Question

An array A that is already declared as int[] A can be constructed or instantiated as a. \(\mathrm{A}=\) new int \([10]\); b. \(\mathrm{A}=\) new \(\mathrm{A}[10]\); c. Either \(\mathrm{A}\) or \(\mathrm{B}\) d. Both \(\mathrm{A}\) and \(\mathrm{B}\)

Short answer

Option a: `A = new int[10];` is correct.

Step-by-step solution

- Understand the array declaration

The problem states that an array A is declared as `int[] A`. This means `A` is an integer array.

- Examine option a

Option a is `A = new int[10];` which is the correct syntax to instantiate an integer array of size 10.

- Examine option b

Option b is `A = new A[10];` which is incorrect because `A` is not a valid type in this context. The correct type should be `int` for an integer array.

- Analyze options c and d

Option c states that either (a) or (b) can be used. This is incorrect because only option (a) is valid. Option d states that both (a) and (b) can be used, which is also incorrect.

- Final conclusion

Based on the analysis, the only correct way to instantiate the array is given by option a.

Key concepts

Java syntax

When programming in Java, syntax refers to the rules that define how to write instructions for the computer to execute. This includes the structure of statements and expressions, the use of keywords, and punctuation. Java syntax is strict, meaning every statement must adhere to its rules, otherwise, an error will be generated.

For instance, case sensitivity is crucial in Java. A variable named `myArray` is different from `MyArray`. Every statement must end with a semicolon (`;`). Also, Java uses curly braces `{}` to define the scope of loops, methods, and classes.

Understanding Java syntax is critical because it allows you to write code correctly and helps you debug more effectively. Knowing how to properly declare variables, write methods, and structure your code according to Java's rules is essential to becoming proficient in the language.

Array Declaration

Declaring an array in Java is the process of defining an array and specifying its type. The type determines what kind of elements the array will hold. For example, `int[]` means the array will hold integers.

Here's a basic syntax for array declaration:
```java
int[] myArray;
```
This line of code declares an array named `myArray` that will store integers. At this point, the array is only declared, not instantiated. It does not yet have a memory allocated to store any integers. The declaration merely informs the compiler that `myArray` is an array that can store integer-type elements.

An important point to note is the placement of the square brackets `[]`. These brackets can be placed after the type or after the variable name, like this:
```java
int myArray[];
```
Both forms are valid in Java, but the first form (type followed by brackets) is more commonly used and preferred in professional codebases.

Array Instantiation

Instantiation is the process of allocating memory for the array elements. After declaring an array, you need to instantiate it to actually use it in your programs. In the original exercise, this was the main point of confusion.

To instantiate an array in Java, you use the `new` keyword followed by the type and the number of elements the array will hold in square brackets. Here's the syntax:
```java
myArray = new int[10];
```
This line of code creates an array that can hold 10 integers. The `10` inside the brackets specifies the size of the array.

It is crucial to match the type of the array during instantiation. For example, if the array is declared as `int[] myArray`, it must be instantiated as `new int[size]`. Attempting to use an incorrect type, such as `new A[10]`, will result in a compile-time error.

So, in the original exercise, only option `a` (`A = new int[10];`) is the correct way to instantiate an array. This aligns the declaration and the instantiation with the correct type and allocates memory for 10 integer elements.