java Map- code issue

[yam vek]

Map code issue:

Have Map accepting values from 2 tables (txn, txn_pending)

map accepts key as txnid and value as TransactionDataModel as below,

Map<Long, Transaction> transactions = new HashMap<Long, Transaction>()
transactions.put(tpAccountTxnId, transaction);

Flow 1: queries value from table(txn) and has 3 record which occupies position : 1,11,12 in map
records keys:
tpAccountTxnId : 21804
tpAccountTxnId : 22723
tpAccountTxnId : 23604

Flow 2: TxnId which is key has null value(designed as per req) for table 2(Txn_pending) and hence have replced null values with increment values of int i=1;
records keys:
tpAccountTxnId : null
tpAccountTxnId : null

issue: when i try to replace null values with increment value of int i=1, it replaces record key 21804 which is placed in position 1 of "txn" table.

can anyone please suggest some solution to accept both txnid with null and not null values in same map without losing any record or replacing existing record.

[bhanu chowdary]

HashMap will allow only one null as a key. I didnt get your question, sorry

[Jesper de Jong]

yam vek wrote:... and has 3 record which occupies position : 1,11,12 in map ...

issue: when i try to replace null values with increment value of int i=1, it replaces record key 21804 which is placed in position 1 of "txn" table.

There's one thing I don't understand here: what do you mean with the 'position' in a map?

A Map is an unordered collection. Entries (key-value pairs) in a map do not have a position.