Question

Write a code segment that declares a variable to reference an array of integers with 10 rows and 20 columns and assigns this variable a new array object.

Short answer

int[][] variableName = new int[10][20];

Step-by-step solution

Declaration

Declare a variable to reference a two-dimensional array of integers. This involves specifying the data type and the dimensions of the array. In Java, this can be done using the syntax: `int[][] variableName;`.

Instantiate the Array

Assign the declared variable a new array object that has 10 rows and 20 columns. This is done using the `new` keyword, followed by the data type and the specified dimensions. For example: `variableName = new int[10][20];`.

Combine Declaration and Instantiation (Optional)

Alternatively, combine the declaration and instantiation in a single statement. This makes the code more concise: `int[][] variableName = new int[10][20];`.

Key concepts

array declaration

In Java, declaring an array is the first step before you can use it. An array declaration involves specifying the array's data type and dimensions. For a two-dimensional array of integers, you use the syntax: `int[][] arrayName;`.
This tells Java that `arrayName` will reference a 2D array of integers.
Remember, this step only sets up the array's reference; it doesn't actually create the array itself. We will do that in the next step, array instantiation.

array instantiation

Once you've declared your array, the next step is to instantiate it. Instantiation is the process of actually creating the array object in memory.
To instantiate a 2D array with 10 rows and 20 columns, you use the `new` keyword followed by the data type and the desired dimensions: `arrayName = new int[10][20];`.
At this point, the array `arrayName` is created with 10 rows and 20 columns, and all its elements are initialized to zero (the default value for `int` type).
Instantiation is crucial because without it, the array reference you've declared would point to nothing, and trying to use it would cause your program to crash.

Java syntax

Java syntax is quite structured and simple once you understand the basics. When working with arrays, understanding Java's syntax will save you time and help avoid errors.

To declare and instantiate a 2D array in one line, you combine both steps: `int[][] arrayName = new int[10][20];`. This line does two things:

• Declares `arrayName` as a reference to a 2D array of integers.
• Instantiates a new 2D array with 10 rows and 20 columns, initializing all elements to zero.

Java uses curly braces `{}` to denote blocks of code. For arrays, using the proper brackets `[]` is essential to avoid syntax errors. Spacing and indentation are not just for readability; they are good practices that help other developers understand your code too.