How do I define an array with multiple values?

Question

I am doing some Junit testing on my code, which is meant to produce an arraylist of n prime numbers. I want to compare the created list to a list of known prime numbers in an array, and to do this I need to insert multiple values into an array in my testing class.

So what I have at the moment is

int knownPrimes[] = new int[50];

I know that I could insert values into this array by typing

knownPrimes[1] = 2;
knownPrimes[2] = 3;
etc etc.

I was just wondering how I would do this all in one big chunk, maybe something like:

knownPrimes[] = {2,3,5,7,9...};

but I am not sure of the syntax and I can't find anything on google. Would anyone be able to help me out please ?

Thanks a lot.

what's wrong with "knownPrimes[] = {2,3,5,7,9...};"?

user497849
– user497849

2010-12-02 16:44:36 +00:00
Commented Dec 2, 2010 at 16:44 — user497849
– user497849, Commented Dec 2, 2010 at 16:44
@Dorin, need an "int" at the start. or add "new int[]"

Peter Lawrey
– Peter Lawrey

2010-12-02 16:47:37 +00:00
Commented Dec 2, 2010 at 16:47 — Peter Lawrey
– Peter Lawrey, Commented Dec 2, 2010 at 16:47

Bozho · Accepted Answer · 2010-12-02 16:48:29Z

5

int[] knownPrimes = new int[] {2, 3, 5, 7, 9};

As Peter mentioned, the new int[] can be omitted.

edited Dec 2, 2010 at 16:48

answered Dec 2, 2010 at 16:42

Bozho

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4 Comments

Peter Lawrey Over a year ago

the "new int[]" is not needed.

Peter Lawrey Over a year ago

Cheers. ;) +1 as this works even if you are not initialising it.

user476033 Over a year ago

...that works if you're not initialising the variable knownPrimes ?! Mind=blown ! Thank you :)

Peter Lawrey Over a year ago

@user476033, yes see the examples in my post.

Peter Lawrey · Accepted Answer · 2010-12-02 16:48:09Z

3

try

int[] knownPrimes = {2,3,5,7,9};

or

int[] knownPrimes;
knownPrimes = new int[] {2,3,5,7,9}

edited Dec 2, 2010 at 16:48

answered Dec 2, 2010 at 16:43

Peter Lawrey

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Comments

rajah9 · Accepted Answer · 2010-12-02 17:35:09Z

I agree with the solutions posted.

A good book is Thinking in Java, by Bruce Eckel. He covers initialization in Chapter 4, "Initialization and Cleanup," and uses Peter's method. You may buy the latest edition or download an older edition for free.

If the list of knownPrimes is not going to be subclassed, you might want to add the keyword final. If it is class variable and you do not want the value to change after the initialization, you might want to add the keyword static. (I suspect that the list of known primes will be the same throughout the execution of the program.) If you want to access the length of the array, use knownPrimes.length.

Oh, and by the way, 9 should not be in the list of knownPrimes.

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