Updating a Map

Question

I have a map like this:

private Map<String, List<List<String>>> someMap;
private List<List<String>> someList1;
private List<String> someList2;

....Some initialization..... ....Some list population....

Then I have,

if(someMap.get(someKey) == null){
     someList1.add(someList2);
     someMap.put(someKey, someList1);
} else {
     someMap.get(someKey).add(someList2);
}

Note that the list gets clear after adding to the map and gets populated afterward.

For instance, I have two keys "Apple" and "Orange" with some values. After the loop, I get only Orange. The previous key gets overridden!!!

EDIT: In every iteration of a loop, a list gets populated. End of the loop, it gets added to the map and after adding, the list gets clear().

Any advice? Thanks.

CODE: http://pastebin.com/m2712e04 [On request.. so please don't blame me for posting it..]

Answer 1

I doubt that you want to add the same lists over and over again. You need to create new list instances for each new key.

Edit: Does your someKey variable change at all? Have you used the debugger to step into the code and look what is happening?

Edit: Do it more like this:

// store the current payment info
reportDataSubList = new ArrayList<String>();
reportDataSubList.add(clientCode);
//...                             
reportDataList = reportData.get(clientCode);
if(reportDataList == null){
    reportDataList = new ArrayList<List<String>>();
    reportData.put(clientCode, reportDataList);
}
reportDataList.add(reportDataSubList);

But I'm not sure that the data structure you're using is well suited for the task. Proper entity objects or even XML would be a batter match IMHO.

Answer 2

Based on your comment to Lucero's question:

Are you reusing the same List instance over and over again, i.e. doing

 someList1.add(someList2);
 someMap.put(someKey, someList1);
 someList1.clear()
 someList1.add(stuff)
 someMap.put(someOtherKey, someList1);

That will not work, as someList1.clear() will clear the list inside someMap. You need to create a fresh List instance every time:

 someList1.add(someList2);
 someMap.put(someKey, someList1);
 someList1 = new List<...>();
 someList1.add(stuff)
 someMap.put(someOtherKey, someList1);

Answer 3

Read through your code:

What you are describing really should not be happening. You should really use a debugger and step through the lines and check if this line of code is actually doing what you are thinking it's doing (ln 57):

clientCode = account.getClientId().getClientCode();

It's very likely an exception triggered before you reached your second row, or there are unexpected duplicate data, etc.

Also, what I said earlier is still valid. At ln 158, instead of doing:

reportDataSubList.clear();

Do

reportDataSubList = new ArrayList<String>();

You also have a lot of unnecessary initialization at the top of your loop.

---

Regarding your comment:

In every iteration of a loop, list gets populated. End of the loop, it gets added to the map and after adding the list gets clear()

I'm surprised this is not breaking anything. All your lists in your map should be empty.

---

If you aren't doing

List a = new ArrayList();

but doing

a.clear();

then it's clear why the list is empty. All your entries are of the same reference.

By declaring

List a = new ArrayList();

you are creating a new instance of List object, and whatever you do to this object will not affect what you have already created.