Question

I have an array:

[0, 5, 6, 0, 0, 2, 5]

I would like to remove all zeros from it, so that this returns (keeping the same order):

[5, 6, 2, 5]

Is there any easier way to remove all zeros than the following?

int[] array = {0, 5, 6, 0, 0, 2, 5};
        int len = 0;
        for (int i=0; i<array.length; i++){
            if (array[i] != 0)
                len++;
        }
        int [] newArray = new int[len];
        for (int i=0, j=0; i<array.length; i++){
            if (array[i] != 0) {
                newArray[j] = array[i];
                j++;
            }
        }

I haven’t been able to find any method in the Arrays class, and Google/SO searches didn’t give me any good answers.

Answer 1

One loop to either count or filter out the zeros cannot be avoided; however, the second loop can be avoided with the use of System.arraycopy().

This function will make a copy of an existing array into an array of different length, which means that before we use it our array must already be free from zeros. Therefore, in the first loop we cannot just count the zeros, we have to also filter them out. Here is how to actually do it:

int targetIndex = 0;
for( int sourceIndex = 0;  sourceIndex < array.length;  sourceIndex++ )
    if( array[sourceIndex] != 0 )
        array[targetIndex++] = array[sourceIndex];
int[] newArray = new int[targetIndex];
System.arraycopy( array, 0, newArray, 0, targetIndex );
return newArray;