Removing unfilled values or null values from array of String in Java [duplicate]

Question

I have following String Array tmp = [null, null, null, Mars, Saturn, Mars] coming after doing the operation - allSig[d3].split(" "); where allSig is an array of Strings. The null value is empty value in the array. Now I want to remove the null. For this I am using

tmp[indexNumber] != null is not working and giving true ; taking null as the value. Even if i am using "null" as a string is not working.

How to remove this.

public static String[] removeElements(String[] allElements) {
    String[] _localAllElements = new String[allElements.length];

    for (int i = 0; i < allElements.length; i++)
        if (allElements[i] != null)
            _localAllElements[i] = allElements[i];

    return _localAllElements;
}

No First i created a array by this way - String[] x= new String[10]; then I added in the value by this way - x[a8] += " " + planetName1Tr[a9]; in this scenario in null value is added that is lyk - "null Sun Moon" etc. Now I want to remove this null. — Kumar
– Kumar, Commented Aug 17, 2012 at 8:32

obataku · Accepted Answer · 2012-08-18 19:14:07Z

2

public static String[] clean(final String[] v) {
  int r, w;
  final int n = r = w = v.length;
  while (r > 0) {
    final String s = v[--r];
    if (!s.equals("null")) {
      v[--w] = s;
    }
  }
  return Arrays.copyOfRange(v, w, n);
}

or

public static String[] clean(final String[] v) {
  int r, w, n = r = w = v.length;
  while (r > 0) {
    final String s = v[--r];
    if (!s.equals("null")) {
      v[--w] = s;
    }
  }
  final String[] c = new String[n -= w];
  System.arraycopy(v, w, c, 0, n);
  return c;
}

Works fine...

public static void main(final String[] argv) {
  final String[] source = new String[] { "Mars", "null", "Saturn", "null", "Mars" };
  assert Arrays.equals(clean(source), new String[] { "Mars", "Saturn", "Mars" });
}

edited Aug 18, 2012 at 19:14

answered Aug 17, 2012 at 8:37

obataku

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Comments

Denys Séguret · Accepted Answer · 2012-08-17 08:48:13Z

2

You're creating an array with same size as the original one. So it's the same as the original array, as you copy non null values and default values are null.

Do this :

public static String[] removeElements(String[] allElements) {
    // 1 : count
    int n = 0;
    for (int i = 0; i < allElements.length; i++)
        if (allElements[i] != null) n++;

    // 2 : allocate new array
    String[] _localAllElements = new String[n];

    // 3 : copy not null elements
    int j = 0;
    for (int i = 0; i < allElements.length; i++)
        if (allElements[i] != null)
            _localAllElements[j++] = allElements[i];

    return _localAllElements;
}

edited Aug 17, 2012 at 8:48

answered Aug 17, 2012 at 8:30

Denys Séguret

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6 Comments

obataku Over a year ago

No reason at all for doing 2 passes.

Denys Séguret Over a year ago

@veer you need the number of not null strings to allocate a well sized array. Or you need to do another copy after, which is more expensive.

obataku Over a year ago

you only have to check for null once!

obataku Over a year ago

actually Arrays.copyOf is probably as fast as the manual copy you're doing, not to mention you'd have to compare each element against "null" twice ;)

Denys Séguret Over a year ago

You're changing the initial array. I don't. That's the reason you seem to make only one copy operation. But this is a detail.

|

IvanRF · Accepted Answer · 2016-02-18 20:28:41Z

2

Abstracting @az answer, this applies to any class type:

@SuppressWarnings("unchecked")
public static <T> T[] clean(T[] a) {
    List<T> list = new ArrayList<T>(Arrays.asList(a));
    list.removeAll(Collections.singleton(null));
    return list.toArray((T[]) Array.newInstance(a.getClass().getComponentType(), list.size()));
}

answered Feb 18, 2016 at 20:28

IvanRF

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Comments

Jon Newmuis · Accepted Answer · 2012-08-17 08:37:19Z

If you want the array to contain only the non-null values (i.e. the resulting array would be ["Mars", "Saturn", "Mars"]), then I would look at this as a two part problem.

First, you must identify what the size of the new array should be. From inspection, it's easy to see that it's 3, but you will need to need to count them to calculate this programmatically. You can do this by saying:

// Calculate the size for the new array.
int newSize = 0;
for (int i = 0; i < allElements.length; i++)    {
    if (allElements[i] != null) {
        newSize++;
    }
}

Secondly, you will need to create a new array with that size. Then you can put all of the non-null elements into your new array, as you have done above.

// Populate the new array.
String[] _localAllElements = new String[newSize];
int newIndex = 0;
for (int i = 0; i < allElements.length; i++) {
    if (allElements[i] != null) {
        _localAllElements[newIndex] = allElements[i];
        newIndex++;
    }
}

// Return the new array.
return _localAllElements;

You can just combine these two components as the new content of your results method. See the full combined code and live sample output here.

sloth · Accepted Answer · 2012-08-17 09:54:53Z

0

public static String[] removeElements(String[] allElements) {
    String[] _localAllElements = new String[allElements.length];
    int j = 0;
    for (int i = 0; i < allElements.length; i++)
        if ( allElements[i] != null && !allElements[i].equals(""))
            _localAllElements[j++] = allElements[i];

    return _localAllElements;
}

edited Aug 17, 2012 at 9:54

sloth

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answered Aug 17, 2012 at 8:49

vincent.lee

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1 Comment

Christos Papoulas Over a year ago

this is not working, it leaves null strings at the end of the new String Array if null or "" is found

Clint Eastwood · Accepted Answer · 2018-03-19 18:02:59Z

0

This is a very old question but this Java 8+ solution might be useful to someone:

public static String[] removeElements(String[] allElements) { return Arrays.stream(allElements) .filter(Objects::nonNull) .collect(Collectors.toArray()); } or if you, like me, are a fan of readable code and don't want static methods to get in your way, you can simplify this even further using static imports:

public static String[] removeElements(String[] allElements) { return stream(allElements).filter(Objects::nonNull).collect(toArray()); }

answered Mar 19, 2018 at 18:02

Clint Eastwood

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1 Comment

Holger Over a year ago

There is no Collectors.toArray(). To get a String[] from a Stream, you have to invoke .toArray(String[]::new) directly on the Stream.

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