无法从ArrayList获取值

Question

I have an ArrayList which takes an object.

Handler.java

public ArrayList<LinkedInAccountObject> getAllLinkedInUsersFromDatabase(){

    LinkedInAccountObject lao = new LinkedInAccountObject();
    counter++;
    lao.setAccountId(rs.getLong("account_id"));

    lao.setLinkedInAccountId(rs.getString("linkedin_account_id"));
    lao.setParentId(rs.getLong("parent_id"));
    lao.setFirstName(rs.getString("first_name"));

    lao.setLinkedInAccountId(rs.getString("linkedin_account_id"));
    lao.setEmail(rs.getString("email"));
    lao.setAccessToken(rs.getString("access_token"));
    lao.setExpiresOn(rs.getLong("expires_on"));

    laoarray.add(counter, lao);
}

My PageLoader.java uses this object to set values

ArrayList<LinkedInAccountObject> laoarray = lndb.getAllLinkedInUsersFromDatabase();

    for (LinkedInAccountObject lao : laoarray) {
    LinkedInPageObject lpo = new LinkedInPageObject();
    lpo.setCompanyID(lao.getParentId());
    lpo.setComment(lao.getComment());
    //lpo.setDescription(obj.getString("description"));
    //lpo.setTitle(obj.getString("title"));
    }

But im unable to use the lao object to get the details, getting an null pointer.

when i print the lao object, it gives the result as below,

array objects[null, LinkedInAccountObject [accountId=xxx, parentId=xx, expiresOn=xxx]]

Answer 1

I would suggest that you replace your loop in the second code with the following:

Iterator<LinkedInAccountObject> iterator = laoarray.iterator();
while(iterator.hasNext()){
    LinkedInAccountObject lao = iterator.next()
    LinkedInPageObject lpo = new LinkedInPageObject();
    lpo.setCompanyID(lao.getParentId());
    lpo.setComment(lao.getComment());
    //remaining of your code.
}

EDIT

From all the comments that have been posted here I feel that you have initialised the counter variable as 0 . In your method getAllLinkedInUsersFromDatabase() you are looping through a loop using rs.hasNext() . Now if this is correct, Then when the first data is being stored, your method creates a new instance of LinkedInAccountObject in lao . Then it goes on to increment counter by 1 . So in this case counter was 0 now it becomes 1 .

After all your code that you uploaded being executed in the last line it executes laoarray.add(counter, lao); . Here counter being at 1 adds the lao object to the laoarray at position index 1, leaving position index 0 as null . Then it repeats till the end of the ResultSet . This means if your rs variable returned 10 rows, they would be added to laoarray in indices 1 to 10 with 0 index being null.

You could verify if this is happening or not by simply System.out.println("laoarray length = "+laoarray.size()); in your 'PageLoader.java' after you have initialised the laoarray variable.

If this is correct then you could remove the counter++; in the method getAllLinkedInUsersFromDatabase() from its present location and set it after laoarray.add(counter, lao); as shown below:

LinkedInAccountObject lao = new LinkedInAccountObject();
//counter++; remove it from here.
lao.setAccountId(rs.getLong("account_id"));

lao.setLinkedInAccountId(rs.getString("linkedin_account_id"));
lao.setParentId(rs.getLong("parent_id"));
lao.setFirstName(rs.getString("first_name"));

lao.setLinkedInAccountId(rs.getString("linkedin_account_id"));
lao.setEmail(rs.getString("email"));
lao.setAccessToken(rs.getString("access_token"));
lao.setExpiresOn(rs.getLong("expires_on"));

laoarray.add(counter, lao);
counter++;//place it here

Answer 2

Does you counter start at -1? You do counter++ before adding to the arraylist. This would mean that the first entry is never filled.

You could edit the code to start at index 0, or in the for loop check if the lao isen't null before handeling it.

Answer 3

This code doesn't seem complete but my guess is that you modify counter before adding the item so if you have an array and start with counter = 0 you add the first element to position 1 and position 0 remains null.

Make it:

LinkedInAccountObject lao = new LinkedInAccountObject();
.... fill object values ......
laoarray.add(counter, lao);
counter++;