ArrayList with empty fileds

Question

I have a problem to handle an Arraylist with empty fields.

As input I have values from an Excel List and there some cells empty (show example).

 Column A  Column B  Column C  Column D 

 Val1      Val2      Val3      Val4 

 Bla1      Bla2      Bla3 

 Hug1      Hug2      Hug3      Hug4 

...

These Values are in an Arraylist so far so good. Now I have a Switch Case where I choose now Column D to work with. The Problem now is that I don’t can handle null fields. These must be removed or get a step over, because my output does not have a null. As I’m trying to do this I got an null pointer exception.

Here is some code:

private Arraylist<ExcelReader> el;

private void doSomething() {

   switch (chooseColumn) {

   // ArrayList is loaded
   //…
   case “D”: 
       // here I want to remove the null fields
       for (int c = 0; c <= el.size(); c++) {
          if(el.get(c).getColumnD().isEmpty()) {
          el.remove(c);
          }
       }
   break;
   // …

}

I’ve tried it at the point where I write it back to a file, but got the null pointer exception. Where is my mistake? What am I doing wrong?

Of course el.get(c).getColumnD().isEmpty()) will be a problem if you have null values. You could check there if you get(c) return null. — AxelH
– AxelH, Commented May 15, 2017 at 10:18
Possible duplicate of How to remove all null elements from a ArrayList or String Array? — AxelH
– AxelH, Commented May 15, 2017 at 10:19
if el.get(c) is the one return null, you can see the duplicate to find really nice solutions. If not, this will require some improvments or a condition to filter those without removing it of the list — AxelH
– AxelH, Commented May 15, 2017 at 10:27

Jayanand Raghuwanshi · Accepted Answer · 2017-05-15 10:23:05Z

2

private Arraylist<ExcelReader> el;

private void doSomething() {

switch (chooseColumn) {

// ArrayList is loaded
//…
case “D”: 
   // here use removeAll to remove all null object
   el.removeAll(Collections.singleton(null));  
   for (int c = 0; c <= el.size(); c++) {
      if(el.get(c).getColumnD().isEmpty()) {
      el.remove(c);
      }
   }
break;
// …

}

answered May 15, 2017 at 10:23

Jayanand Raghuwanshi

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3 Comments

AxelH Over a year ago

Since this is from the duplicate I have posted, you could at least add the source of the answer. Plagiat is not accepted here without the source and some improvement. Also, you forgot to add explanations.

Chris Over a year ago

now I get the java.lang.reflect.InvocationTargetException

Jayanand Raghuwanshi Over a year ago

please share exception stack trace

R. Mittal · Accepted Answer · 2017-05-15 10:20:43Z

1

You should understand that isEmpty() does not check on null values. It only checks if size==0 or not. So for checking null values, you should check on condition getColumnD() != null

answered May 15, 2017 at 10:20

R. Mittal

1266 bronze badges

1 Comment

Chris Over a year ago

I've got to null fields in a row, the first one will be removed the second is showing up

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