Question

Hi i encountered this problem whereby when i initialized my String[], there seems to be a null in the String[] before i do anything. How do i initialized the String[] to be completely empty,i.e. without the null at the start?
The output for the following code is:


nullABC

nullABC

nullABC

nullABC

nullABC


public static void main(String[] args){
    String[] inputArr = new String[5];
    for (int i = 0; i< inputArr.length; i++){
        inputArr[i] += "ABC";
    }
    for (int i = 0; i< inputArr.length; i++){
        System.out.println(inputArr[i]);
    }
}

}

Answer 1

A null reference is about as empty as a string array element can be. Note that there’s a big difference between a reference to the empty string and a null reference though. Just change your code to use simple assignment instead of +=.

for (int i = 0; i< inputArr.length; i++){
    inputArr[i] = "ABC";
}

If you need to do conditional concatenation elsewhere, use something like this:

for (int i = 0; i< inputArr.length; i++) {
    String current = inputArr[i];
    String suffix = "ABC";
    String replacement = current == null ? suffix : current + suffix;
    inputArr[i] = replacement;
}

Alternatively, you could use something like this:

public static String emptyForNull(String x) {
    return x == null ? "" : x;
}

and then have:

for (int i = 0; i< inputArr.length; i++){
    inputArr[i] = emptyForNull(inputArr[i]) + "ABC";
}

Or (yes, lots of available options):

public static String nullAwareConcat(String x, String y) {
    return x == null && y == null ? ""
        : x == null ? y
        : y == null ? x
        : x + y;
}

...

for (int i = 0; i< inputArr.length; i++){
    inputArr[i] = nullAwareConcat(inputArr[i], "ABC");
}