Java: How can i remove null value from a string?

Question

When this code is run, it outputs nullhi. Why is it doing this?

public static void main(String[] args) {
    String[] a = new String[1];
    String m = null;
    String c = "hi";
    for (int i = 0 ; i < c.length() ; i++){
        a[0] = a[0] + c.charAt(i);  
    }
    System.out.print(a[0]);
}

Relevant: http://stackoverflow.com/questions/3426843/what-is-the-default-initialization-of-an-array-in-java — Oli, Mar 16 '15 at 14:30

score 4 · Answer 1 · answered Mar 16 '15 at 14:29

4

Before the loop, write:

a[0] = "";

i.e.

public static void main(String[] args) {
String[] a= new String[1];
String m = null;
String c = "hi";

a[0] = "";

for (int i=0 ; i<c.length() ; i++){
    a[0]=a[0]+c.charAt(i);  
}

System.out.print(a[0]);

}

answered Mar 16 '15 at 14:29

Dermot Blair

1,600
10
10

@Angelb - In addition, the variable `a` does not need to be an array. You may have heard that Java Strings are immutable. This is true. However, in the expression `String a = ""`, the variable `a` is not a String -- it is a mutable reference to a String. – Andy Thomas Mar 16 '15 at 14:47

Muneeb Nasir · Answer 2 · 2015-03-16T14:55:16.077

0

Do this

    for (int i=0 ; i<c.length() ; i++){
      a[i] = "";
      a[i]= c.charAt(i);  

    }

what you are doing is

for (int i=0 ; i<c.length() ; i++){
    a[0]=a[0]+c.charAt(i);  // a[0] is null, 
}

edited Mar 16 '15 at 14:55

answered Mar 16 '15 at 14:33

Muneeb Nasir

2,414
4
31
54

score -1 · Answer 3 · answered Mar 16 '15 at 14:30

-1

Test if string is null

a[0] = ((a[0] == null) ? "" : a[0] ) + c.charAt(i);

answered Mar 16 '15 at 14:30

Rene M.

2,660
15
24

`a[0]` will always be `null` until it is explicitly changed. That is how object arrays are initialized. – Oli Mar 16 '15 at 14:31
Whats going on here? This solution removes the null in the output because a[0] is checked on null. Learn programming before downvoting correct answers – Rene M. Mar 16 '15 at 14:46
I didn't downvote you, but why not just have `a[0] = "";` before the loop instead of checking it every time? – Oli Mar 16 '15 at 14:49
Both correct and not the question. All fine, only understand sometimes not the reactions of people here. I think twice before I don't vote something. – Rene M. Mar 16 '15 at 15:14

Java: How can i remove null value from a string?

3 Answers3