Why i'm getting a null string when i try to add the splitted string?

Question

I have splited a string and from the recieved string i am trying to form a word everything is comming fine but everytime i get null string in the first index why?

Here is my code:

    String assetClasses = "Gold:Stocks:Fixed Income:Commodity:Interest Rates";
    String[] splits = assetClasses.toString().split(":");

    //System.out.println("splits.size: " + splits.length);
    String ab = null;
for(int i=0; i<splits.length;i++){
    System.out.println(splits[i]);
    ab+=splits[i];
}
System.out.println(ab);

The output:

Gold Stocks Fixed Income Commodity Interest Rates

nullGoldStocksFixed IncomeCommodityInterest Rates

because i want the string to be unique code which is the date that i am talking dynamically to put it in sqlite db for some operation — silverFoxA, Apr 17 '15 at 13:09
@Hell Calling `toString()` on a string doesn't make it unique, it just gives you back a reference to the string that you already had. It's effectively a wasted method call - just use the reference that you already have. — JonK, Apr 17 '15 at 13:20
but adding up all the string gives an unique figure i hope you can see that — silverFoxA, Apr 17 '15 at 13:23

score 5 · Accepted Answer · edited May 23 '17 at 12:23

5

Change String ab = null; to String ab = "";

As a complement, see Concatenating null strings in Java to know what's happening when you use String ab = null;

edited May 23 '17 at 12:23

Community

1
1

answered Apr 17 '15 at 13:04

JFPicard

5,029
3
19
43

3

@Hell: As a minor note, although the above will work, when concatenating strings it is recommended you use `StringBuilder`. – npinti Apr 17 '15 at 13:10
ohh thanks this works for me and i just need the datestring to be one to place it as unique id in my database – silverFoxA Apr 17 '15 at 13:11

score 1 · Answer 2 · answered Apr 17 '15 at 13:44

1

It gives null because in java's String class below is the implementation of valueOf api of String class.

public static String valueOf(Object obj) {
        return (obj == null) ? "null" : obj.toString();
}

answered Apr 17 '15 at 13:44

Archana Mundaye

523
1
5
19

score 0 · Answer 3 · answered Apr 17 '15 at 13:20

Also - String is immutable, so you're creating lot's of unnecessary objects during this method execution. Use mutable StringBuilder instead:

    String assetClasses = "Gold:Stocks:Fixed Income:Commodity:Interest Rates";
    String[] splits = assetClasses.split(":");

    StringBuilder ab = new StringBuilder();
    for (int i = 0; i < splits.length; i++) {
        System.out.println(splits[i]);
        ab.append(splits[i]);
    }
    System.out.println(ab.toString());

score 0 · Answer 4 · edited May 23 '17 at 11:59

Let me stress on what npinti said. Strings are immutable in java. Which means every time you say ab+=splits[i]; you are creating a new string. Which is a really slow and inefficient process.

Instead, you can;

String assetClasses = "Gold:Stocks:Fixed Income:Commodity:Interest Rates";
String[] splits = assetClasses.toString().split(":");

//System.out.println("splits.size: " + splits.length);
StringBuilder ab = new StringBuilder();
for(int i=0; i<splits.length;i++){
    System.out.println(splits[i]);
    ab.append(splits[i]);
}
System.out.println(ab.toString());

Its that simple!

Why i'm getting a null string when i try to add the splitted string?

4 Answers4

Linked