Lesson 21 of 31

6 mins read

Arrays in Java

In Plain English

An array in Java is a container object that holds a fixed number of values of a single uniform type. The length of an array is established when the array is created and cannot be dynamically resized afterwards.

The Mental Model

"An array is like an egg carton with fixed compartments. A 6-egg carton (length 6) holds exactly 6 items of the exact same type (eggs), numbered from spot 0 to 5."

Deep Dive: How It Works

Declaration with size allocation: `int[] numbers = new int[5];` (allocates 5 integers initialized to 0).

Declaration with literal values: `String[] fruits = {"Apple", "Banana", "Orange"};`

Default values: Numeric arrays initialize to 0/0.0, boolean arrays to false, and object/String arrays to null.

Syntax Blueprint

int[] scores = new int[3];
String[] names = {"Alice", "Bob", "Charlie"};

Square brackets [] declare an array type. Array size is fixed upon instantiation.

Core Rules to Remember

Fixed Capacity: Array size cannot change after creation.

Homogeneous Type: All elements must match the declared data type.

Array Literal Syntax: Use curly braces { item1, item2 } for quick initialization.

Common Beginner Traps & How to Fix Them

Mistake:Putting array size in type declaration: int[5] arr = new int[5];

Why it happens: Java prohibits placing the dimension size on the left side of the assignment.

How to fix: Keep brackets empty on the left: int[] arr = new int[5];

Pro Tip: Prefer int[] numbers over int numbers[]: placing brackets by the type is modern Java style.

Live Interactive Example

Hit Run Code to see it live

Creating and Inspecting Arrays

Java 13

Output Console

Click "Run Code" to view the rendered output.

How it works: Array elements are accessed with [0]. languages.length returns total item count.

Your Turn: Micro Challenge

No pressure! Edit the starter code below and test your solution with instant feedback.

Micro Exercise

Create an array of color names

Declare a String[] named "colors" with {"Red", "Green", "Blue"}.
Print "Second color: " + colors[1].

Sandbox Output

Click "Run & Check" to test your solution.

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