Validate for Another user not to use

public void  validatewrite(Args _args)
{
     boolean ret;
    NumberSequenceTable numberSequenceTable;
     LedgerJournalName  ledger;
    ledgerjournalname  tchk;
    LedgerJournalNameId  ledgerJournalNameId;
    select tchk where tchk.CheckBox== NoYes::Yes;
        if(tchk && tchk.JournalName!= ledger.JournalName)
        {
             ledger.CheckBox= NoYes::No;
             select tchk where tchk.CheckBox== NoYes::Yes;
            ret = checkFailed("Already Journal Name: %1 is Checked",tchk.JournalName) );
            // ret = checkFailed(strFmt("selected user",tchk.JournalName));
           // throw error ("already selected by one user");

}}