Arrays in Java are quite a broad topic, so as part of our Programming I course, we’re going to create a separate series focused just on arrays. This will include several lectures specifically about working with arrays in Java.

1. What Are Arrays?

An array is a data structure that lets you store a group of elements of the same type. You can think of it like a bookshelf where each book (element in the array) has its own fixed place (called an index).
Arrays are used everywhere — from simple lists of numbers or names to storing coordinates in geometry tasks (like simulating a parking lot or organizing books in a library).

2. How to Create an Array?

To create an array, you need to define its data type, size, and/or initial values.

// Example: creating an array of 5 integers
int[] numbers = new int[5];

• int[] numbers — this is a variable declaration that can refer to an array of integers.
• new int[5] — this is the creation of a new array object (with 5 elements) in memory.
• As a result, the variable numbers will point to the newly created array.

Variables and Arrays in Java: What’s Important to Know
Even though here we’re creating a new object using new int[5];, this part: int[] numbers is actually a variable.
If you find it difficult to understand different Java constructs, here’s a helpful simplification: almost anything in Java that looks like int[] numbers = is basically a variable.

1. Declaring a Variable and an Array
   The expression int[] numbers is a declaration of a variable that can hold a reference to an integer array. You’re specifying the data type (an array of integers) and the name of the variable (numbers).
2. Creating the Array Object
   The part new int[5] creates a new array object in memory, with space for 5 integer values.
3. Linking the Variable and the Array
   When we write int[] numbers = new int[5];, the variable numbers becomes a reference (or link) to the created array object. It’s important to understand that a variable of type int[] is not the array itself — it only points to the array.
4. Easy Comparison
   • The variable is like a label attached to the array.
   • The array is the object that actually stores the data.

3. Initializing an Array

You can also initialize an array right away when you create it:

int[] numbers = {10, 20, 30, 40, 50};

4. Accessing Array Elements

To access an element in the array, use its index. Indexes start at 0:

System.out.println(numbers[0]); // This will print 10

5. Changing Array Elements

You can also change elements by using their index:

numbers[1] = 25; // The second element is now 25

6. Looping Through an Array

You can go through an array using a classic for loop:

for (int i = 0; i < numbers.length; i++) {
    System.out.println(numbers[i]);
}

Or use the improved for-each loop:

for (int number : numbers) {
    System.out.println(number);
}

7. Common Mistakes

1. Going Outside the Array Bounds:
   Trying to access an index that doesn’t exist: System.out.println(numbers[5]); // Error! Index goes only up to 4.
2. Uninitialized Elements:
   By default, numeric array elements are set to 0, and object types (like strings) are set to null.
   If you try to use such values without checking, you may run into errors.

8. Practice Task

1. Create an array with 10 elements filled with the numbers from 1 to 10.
2. Calculate and print the sum of all elements in the array.
3. Find and print the largest number in the array.

Arrays are one of the most important basic data structures for working with groups of information. Being able to create, initialize, modify, and loop through arrays is a key skill for moving on to more advanced algorithms and data structures. Always remember: the array variable and the array object are two separate things — the variable holds a reference, and the object holds the actual data.