android function in class throws java.lang.NullPointerException

I've mad开发者_C百科e a class which holds some string and integers, in that class I made a function to convert the data in the class in to a readable string;

    public String GetConditions() {
        String BigString = null;
        String eol = System.getProperty("line.separator");  
        try {
            BigString += "Depth: " + ci(Depth) + eol;

and so on...

Because I have to convert many integers, I made an extra function to convert a integer to a string;

public String ci(Integer i) { 
    // convert integer to string
    if (i != null) {
        String a = new Integer(i).toString();
    return  a;
    } else {
    return "n/a";
    }
}

This throws a NullPointerException exception on return a. I'm quite new to Java, this is probally a noob question... Sorry about, thanks in advance!

There is a much simpler way to convert an Integer to a String: use String#valueOf(int).

public String ci(Integer i)
{
    return i == null ? "n/a" : String.valueOf(i);
}

Try converting the Integer you pass in your method to string, instead of instantiating a new one.

You can do it straight forward like:

String a = i.toString();

or

String a = Integer.toString(i.intValue());

Thanks guys, but I found the problem, I've tried to add something to a string which was 'null' , this line:

String BigString = null;