HashMap returning no Values

Question

While doing my assignment i ran into a rather strange error and can't find why my HashMap gets emptied every time.

Im in no way asking for a solution for the named assignment i just need help with this HashMap.

So what i am trying to do is to read a RSS Feed with the SAX API and save every match into a HashMap called 'results'. The second hashmap is for storing the current item i am reading.

public class SAX extends DefaultHandler{
    HashMap<Integer, HashMap<Integer,String>> results = new HashMap<Integer, HashMap<Integer, String>>();
    HashMap<Integer, String> current_item = new HashMap<Integer,String>();
    int flag = 0;
    String[] filter = {"Corona"};
    String current = "";
    int cnt_results, cnt_item = 0;
    public static void main(String[]args) throws ParserConfigurationException, SAXException, IOException {
        Init of the Sax Stuff here. This is normal stuff.
        But i use the SAX Class as a Handler.
    }
    
    public void startDocument() {
        System.out.println("Started the RSS Feed...");
    }
    
    public void endDocument() {
        for(int i = 0; i<this.results.size();++i) {
            Map<Integer,String> map = this.results.get(i);
            for(int i2 = 0; i2<map.size();++i2) {
                System.out.println(map.get(i2));
            }
        }
        System.out.println("Seems like we hit the end.");
    }
    
    public void startElement(String uri,String localName, String qName, Attributes attributes) throws SAXException {
        if(localName == "item") {
            flag = 1;
        }
    }
    
    public void endElement(String uri, String localName, String qName) throws SAXException {
        current_item.put(cnt_item, current);
        cnt_item++;
        
        // Filters if description contains one of the Keywords
        if(localName == "description") {
            for(int i = 0; i<filter.length;++i) {
                if(current.contains(filter[i])) {
                    flag = 2;
                    break;
                }
            }
        }
        
        if(localName == "item") {
            if(flag == 2) {
                if(this.results.containsValue(current_item)) {
                ;
                }else {
                this.results.put(cnt_results, current_item);
                cnt_results++;
                }
            }
            flag = 0;
            cnt_item = 0;
            current_item.clear();
        }
    }
    
    public void ignorableWhitespace(char[] ch, int start, int length) throws SAXException {
        
    }
    
    public void characters(char[] ch, int start, int length) throws SAXException{
        current = new String(ch,start,length);
    }
    
}

The Reader should then go over the RSS Feed and find every Item that has a description containing the filter word and save them into the results Map.

When trying to read these saved results i just get blank lines.

Maybe that's not the best way to express what it means so i just gave you the whole code.

Glad for your help. Thanks!

score 0 · Accepted Answer · answered Jan 05 '21 at 14:58

localName == "item"

localName == "description"

This compares reference identity. As in, "item" == "item" is false. You want "item".equals(localName) which compares the string content.

current_item.clear();

Java is reference based. current_item isn't the hashmap. It's a reference to the map. Your results hashmap also stores references, not maps. It's like treasure maps: everything is a map to the treasure, not treasure. . is: Follow the map, and dig down. so, current_item.clear() follows the map,digs down, and destroys the contents of the treasure you find. Your results hashmap has its own copy of a treasure map, but it leads to the same treasure, so you probably don't want this. Try current_item = new HashMap<>();. Instead of following the map and destroying the treasure, this creates a new treasure, buries it in the sand, and updates your map (And not any copies of this map, they remain what they were) to point at the newly buried treasure.

Oh boy/girl im glad for your help. Send straight down from heaven to save my assignment. Sometimes its the little things you miss :). Thank you. — , Jan 05 '21 at 15:06

HashMap returning no Values

1 Answers1