Java HashMap Did Not Return Expected Result

Question

I have one doubt regarding xml reading using Stax Parser. Expected Result:

hq_seq_mast {SEQ_VAL=SEQ_VAL, 1=column,LAST_SEQ_VAL=LAST_SEQ_VAL, 2=column} db_sequence_info{TNAME=TNAME, 3=column, CNAME=CNAME, 4=column}

Actual Result:

{hq_seq_mast={}, db_sequence_info={}}

What Mistake I have Done.

import javax.xml.stream.XMLStreamReader;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamException;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.LinkedHashMap;
public class SaxDiffChecker {
public static LinkedHashMap<String,LinkedHashMap<String,String>>FirstxmlCollection=new LinkedHashMap<String,LinkedHashMap<String,String>>();
public static LinkedHashMap<String,String> firstXml=new LinkedHashMap<String,String>();
public static String tableName=null;
public static String tableendElement=null;
public static String columendElement=null;
public static String characterElement=null;
public static String tempendElement=null;
public static String tempName=null;
public static String ntempName=null;
public static int key=0;
public void print(String fileLocation) {
 try {
 FileInputStream fileInputStream = new FileInputStream(fileLocation);
 XMLStreamReader xmlStreamReader = XMLInputFactory.newInstance().createXMLStreamReader(fileInputStream);
 while (xmlStreamReader.hasNext()) {
 printEventInfo(xmlStreamReader);
 }
 System.out.print("======="+FirstxmlCollection);
 xmlStreamReader.close();
 } catch (XMLStreamException e) {
 e.printStackTrace(); //To change body of catch statement use File | Settings | File Templates.
 } catch (FileNotFoundException e) {
 e.printStackTrace(); //To change body of catch statement use File | Settings | File Templates.
 }
}
 private static void printEventInfo(XMLStreamReader reader) throws XMLStreamException {
 int eventCode = reader.next();
 switch (eventCode) {
 case 1 :
 //System.out.println("event = START_ELEMENT");
 //System.out.println("Localname = "+reader.getLocalName()+" Attribute Name"+reader.getAttributeValue(0));
 if("table".equalsIgnoreCase(reader.getLocalName())){
 tableName=reader.getAttributeValue(null,"name");
 tableendElement=reader.getLocalName();
 }else if("column".equalsIgnoreCase(reader.getLocalName())){
 columendElement=reader.getLocalName();
 firstXml.put(reader.getAttributeValue(0),reader.getAttributeValue(0));
 }else{
 tempendElement=reader.getLocalName();
 }
 break;
 case 2 :
 //System.out.println("event = END_ELEMENT");
 //System.out.println(tableendElement+"Localname = "+reader.getLocalName());
 if(tableendElement.length()>0 && tableendElement!=null && tableendElement.equalsIgnoreCase(reader.getLocalName())){
 System.out.println(tableName+"Heeee"+firstXml);
 FirstxmlCollection.put(tableName,firstXml);
 firstXml.clear();
 }else if(columendElement.length()>0 && columendElement!=null && columendElement.equalsIgnoreCase(reader.getLocalName())){
 firstXml.put(""+key++,columendElement);
 }
 break;
 case 3 :
 //System.out.println("event = PROCESSING_INSTRUCTION");
 //System.out.println("PIData = " + reader.getPIData());
 break;
 case 4 :
 //System.out.println("event = CHARACTERS");characterElement
 //System.out.println("Characters = " + reader.getText());
 break;
 case 5 :
 //System.out.println("event = COMMENT");
 //System.out.println("Comment = " + reader.getText());
 break;
 case 6 :
 System.out.println("event = SPACE");
 System.out.println("Space = " + reader.getText());
 break;
 case 7 :
 System.out.println("event = START_DOCUMENT");
 System.out.println("Document Started.");
 break;
 case 8 :
 //System.out.println("event = END_DOCUMENT");
 System.out.println("Document Ended");
 break;
 case 9 :
 //System.out.println("event = ENTITY_REFERENCE");
 //System.out.println("Text = " + reader.getText());
 break;
 case 11 :
 //System.out.println("event = DTD");
 //System.out.println("DTD = " + reader.getText());
 break;
 case 12 :
 //System.out.println("event = CDATA");
 //System.out.println("CDATA = " + reader.getText());
 break;
 }
}
public static void main(String[] args) {
 SaxDiffChecker eventsPrinter = new SaxDiffChecker();
 eventsPrinter.print("C:\\Users\\vellikutti\\Desktop\\bala.xml");
 }

}

xml:
<data-dictionary name="hq">
 <table engine-type="InnoDB" name="hq_seq_mast" scope="HQ">
 <columns>
 <column name="SEQ_VAL">
 <data-type>int(10)</data-type> 
 <nullable>false</nullable> 
 </column>
 <column name="LAST_SEQ_VAL">
 <data-type>int(10)</data-type> 
 <nullable>false</nullable> 
 </column>
 </columns>
 </table>
 <table engine-type="InnoDB" name="db_sequence_info" scope="HQ">
 <columns>
 <column name="TNAME">
 <data-type>varchar(30)</data-type> 
 <nullable>false</nullable> 
 </column>
 <column name="CNAME">
 <data-type>varchar(30)</data-type> 
 <nullable>false</nullable> 
 </column>
 </columns>
 </table>

Answer 1

Here is your problem firstXml.clear(). The data is being cleared. You may want to make firstXml a local variable or set it to firstXml = new LinkedHashMap<String,String>();, instead of clearing it.

Code Changes:

//create new map instead of clearing saved map (remember - obj passed by ref)
firstXml=new LinkedHashMap<String,String>();//firstXml.Clear();

Result:

hq_seq_mastHeeee [SEQ_VAL:SEQ_VAL, 0:column, LAST_SEQ_VAL:LAST_SEQ_VAL, 1:column]
db_sequence_infoHeeee [TNAME:TNAME, 2:column, CNAME:CNAME, 3:column]
Document Ended
=======[hq_seq_mast:[SEQ_VAL:SEQ_VAL, 0:column, LAST_SEQ_VAL:LAST_SEQ_VAL, 1:column], db_sequence_info:[TNAME:TNAME, 2:column, CNAME:CNAME, 3:column]]

• BALASCJP: Dear user845279 now result like {hq_seq_mast={}, db_sequence_info={}}
• user845279: @BALASCJP - I just tested it, replace firstXml.clear() with firstXml = new LinkedHashMap<String,String>() and it'll work.
• BALASCJP: What is exact difference between firstXml.clear() & firstxml=new LinkedHashMap<String,String>();. In above I first assigned FirstxmlCollection.put(tableName,firstXml); and then only cleared then how the problem arises can you please explain it firstXml.clear()
• user845279: I'm not sure if I can explain the idea in a comment, you should read about pass by reference. The line FirstxmlCollection.put(tableName,firstXml); doesn't make a copy of the firstXml object, it just points to it. So when you execute firstXml.clear(), you are clearing the only existing copy of the list. In order for this to work, you have to create a new list and leave the other one as it is. Try and look up Pass-by-Reference vs Pass-by-Value, it's a big part of OOP.
• BALASCJP: Thank u very much for your explanation.One doubt I declared firstXml as static then only this problem arises right???