Preventing Memory Leak when using HashMap

Hi all,

Two classes below pass HashMap to each other, I want to avoid the
memory leak, other than using HashMap.remove(key), how to avoid memory
leak in my code below ?

FormInv class get return value from a lookup on class CashLookUp,
these are simplified code.

Thank you for your help,
Krist

public class FormInv extends PageController {
    private HashMap CashInTable;
    public void CashIn_returnAction(ReturnEvent returnEvent) {
        String vCode = null ;
        String vNo = null ;

        if (returnEvent.getReturnValue()!=null){
            this.CashInTable =(HashMap)returnEvent.getReturnValue();
            vCode = (String)this.CashInTable.get("vDocCode");
            vNo = (String)this.CashInTable.get("vDocNo");

        // Is this the only way to avoid memory leak with this HashMap ?
        // CashInTable.remove("vDocCode");
        // CashInTable.remove("vDocNo");
        }
    }
}

public class CashLookUp {
    private HashMap CashInTable;
    public String selectButton_action() {
        JUCtrlValueBindingRef
tabelCheck=(JUCtrlValueBindingRef)this.getCashInLov_Table().getRowData();
        String docCode =
(String)tabelCheck.getRow().getAttribute("DocCode");
        String docNo =
(String)tabelCheck.getRow().getAttribute("DocNo");
        CashInTable= new HashMap();
        CashInTable.put("vDocCode",docCode);
 
CashInTable.put("vDocNo",docNo);
 
AdfFacesContext.getCurrentInstance().returnFromDialog(CashInTable,null);
        return null;
    }
}