Null Pointer Exception in Java when using String Arrays

Question

I have a piece of code where the program compares the value of two arrays of strings. I am getting a java.lang.NullPointerException, even though I initialized both arrays. Here is the relevant code:

String[] functions=new String [inputs+1];
int funCounter=0;
for (int a=0;a<2;a++)
{
    for (int b=0;b<2;b++)
    {
        if (tokenizedString[b].equals(keywords[a])&&keywords[a].equals("add"))
        {
            System.out.println("Yay");
            functions[funCounter]="add";
            funCounter++;
        }
        }
    }

This is where I inialize tokenizedString:

String[] tokenizedString;
    tokenizedString=new String[2];

tokenizedString is added to a Scanner in stream here:

StringTokenizer st = new StringTokenizer(input," ");

And here is where I initialize keywords:

String[] keywords;
    keywords=new String[2];

Any ideas? Thanks!

You've initialized tokenizedString, but have you initialized tokenizedString[0] and tokenizedString[1]? — azurefrog
– azurefrog, Commented Jun 10, 2015 at 20:53
You need to show all the relevant code, and putting values in your arrays is certainly relevant to fixing an NPE. If your error is in your initialization code, we're not going to be able to help if we can't see it. It would also be nice if you would mark the line in your code which is throwing the exception. — azurefrog
– azurefrog, Commented Jun 10, 2015 at 20:55
What is the content of keywords? Did you assign any values as elements of tokenizedString? — fabian
– fabian, Commented Jun 10, 2015 at 20:58

Anshuman · Accepted Answer · 2015-06-10 20:57:43Z

1

While you are accessing tokenizedString[n], the string array will give you the nth element. If the nth element is not initialized, for object arrays it will be defaulted to null.

A better way to avoid null checks in this case will be to switch places of the string values if you are sure that the other one will never be null. So instead of:

 tokenizedString[b].equals(keywords[a])

use:

 keywords[a].equals(tokenizedString[b])

answered Jun 10, 2015 at 20:57

Anshuman

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5 Comments

azurefrog Over a year ago

Even safer would be something like org.apache.commons.lang3.StringUtils#equals().

APCoding Over a year ago

Thanks, it works. I'll check it as correct as soon as it lets me.

Turing85 Over a year ago

Approving this, Yoda does not

APCoding Over a year ago

@azurefrog what is that, and how do I do it?

azurefrog Over a year ago

@APCoding commons.apache.org/proper/commons-lang/javadocs/api-3.4/org/…

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