复制字符串数组并删除空字符串

Question

I want to eliminate empty elements within my String array. This is what I have tried so far:

String version = null; 
String[] xml = new String[str.length]; 
for(int i = 0; i <= str.length -1; i++)
{
    if(str[i] == "")
    {

    }
    else
    {
        xml[i] = str[i]; 
    }
}

String version = null; 
String[] xml = new String[str.length]; 
for(int i = 0; i <= str.length -1; i++)
{
    if(!str[i].equals(""))
    {
        xml[i] = str[i]; 
    }
}

String version = null; 
String[] xml = new String[str.length]; 
for(int i = 0; i <= str.length -1; i++)
{
    if(!str[i].isEmpty())
    {
        xml[i] = str[i]; 
    }
}

String version = null; 
String[] xml = new String[str.length]; 
for(int i = 0; i <= str.length -1; i++)
{
    if(str[i].isEmpty() == false)
    {
        xml[i] = str[i]; 
    }
}

No matter which one I try, it always copies all the values. I've checked the locals, and it is clear that there are empty arrays within the String array.

Answer 1

Try this,

b = Arrays.copyOf(a, a.length);

Or

b = new int[a.length];
System.arraycopy(a, 0, b, 0, b.length);

Or

b = a.clone();

Answer 2

You are copying the same length array and using the same indexes. The length is always going to be the same.

List<String> nonBlank = new ArrayList<String>();
for(String s: str) {
    if (!s.trim().isEmpty()) {
        nonBlank.add(s);
    }
}
// nonBlank will have all the elements which contain some characters.
String[] strArr = (String[]) nonBlank.toArray( new String[nonBlank.size()] );

Answer 3

这是将数组复制到新数组的最佳且简短的方法。

System.arraycopy(srcArray, 0, destArray, 1, destArray.length -1);

Answer 4

String str[] = {"Hello","Hi","","","Happy","","Hmm"};
    int count = 0;// Thisreprents the number of empty strings in the array str
    String[] xml = new String[str.length]; 
    for(int i = 0,j=0; i <= str.length -1; i++)
    {
        if(str[i].equals(""))
        {
            count++;
        }
        else
        {
            xml[j] = str[i];j++; 
        }
    }
    String a[] = Arrays.copyOfRange(xml, 0, xml.length-count);//s is the target array made by copieng the non-null values of xml
    for(String s:a){
        System.out.println(s);
    }

NOTE : This may not be an efficient solution but it will give the result as per your requirement

Answer 5

This is just an alternate solution since you didn't want ListArray . Read the comments in the code to clearly understand the logic.

int i,j=0,cnt=0;

//The below for loop is used to calculate the length of the xml array which
//shouldn't have any empty strings.

for(i=0;i<str.length;i++)
if(!isEmpty(str[i])
cnt++;

//Creation of the xml array with proper size(cnt) and initialising i=0 for further use
String xml[]=new String[cnt];
i=0;

//Simply copying into the xml array if str[i] is not empty.Notice xml[j] not xml[i]
while(i<str.length)
{
if(!isEmpty(str[i]))
{
xml[j]=str[i];
i++;
j++;
}
else
i++;
}

That should do the work. Also I would suggest to not work with the 0th position of array as it kinda creates confusion for .length functions.Thats only my view. If you are comfortable with it,carry on! :D

Answer 6

If you are looking for a high-performance solution I think that this is the best solution. Otherwise if your input array is not so huge, I would use a solution similar to Peter Lawrey one, so it makes your code easy to understand.

With this solution you loop the input array only one, and if you don't need the input array any more you can avoid one array copy calling filterBlankLines with preserveInput = false.

public class CopyingStringArrayIntoNewStringArray {


public static void main(String[] args) {

    String[] str =  { "", "1", "", null, "2", "   ", "3", "" };

    System.out.println("\nBefore:");
    printArrays(str);

    String[] xml = filterBlankLines(str, true);

    System.out.println("\nAfter:");
    printArrays(xml);

}

private static String[] filterBlankLines(String input[], boolean preserveInput ) {

    String[] str;
    if (preserveInput) {
        str = new String[input.length];
        System.arraycopy(input, 0, str, 0, input.length);
    } else {
        str = input;
    }

    // Filter values null, empty or with blank spaces
    int p=0, i=0;
    for (; i < str.length; i++, p++) {
        str[p] = str[i];
        if (str[i] == null || str[i].isEmpty() || (str[i].startsWith(" ") && str[i].trim().isEmpty())) p--;
    }

    // Resize the array
    String[] tmp = new String[ p ];
    System.arraycopy(str, 0, tmp, 0, p);
    str = null;

    return tmp;
}

private static void printArrays(String str[]) {

    System.out.println( "length " + str.length);
    for (String s : str ) {
        System.out.println(">"+s+"<");
    }

}

}

The output:

Before:
length 8
><
>1<
><
>null<
>2<
>   <
>3<
><

After:
length 3
>1<
>2<
>3<