Comparing string array in JAVA

Question

I have the following code within a for loop to see if a string equals a search string:

if(Data.coord[i].equals(Data.search))

I've tested the code with exact values i.e if 1=1 and the rest of the code works fine. It just doesn't like the string comparison. The consol gives out this error:

Exception in thread "main" java.lang.NullPointerException
at highercoursework.Search.main(Search.java:16)
at highercoursework.Main.main(Main.java:16)

Thanks

The array is initialized in a data class: static String[] coord = new String[100]; However if no data is needed for that array its just stored as a null value. — user1627774
– user1627774, Commented Nov 15, 2012 at 10:25
I suggest splitting this row into separate ones so that you can debug this issue from the logs. The nullpointer can be the Data.coord or the Data.coord[i] or even Data.search. the other things is to debug — Leni Kirilov
– Leni Kirilov, Commented Nov 15, 2012 at 10:25

Adam Arold · Accepted Answer · 2012-11-15 10:26:12Z

2

You should compare the constant to your parameter since it can be null.

For example if Data.search is a constant which you are searching for you should do this:

if(Data.search.equals(Data.coord[i]))

In this case you won't end up trying to call methods on a null reference and you won't need unnecessary null checks either.

answered Nov 15, 2012 at 10:26

Adam Arold

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3 Comments

Adam Arold Over a year ago

In that case he has to null check one. But in this case we know that Data.search is a constant.

Brian Agnew Over a year ago

Do we know that ? I'm not sure that's explicit (it looks to me like a user input value or similar)

Adam Arold Over a year ago

I assumed it from the context. May be it is null but I really don't think so.

Brian Agnew · Accepted Answer · 2012-11-15 10:39:27Z

2

You have an unpopulated element in your array i.e.

Data.coord[i]

is null. Note that Data.search could be null, but the equals() method will handle this. You just need to perform the lement check first.

edited Nov 15, 2012 at 10:39

answered Nov 15, 2012 at 10:25

Brian Agnew

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3 Comments

user1627774 Over a year ago

Ahh right, I can't think of a way to avoid this. I could do to ifs first to check if values are null and then only compare none null values?

Adam Arold Over a year ago

Nope you should call equals() on an object you know it exists thus using the form in my answer. This is considered a good practice when comparing objects. Always call equals() on the object you already know is not null if possible.

Hussain Akhtar Wahid 'Ghouri' Over a year ago

i think @AdamArold is absolutely correct , logically it saves you the trouble plus avoids your exception , this is more appropriate approach

Ashwinee K Jha · Accepted Answer · 2012-11-15 10:27:36Z

1

String[] coord = new String[100];

This will mean you can assign something to coord[0] but until you do that coord[0] is null. Hence the null pointer exception.

You can try.

String data= Data.coord[i];
if(data != null && data.equals(Data.search))

answered Nov 15, 2012 at 10:27

Ashwinee K Jha

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Comments

Pierre · Accepted Answer · 2012-11-15 11:22:50Z

1

you can avoid your problem in two ways:

In the case coord[i] should not be null

if (Data.coord[i] != null) {
    if(Data.coord[i].equals(Data.search)) {

    }
} else {
    logger.error("Unexpected Behavior: coord[i] should not be null");
}

Note: You can replace the logger message by a more appropriated code that fit to your requirement.

In the case your your coord[i] can be null

comparing in this way won't throw an exception if Data.coord[i] is null. (Assuming Data.search is a constant and can't bu null) So the rules for this case is: use in priority a String object constant to call the method equals.

if (Data.search.equals(Data.coord[i])) {}

edited Nov 15, 2012 at 11:22

answered Nov 15, 2012 at 11:12

Pierre

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Comments

Community · Accepted Answer · 2017-05-23 11:48:54Z

0

Read this to understand What is a Null Pointer Exception?

if coord[] is initialized properly, value of Data.coord[i] may be null. You can check

if(Data.coord[i] != null && Data.coord[i].equals(Data.search)) {}

edited May 23, 2017 at 11:48

CommunityBot

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answered Nov 15, 2012 at 10:33

vels4j

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Comments

Jagger · Accepted Answer · 2012-11-15 11:04:07Z

0

Try this:

if(DATA != null && Data.coord[i].equals(Data.search))

edited Nov 15, 2012 at 11:04

Jagger

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answered Nov 15, 2012 at 10:28

Sashi Kant

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