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1

How to remove null value from String array in java?

String[] firstArray = {"test1","","test2","test4",""};

I need the "firstArray" without null ( empty) values like this

String[] firstArray = {"test1","test2","test4"};
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13  
null is completely different from "empty string" in Java. That's your first problem. – JSBձոգչ Nov 10 '10 at 23:55
null is not "". "" is an empty, but perfectly valid string. – EboMike Nov 10 '10 at 23:55
There is no null value in that array. There is, however, an empty sting (a non-null String object with a length of 0). Anyway, what have you tried? – pst Nov 10 '10 at 23:55
yes you are right. null is different from "". just i wanted to removed all empty strings and should get another "String Array" without Empty strings as i mentioned. – Gnaniyar Zubair Nov 11 '10 at 0:00
Then you might want to update your question to reflect the fact that you mean empty string and not null. – Steve Kuo Nov 11 '10 at 0:11
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4 Answers

up vote 9 down vote accepted

If you want to avoid fencepost errors and avoid moving and deleting items in an array, here is a somewhat verbose solution that uses List:

import java.util.ArrayList;
import java.util.List;

public class RemoveNullValue {
  public static void main( String args[] ) {
    String[] firstArray = {"test1", "", "test2", "test4", "", null};

    List<String> list = new ArrayList<String>();

    for(String s : firstArray) {
       if(s != null && s.length() > 0) {
          list.add(s);
       }
    }

    firstArray = list.toArray(new String[list.size()]);
  }
}

Added null to show the difference between an empty String instance ("") and null.

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thanks this is working fine – Gnaniyar Zubair Nov 11 '10 at 0:27
up vote 9 down vote

If you actually want to add/remove items from an array, may I suggest a List instead?

String[] firstArray = {"test1","","test2","test4",""};
ArrayList<String> list = new ArrayList<String>();
for (String s : firstArray)
    if (!s.equals(""))
        list.add(s);

Then, if you really need to put that back into an array:

firstArray = list.toArray(new String[list.size()]);
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Haha. You implemented what I described! :-) My one improvement would be to pass a new String[0] to the toArray though -- it will create a new array with the correct size as needed. – pst Nov 11 '10 at 0:04
You should use String.isEmpty() instead of String.equals("") – Steve Kuo Nov 11 '10 at 0:11
thanks this is working fine – Gnaniyar Zubair Nov 11 '10 at 0:28
@Steve, lots of people feel the way you do. I just (personally) think that s.equals("") is more readable -- less abstract. – Kirk Woll Nov 11 '10 at 1:04
@DaveJarvis, it's rather self-evident that the OP was confusing the empty string with null. – Kirk Woll Aug 11 '12 at 13:45
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up vote 0 down vote

Those are zero-length strings, not null. But if you want to remove them:

firstArray[0] refers to the first element
firstArray[1] refers to the second element

You can move the second into the first thusly:

firstArray[0]  = firstArray[1]

If you were to do this for elements [1,2], then [2,3], etc. you would eventually shift the entire contents of the array to the left, eliminating element 0. Can you see how that would apply?

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1  
Then the question becomes: "How can you resize an Array in Java"? :-) – pst Nov 10 '10 at 23:58
That doesn't really do what he wants. This just copies data around. It doesn't do anything to make the array smaller. – mlathe Nov 11 '10 at 0:00
The point was to get him going in the right direction. – Falmarri Nov 11 '10 at 0:01
thanks. But if i know the position where empty will come, i can do as u said. But empty strings generating dynamically. I cant predict in which position empty ( zero-length) will come. – Gnaniyar Zubair Nov 11 '10 at 0:01
Yes, but s.size() == 0 will tell you a string is zero-length. The idea was for you to iterate through the array shifting elements over zero-length elements. The question was so trivial I assumed it was homework and didn't want to give you the whole answer, but apparently that's what's getting voted up. shrug – Mud Nov 11 '10 at 2:51
up vote 0 down vote

Using Google's guava library

String[] firstArray = {"test1","","test2","test4","",null};

Iterable<String> st=Iterables.filter(Arrays.asList(firstArray),new Predicate<String>() {
    @Override
    public boolean apply(String arg0) {
        if(arg0==null) //avoid null strings 
            return false;
        if(arg0.length()==0) //avoid empty strings 
            return false;
        return true; // else true
    }
});
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2  
Along the same approach, one could use the FunctionalJava library. – pst Nov 11 '10 at 22:00
@Emil And then, how do you put what is inside st back inside firstArray? – Abdull Feb 20 at 1:28
@Abdull: No need for that since firstArray is not modified.The filtering happen's lazily.i.e while iterating the array. – Emil Feb 20 at 6:10

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