java-Declaring Array Based on If Statement

Question

I was wondering if there is any way to declare an array of different sizes depending on if an if statement condition is met. However, after typing in this code into NetBeans:

if(winner == true)
    double data[][] = new double[16][5];
else
    double data[][] = new double[14][5];

I receive an error message stating: Variable declaration not allowed here.

Why is this not allowed? Is there any way to accomplish what I am trying to do? Tia.

NOTE

As was made clear in the answers provided, I was not considering scope when writing this post. I apologize. Thanks to everyone who provided helpful solutions and insight.

declare the reference outside the if and initialize it inside — Jason White
– Jason White, Commented Apr 10, 2017 at 14:39
the issue is that you have a single lined code scope that declares and assigns a scope local variable. That variable will fall out of scope immediately after you set it, so the IDE assumes you made some mistake. — Wietlol
– Wietlol, Commented Apr 10, 2017 at 14:40
You can also: double data[][] = new double[winner? 16 : 14][5]; — Oneiros
– Oneiros, Commented Apr 10, 2017 at 14:40
Can someone elaborate as to why I am getting down voted for this? — John
– John, Commented Apr 10, 2017 at 14:49
Because your code makes obivously not a single bit of sense. What do you expect to do with a variable which will be removed after the if/else block? — Tom
– Tom, Commented Apr 10, 2017 at 14:50

Sweeper · Accepted Answer · 2017-04-10 14:40:29Z

13

An alternative solution would be:

double data[][] = new double[winner ? 16 : 14][5];

The x ? a : b thing is called a "ternary operator". It evaluates to a if x is true, otherwise b.

answered Apr 10, 2017 at 14:40

Sweeper

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Comments

Ishnark · Accepted Answer · 2017-04-10 14:39:18Z

5

You should do :

double data[][]; 
if(winner == true)  // or just --> if (winner)
    data = new double[16][5];
else
   data = new double[14][5];

Essentially, when you declare it in the if, you can only use it in the if. It's scope is limited to that if.

answered Apr 10, 2017 at 14:39

Ishnark

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Comments

dumbPotato21 · Accepted Answer · 2017-04-10 14:54:53Z

2

The Arrays you declare are inside an if function where they arent used again, im not sure if thats the reason for your error but maybe declare the var outside the IF statement

double data[][];

if(winner == true){
    data = new double[16][5];
}else{
    data = new double[14][5];
}

edited Apr 10, 2017 at 14:54

dumbPotato21

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answered Apr 10, 2017 at 14:40

Lukas A

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Comments

Bill the Lizard · Accepted Answer · 2017-04-10 14:39:41Z

1

You don't want to declare a variable inside an if block because it will be out of scope as soon as you exit that block. Declare the variable before the if, then initialize it inside.

double data[][];

if(winner == true)
    data = new double[16][5];
else
    data = new double[14][5];

answered Apr 10, 2017 at 14:39

Bill the Lizard

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Comments

KOUSIK MANDAL · Accepted Answer · 2017-04-10 14:49:07Z

1

Inside if statement only statements are allowed, but A declaration is not a statement, so it's not allowed in that spot.

Ok, just try in this way;

double data[][];
if(winner)
   data=new double[16][5];
else
   data=new double[14][5];

edited Apr 10, 2017 at 14:49

answered Apr 10, 2017 at 14:43

KOUSIK MANDAL

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Comments

Youcef LAIDANI · Accepted Answer · 2017-04-10 14:49:37Z

1

You have to declare your array outside your if..else block and initialize it inside your if..else blocks:

double data[][];

if(winner == true)
    data = new double[16][5];
else
    data = new double[14][5];

edited Apr 10, 2017 at 14:49

answered Apr 10, 2017 at 14:39

Youcef LAIDANI

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3 Comments

Aaron Over a year ago

If you want to be paranoid, it's certainly because one of the other posters isn't fairplay and wants his own solution to be above yours ! Honestly I'd suggest deleting your answer which doesn't provide more than the 3 above, getting rid of the downvote in the process. I suggest it to you because you've got the downvote, but I totally agree all these answers are equal ; it's just stupid to see the same answer 3 times

DanielBarbarian Over a year ago

Could it be because of the brackets during assignment? I get unexpected token on the declaration lines. If I change data[][] = new double[16][5]; to data = new double[16][5]; it goes through fine.

Youcef LAIDANI Over a year ago

oh yes this is maybe the reason its my bad i already fix it @DanielBarbarian thank you for the help

Housekeeping · Accepted Answer · 2017-04-13 17:18:37Z

1

Try this:

double data[][];
if(winner)
     data = new double[16][5];
else
     data = new double[14][5];

edited Apr 13, 2017 at 17:18

Housekeeping

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answered Apr 10, 2017 at 14:40

Hadi

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Comments

Eddie Martinez · Accepted Answer · 2017-04-10 14:52:11Z

0

This is a perfect opportunity to use a ternary operator.

double data[][] = (isWinner)?new double[16][5] : new double[14][5];

Suggestions

Name your boolean variable isWinner instead of winner and you can perform the check like the example above. By removing the condition winner == true your code becomes easier to read.
Use the ternary operator, it makes your code shorter and clearer to read.

edited Apr 10, 2017 at 14:52

answered Apr 10, 2017 at 14:44

Eddie Martinez

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Comments

comanitza · Accepted Answer · 2017-04-10 14:55:11Z

-2

It's an old corner cases, add curly braces as you always should:

        if(winner == true) {
            double data[][] = new double[16][5];
        }
        else {
            double data[][] = new double[14][5];
        }

This is due to the fact that you statements are local variable declaration statements. This behaviour is described in Java Puzzlers and it's covered in the JLS section 14.4.

edited Apr 10, 2017 at 14:55

answered Apr 10, 2017 at 14:40

comanitza

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9 Comments

Aaron Over a year ago

There won't be any error anymore, but the error was there for a good reason

Tom Over a year ago

So instead of fixing the error, you prefer to "hide" it? Clever.

Tom Over a year ago

Your code makes as less sense as OPs code, because you still create a useless variable.

Aaron Over a year ago

The error is that declaring a variable as the only "statement" of a block is totally useless since it will be out-of-scope and garbaged collected just after having been created. The not-exactly-a-statement property of variable declaration prevents you from doing this mistake with single line then/else blocks, which you can avoid by using brackets, but you'll still be declaring a dead variable

Aaron Over a year ago

@comanitza I thought you had a point, but OP's first sentence clearly states that he want to declare an array of variable size depending on a condition. That makes me assume he will want to use this array afterward, and people downvoting you probably found this obvious too.

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