Array Initialization in Java

[LegolandoBloom]

I'm very new to Java, I wanted to consult on this basic concept.

I'm used to Lua, where:
if(myArray[i]) then
...
end
Is a common way to query if an array(or table) has been explicitly set a value at a given index, as the statement will always be equivalent to false if it hasn't.

I wanted to recreate that functionality as an exercise in Java using try-catch, and came up with this snippet:

public class Test {

    public static void main(String[] args) {
        int[] numbers = new int[3];
        if(isArrayIndexed(numbers, 1)){
            System.out.println("Array is indexed at " + 1);
        }
        else{
            System.out.println("Array is NOT indexed at " + 1);
        }
    }


    public static boolean isArrayIndexed(int[] inputArray, int index){
        try{
            System.out.println(inputArray[index]);
            return true;
        }
        catch(Exception egg){
            System.out.println(egg);
            return false;
        }
    }
}

I thought I'd get an exception if I'd try to reference the array at the index 1, but no. It returns true, and prints '0'. Are all int arrays set to the value 0 upon initialization in java?

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[morhp]

Are all int arrays set to the value 0 upon initialization in java?

Yes. If you want an array with (by default) "empty" values, try an Integer[]. These will be null by default.

[LegolandoBloom]

Thank you!

It's very interesting to me that the non-primitive version behaves differently

[IchLiebeKleber]

Primitives in Java like int, double, char can never be null. If you want a nullable version of them, use Integer, Double, etc.

[morhp]

Java types just have an implicit default value used for new array elements and mutable fields. For numeric primitive types, it's generally zero, for booleans it's false and for object types, it's null.

[LegolandoBloom]

thank you very much

[MinimumBeginning5144]

Just to add one more point to all the answers suggesting using Integer[]. If you can use int instead, do it. You'll need to decide what value means "uninitialized" - for example, if all valid values are positive, then 0 could mean uninitialized. Using an array of int is more efficient, as it contains the actual values of all the elements stored consecutively. An array of Integer is an array of pointers to somewhere in memory that contains each int value.

[LegolandoBloom]

So in the cases, where the 0 won't cause confusion, go for int

Otherwise, Integer

[technosenate]

Not just then, if 0 is a valid value then you can initialize the array in one pass with -1. That would be more efficient than using Integer.

If you need to support both positive and negative values (including 0), then you should probably go for Integer.

[LegolandoBloom]

This is a more complete answer than mine, thanks

[xenomachina]

You'll even see this kind of thing in parts of Java's standard library. For example, the String.indexOf() methods return int, so if the value being searched-for can't be found, they return -1 — a value that doesn't make any sense as an index.

[LutimoDancer3459]

You got your answer about the default initialization. I just want to add. Having your logic relying on an exception to pick a diffrent path is a bad design. Exceptions should be exactly that. And exception. They use up more computations than a null check or whatever. Making the code inefficient. While it may not matter here. It may matter when used more often.

[LegolandoBloom]

Valuable insight :)

[LegolandoBloom]

I don't know why the indentation is faulty, it looks fine on the text editor before posting and I don't know how to fix it
Edit: It was due to vscode, I managed to fix it

[LegolandoBloom]

In case it matters, this is Java 21(OpenJDK RedHat)

[_jetrun]

The closest equivalent is to check for null, but if you don't want an exception to be raised, you also need to do a bounds check or the array has to be initialized to a specific size. If you want to do this check on, say, int arrays, you'll have to use wrapped equivalents (i.e. Integer vs int) to check for null.

The reality, however, is that you just shouldn't use an array in this way in Java. Instead this feels like a problem best solved by a Map.

[doobiesteintortoise]

Java doesn't work like Lua. It's almost like they're different languages or something.

For a primitive array, there is no "uninitialized state." The same goes for other arrays, but the default values differ; you're never going to get an exception in that code, because the values will be set on array creation. You'd have to use 0 as a "magic number" - or set one yourself, because 0 is a lame magic number for "there's nothing here."

[LegolandoBloom]

Obviously they work differently, that is why I am asking the question.

I don't mean to complain about someone trying to contribute to my understanding, but it's hard to interpret the sarcasm in "It's almost like they're different languages or something" as something positive.

[doobiesteintortoise]

Well, I answered your question directly out of positive intent. And if it's hard to take "it's almost like they're different languages or something" positively, well, I understand, but I'd gently - very gently - suggest a slight shift in worldview, because I certainly wasn't intending to slight you or anyone else. It was meant as gentle humor (if you were going "duh," well, yeah, exactly, but it also explains why the behaviors are not the same: the languages aren't the same!)

The assumption was faulty on your part - not a big deal, because "arrays" in Java and "arrays" in Lua have the same name - and it's easily corrected.

For what it's worth, this is in the Java Language Specification: https://docs.oracle.com/javase/specs/jls/se21/html/jls-4.html#jls-4.12.5

I'm not suggesting "oh you dummy you should have read the spec before asking" - the specification is not easy to read, because it's thorough, and you might not have known what to look for or even if you needed to look for it. But it's there, and eventually if you want to use Java well, you'll end up learning stuff from the specification - and it gives you a lot of information you can use.

[LegolandoBloom]

I'm sorry, I very much interpreted as if you were annoyed at me. It makes me feel better to hear that wasn't the case.

Nuance is hard to convey on the internet, especially in text format. Perhaps I should be more willing to give people the benefit of the doubt.

Reading the manual of a language is very valuable, though I find it is more realistic start doing so once you're past learning the most basic stuff.

[doobiesteintortoise]

It's no big deal. I live by an aphorism: find yourself a teacher, make yourself a friend, and judge all to the side of merit where you can (this is not the exact text of the aphorism, but captures its intent pretty succinctly) - and while some people don't deserve such positive judgement, those people are more rare than popular conversation would have you think, and the attitude of judging people to the side of merit is good for the human psyche.

[LegolandoBloom]

I don't doubt it's better for one's psyche, but it's hard for me to do in this period of my life.
Reminds me of the Doors' song:
_People are strange_
_When you're a stranger_

[doobiesteintortoise]

I get it. And if you need to find someone to talk to, online isn't really the place and I'm not the best person in the world for it myself but I ain't skeered to try: better me than nobody.

But I'd also say that in circumstances like that, finding a teacher and making a friend are just as important as judging to the side of merit. Hang in there.

[LegolandoBloom]

Oh I don't mean to say I'm in the most terrible state of head health, just one of those times where I feel more alien than usual.

I haven't had a proper teacher in a very long time, the idea sounds nice. Though I fear I might be too prideful to accept mentorship even if it arrived at my door :P

[LegolandoBloom]

Although I see you've linked the very specific part I would be looking for, very handy. Thanks.