Correct way of declaring arrays using the Array() constructor?

write statements to declare the array and assign the values to the corresponding positions.
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I know that the Array() constructor takes in two arguments: the size of the array and a function which receives the index of an array and returns the value for that index.

I've written some example programs in the kotlinlang.org online IDE, and have declared & initialised my arrays as such:

var array = Array(9, {i -> ' '})

A "blank" char array of size 9, completely filled with whitespaces. This works fine in the kotlinlang.org compiler, and runs well too; however, when I try to import the same code to IntelliJ-IDEA, I get the following warning:

Warning: Kotlin: Parameter 'i' is never used, could be renamed to _

What does the underscore character mean? How does it act as an index? Renaming i to _ does remove the warning, but what does it do, exactly?

How should I correctly use the Array() constructor to initialise a an array using a lambda expression? Bear in mind, I know that the lambda expression can be written outside the brackets, but I chose to include it anyway because it is pretty simple.

Thanks in advance.

It says "Warning" not "error".

Warning: Kotlin: Parameter 'i' is never used, could be renamed to _

The code is compiling fine, it's just informing you that the unused lambda parameter can be renamed to _ to make it more obvious that the lambda parameter is unused.

So, to answer you question, you have constructed the array correctly. However, if for some reason you wanted to use the index to construct the array, you can leave it named and use it for calculations inside the lambda that is executed for constructing each element of the array. For instance:

val array = Array(10, { i -> i * 10  })

Which would result in an array like:

[0, 10, 20, 30, 40, 50, 60, 70, 80, 90]

Also, something to note, you have used var, this means your variable array is mutable (i.e. the whole variable can be re-assigned). This is probably not what you want, so you should favour val unless you specifically want a mutable variable.

Arrays in Java, A Java array variable can also be declared like other variables with [] after the data type. An array declaration has two components: the type and the name. type The Student objects have to be instantiated using the constructor of the Student The public method clone(), which overrides clone method in class Object and  Arrays we have mentioned till now are called one-dimensional arrays. However, we can declare multidimensional arrays in Java. A multidimensional array is an array of arrays. That is, each element of a multidimensional array is an array itself. For example, double[][] matrix = {{1.2, 4.3, 4.0}, {4.1, -1.1} };

It is just a warning.

In Kotlin if you do not use parameter you can rename it to _. It is more readable. In your case you do not use i on the right side of your lambda function. So you can rename it to _

Correct way of declaring arrays using the Array() constructor , It says "Warning" not "error". Warning: Kotlin: Parameter 'i' is never used, could be renamed to _. The code is compiling fine, it's just informing  Assignment is not initialization to begin with (and it's disallowed for naked C-style arrays). You can initialize (not "declare" as in the question's title) array members the same way you initialize any class members in consructors: [code]#inclu

As other answers have said, your code is correct, but since you're not using the parameter i, there's no need to give it a name.  You can instead use _, which is simply a placeholder: it indicates to Kotlin that the lambda takes a parameter, but you don't care about it.

(The underscore might not seem very useful here, but it can help in more complex cases.  For example, if you had a big Person class with many fields, you could use just a couple of them with e.g. for ((name, _, _, age) in persons)…)

In fact, you can simplify the expression even further!  Unlike more traditional block-structured languages, in Kotlin braces usually indicate a lambda (except in cases such as function bodies, and if and when branches), even without a ->.  And here Kotlin can infer the number as well as the type of parameters.  So you can drop the parameter and arrow entirely, and simply use:

var array = Array(9, {' '})

Chapter 7: Arrays, Declare, Initialize, and Use Arrays; Use Loops for Array Traversal; Pass We need a way to declare many variables in one step and then be able to store and access their values. Assign the value at index right to the element at index left. I know that the Array() constructor takes in two arguments: the size of the array and a function which receives the index of an array and returns the value for that index. I've written some example programs in the kotlinlang.org online IDE, and have declared & initialised my arrays as such: var array = Array(9, {i -> ' '})

All of the definitions below create the same array. Kotlin (and IntelliJ) discourage redundant code, so _ is "better" then i (as i is not used) and "nothing" is better then _. Finally, IntelliJ encourages last parameter lambda to be in a separate block - as per the fourth example:

Array(9, { i -> ' ' })
Array(9, { _ -> ' ' })
Array(9, { ' ' })
Array(9) { ' ' }

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Comments
  • It signals the reader that this argument is never used.
  • I see. This makes perfect sense. Thank you.
  • In that case upvote it and accept it as the answer please