.println("   " + entry2.getKey());
                // . . . and so on

This hasnt worked it just loops through everything. On each level.

My question is how do I navigate through a large number of hashmaps and/or is there a better way to do this.

Example:

AAAA
     100
        Name
        ###
        $$$

        Name
        ###     <-- different from past
        $$$
     200 
        Name
        ###
        $$$
  BBBB
      101
        Name
        ###
        $$$

Upvotes: 3

Views: 1229

Answers (1)

Todd
Todd

Reputation: 31710

This seems exceedingly complicated, and frankly if I had to maintain that I'd really not look forward to it. Off the top of my head there are several other approaches you could probably take...

Use a relational database

Either an in-memory database or something like mysql or postgresql. They are designed for this sort of thing - organizing data and allowing for ad-hoc queries.

Put your data in Objects

Instead of Maps and Lists, just create an object that defines most of it in one place. Store that object in the List or Map and search for what you need directly. If you don't have too much data, a brute-force uninindexed search probably won't be that bad in wall-clock time.

Upvotes: 3

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