hash map with arraylist and create new arraylist out of it

Question

I am trying to clean my code and want to used optimised approches in the code.

Currently I have hashmap of this type private HashMap<String, ArrayList<allProperty>> fData;

So The data is coming from server in every 5 second. and I am updating this hashmap every 5 second something like this

       fData.put("Student", allStudent);
       fData.put("Emp", allEmp);
       fData.put("Other", allOther);

So from allproperty class object, there is marks fields and I am trying to extract that marks field for all key and creating new arraylist of integer so that I can append the marks in created arraylist by every 5 second.

I was using different arraylist for each student, emp and other before and it was working fine but it seems like alot of repeation of code. That is why I am trying to achieve it with hash map

I am trying soemthing like this but it is not appending data ...

for (String type: allTypes) {
            if(fData.get(type).size() > 0){
                arraySort(fData.get(type));
                temp = new ArrayList<Integer>();
                temp.add(fData.get(type).get(0).marks);
            }
            cData.put(type, temp);

cType is hashMap of type given below and

 private HashMap<String, ArrayList<Integer>> cData;

where allTypes is

 signalTypes.add("Student");
    signalTypes.add("Emp");
    signalTypes.add("Other");

at the end I want three new arraylist with key and able to append data in every 5 seconds. Thanks

Are you sure it would not be better using 'addAll' for temp? It is not clear what the type of fData and marks. — Gábor Bakos
– Gábor Bakos, Commented Nov 22, 2014 at 11:09
try print this in log fData.get(type).get(0).marks does it get data correctly? it should give int.. as temp is ArrayList<Integer> — Mohammed Ali
– Mohammed Ali, Commented Nov 22, 2014 at 11:09
yes it gets but the problem is when I get new data after 5 second, it does not append in new created arraylist ..I hope I am clear — user3290805
– user3290805, Commented Nov 22, 2014 at 11:10

Ruslan Ostafiichuk · Accepted Answer · 2014-11-22 12:34:29Z

2

Get your ArrayList

2a. If it doesn't exist - put your new ArrayList

2b. Else USE this ArrayList. It's mutable. So you can call .add on this object and it will be updated in HashMap

Try this:

for (String type: allTypes) {
        if (fData.get(type).size() > 0) {
            arraySort(fData.get(type));
            if (cData.get(type) == null) {
                temp = new ArrayList<Integer>();
                temp.add(fData.get(type).get(0).marks);
                cData.put(type, temp);
            } else {
                cData.get(type).add(fData.get(type).get(0).marks);
            }
        }
}

edited Nov 22, 2014 at 12:34

answered Nov 22, 2014 at 11:21

Ruslan Ostafiichuk

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5 Comments

user3290805 Over a year ago

but I guess I am doing the same ...the idea is to update each arrraylist specific to key

Ruslan Ostafiichuk Over a year ago

You creating new ArrayList instead of using old one in your code. When you use old one you shouldn't call map.put()

user3290805 Over a year ago

but if I would not create new one, then the loop will run for three times and add three values instead one for particular key

user3290805 Over a year ago

this is the error...as there is not object exist Attempt to invoke virtual method 'boolean java.util.ArrayList.add(java.lang.Object)' on a null object reference

Ruslan Ostafiichuk Over a year ago

put == null instead of != null

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