Problems with creating a map of <String, List>

Question

I've a row in db returned by query below. Columns to select include rec, head, amount. I want to sort the rows by head column. I tried Map where string for head and list for other two columns.

I've hit the wall with my non-working code posted below. How would I append another list to list of repeated key. Documentation says it replaces the value for same key whereas I need it appended to the list value. I would be really greatful for any help.

Query q= session.createQuery("select tally_receipt_prefix, tally_receipt_no, tally_head, tally_amount from Tally_table where tally_system_date='"+fmtd_date+"' and tally_dbcr_indicator='DB' and tally_mode='Ca' order by tally_head,tally_receipt_prefix,tally_receipt_no"); System.out.println("query "+q);

List heads=new ArrayList();

for(Iterator it=q.iterate(); it.hasNext(); )
{
    Object[] row= (Object[]) it.next();

    payincash1=new LinkedHashMap<String, List>();

    heads.add((String)row[2]);

    List tails = null;
    tails=new ArrayList();
    tails.add((String)row[0]);
    tails.add((String)row[1]);
    tails.add((String)row[3]);

    System.out.println("heads in dao from iter 1: "+heads);  
    System.out.println("tails in dao from iter1 on: "+tails);

    if(heads.contains((String)row[2]))  // for head in temp list
    {
        System.out.println("in first if");
        if(payincash1.containsKey((String)row[2]))     
        {
            System.out.println("map if repeat: "+payincash1);
            payincash1.put((String)row[2],tails);
        }

    } 
    else
    {

        System.out.println("map if not repeat: "+payincash1);
        payincash1.put((String)row[2], tails);

    }

}

Can you please ask the question in a simpler way, such as "what is a sorted container which can have duplicates and has O(logN) search". BTW, is that the question? — Drakosha
– Drakosha, Commented Aug 29, 2012 at 2:40
Sorry if my question was not clear. I want to add a key (string in this case) from heads list and value (in this case a list) from tails list in my code. For each repeated head I want the value (here list) to be appended to old value ( old list ) and my efforts doing this were futile. — yoda
– yoda, Commented Aug 29, 2012 at 2:46

MadProgrammer · Accepted Answer · 2012-08-29 02:57:43Z

Sounds more like you want a list of lists

Something like Map<String, List<List>>

Then you'd end up with something like...

Map<String, List<List>> payincash1 = new LinkedHashMap<String, List<List>>();

heads.add((String) row[2]);

List tails = null;
tails = new ArrayList();
tails.add((String) row[0]);
tails.add((String) row[1]);
tails.add((String) row[3]);

System.out.println("heads in dao from iter 1: " + heads);
System.out.println("tails in dao from iter1 on: " + tails);

List master = payincash1.get((String)row[2]);
if (master == null) {

    master = new List();
    payincash1.put((String)row[2], master);

}

master.add(tails);

Now, personally, I'd be creating a "data" object that would contain all this information.

public class MyData {
    private String rec, head, amount, ??; // Apparently you have another variable I don't know about
    public MyData(String rec, String head, String amount, String ??) {
        // Initalise...
    }
    // Setters and getters not inclueded
}

Then you could do something like this...

Map<String, List<MyData>> payincash1 = new LinkedHashMap<String, List<MyData>>();

MyData data = new MyData(row[0], row[1], row[2], row[3]);

List master = payincash1.get((String)row[2]);
if (master == null) {

    master = new List<MyData>();
    payincash1.put((String)row[2], master);

}

master.add(data);

Which is a little cleaner (IMHO)

Balaji Paulrajan · Accepted Answer · 2012-08-29 03:02:56Z

4

From what I understand you need Multimap of guava library.

answered Aug 29, 2012 at 3:02

Balaji Paulrajan

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