Remove Empty String array from ArrayList

Question

I am trying to remove empty a String array from ArrayList:

 List<String[]> someList = new ArrayList<String[]>();

which contains data like:

[
 { "Loic" , "Remy" , "Fail","Medical"} ,
 { "Faser" , "Foster" , "Pass","Southampton","GK","Young"} ,
 { "" , "" ,} ,
 { "" , "" , "","","",""} ,
 { "Emre" , "Can" , "Pass","Liverpool","CDM"}
]

I want to remove the empty String[] from the ArrayList:

List<String[]> someList = (List<String[]>) csvMappedData.get(Constants.CSV_DATA);
 //Clone to new Array List
 List<String[]> cloneCSV = new ArrayList<String[]>(someList);
 for (String[] csvSingleLine : cloneCSV) {
 //Create New List of String only
 List<String> strings = new ArrayList<String>(Arrays.asList(csvSingleLine));
 //Remove all string that are null or blank
 strings.removeAll(Arrays.asList(null, ""));
 //Check if the List is empty or null after removing in above step
 if (strings.isEmpty() || Validator.isNull(strings)) {
 //If yes it is all blank String array 
 //Remove from orginal LIST
 someList.remove(csvSingleLine);
 }
 }

The above code is working fine for me.

Questions:

1. Is there any other alternative solution that is quick and elegant?
2. What are the change that I could make to it, to make it more efficient?

The size of each row varies, so I couldn't use remove all by creating a dummy array.

• Cruncher: I'd like to mention, that the excessive commenting actually makes this less readable.
• Runcorn: Yes, in my development environment, i don't use comments that often....except for the javadoc. But i commented it out here so , i can elaborate what i have done in the code.
• Simon Forsberg: @Runcorn We can always see what you are doing, the code will tell us that. Your comments should explain why you are doing it.

Answer 1

There are a few tricks you can use to improve this code.

First of all,

List<String[]> someList = (List<String[]>) csvMappedData.get(Constants.CSV_DATA);
List<String[]> cloneCSV = new ArrayList<String[]>(someList);
for (String[] csvSingleLine : cloneCSV) {

I understand that you're using this "copy the list"-approach to avoid a ConcurrentModificationException, but instead of doing that you can use an Iterator.

List<String[]> someList = (List<String[]>) csvMappedData.get(Constants.CSV_DATA);
Iterator<String[]> iterator = someList.iterator();
while (iterator.hasNext()) {
 String[] strings = iterator.next();
 if (stringsShouldBeRemoved) {
 iterator.remove();
 }
}

---

Now, as for your code to check for whether to remove a String[]:

List<String> strings = new ArrayList<String>(Arrays.asList(csvSingleLine));
strings.removeAll(Arrays.asList(null, ""));
if (strings.isEmpty() || Validator.isNull(strings)) {
 someList.remove(csvSingleLine);
}

Again, you're using a copying-approach. To check for whether or not an object fulfills a criteria, you don't need to copy it, modify it, and check if it fulfills another criteria. Copying it and modifying it makes it slower and uses more memory.

Instead, let's use a method:

boolean shouldRemoveCSVSingleLine(String[] csvSingleLine) {
 for (String str : csvSingleLine) {
 if (str != null && !str.equals("")) {
 return false;
 }
 }
 return true;
}

Now you can use this method in the while(iterator.hasNext()) loop:

List<String[]> someList = (List<String[]>) csvMappedData.get(Constants.CSV_DATA);
Iterator<String[]> iterator = someList.iterator();
while (iterator.hasNext()) {
 String[] strings = iterator.next();
 if (shouldRemoveCSVSingleLine(strings)) {
 iterator.remove();
 }
}

• Runcorn: Thanks @Smion , i agree with you in the most of the reasoning you stated , except for checking the empty array. for (String str : csvSingleLine) { , wouldn't it be better to use csvSingleLine.removeAll(Arrays.asList(null, "")); ?
• Simon Forsberg: @Runcorn That depends, if you have the data { "Faser", "Foster", "Pass", "", "", "Young"} would you want it to be modified into { "Faser", "Foster", "Pass", "Young"} ?

Answer 2

The removal code can be done in 1 line using the Java 8 Stream API, though I'm sure Simon's answer has better performance.

static List<String[]> removeEmptyStringArrays(List<String[]> strArrays) {
 return strArrays
 .stream()
 .filter(strArray -> !isEmptyStringArray(strArray))
 .collect(Collectors.toList());
}
static boolean isEmptyStringArray(String[] strArray) {
 for(String str : strArray) {
 if(str != null && !str.equals("")) {
 return false;
 }
 }
 return true;
}

• 200_success: You could just write if (!"".equals(str)) { return false; }.
• Simon Forsberg: Speaking of Java 8, it's even possible to do return Arrays.stream(args).allMatch(!"".equals(str)); in the isEmptyStringArray method, which makes it easier to inline it inside the .filter lambda directly.