Creation of Array

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1. Introduction

After understanding the basics of arrays, the next step is learning how to create arrays in Java.
Array creation involves:

1. Declaring an array
2. Allocating memory for it using new
3. Optionally initializing it with values

Java arrays are objects, and memory allocation happens at runtime.

2. Array Creation Process

Array creation has two steps:

Step 1: Array Declaration

int[] numbers;

This tells Java:

• numbers is a variable
• It will refer to an array of integers
• No memory is allocated yet

Step 2: Array Memory Allocation

numbers = new int[5];

This creates space for 5 integers in memory.

You can combine both steps:

int[] numbers = new int[5];

3. Syntax of Array Creation

dataType[] arrayName = new dataType[size];

Examples:

int[] marks = new int[4];
double[] temperature = new double[10];
char[] vowels = new char[5];
String[] names = new String[3];

4. Default Values After Creation

When an array is created with new, Java initializes all elements with default values:

Example:

boolean[] flags = new boolean[3];

System.out.println(flags[0]); // false
System.out.println(flags[1]); // false
System.out.println(flags[2]); // false

5. Creating Arrays with Initial Values (Array Literals)

You can create an array and assign values immediately:

Method 1: Direct Literal

int[] nums = {10, 20, 30};

Java counts elements and sets the array size automatically.

Method 2: Using new

int[] nums = new int[] {10, 20, 30};

Both are valid.

6. Creating Arrays Without Initialization

If values are not known initially:

int[] values = new int[5];

// Assign values later
values[0] = 100;
values[1] = 200;

7. Different Ways to Declare and Create Arrays

Way 1: Common Approach

int[] a = new int[3];

Way 2: Alternate Syntax

int a[] = new int[3];

Both work, but the first style is recommended because it clearly shows the variable is an array.

Way 3: 2D Array Creation (Preview)

int[][] matrix = new int[3][4];

(This is covered fully in multi-dimensional-array.mdx)

8. Errors During Array Creation

8.1 Negative Array Size

int[] arr = new int[-5]; // Runtime Error: NegativeArraySizeException

8.2 Missing Size When Using new

int[] arr = new int[]; // ERROR

8.3 Declaring Without Creating Memory

int[] arr;
arr[0] = 10; // NullPointerException

9. Best Practices

• Always use int[] a style for clarity.
• Use array literals when values are known beforehand.
• Use new when size is known but values are not.
• Avoid excessively large arrays → may cause OutOfMemoryError.
• Use meaningful variable names:

Bad:

int[] x = new int[10];

Good:

int[] studentMarks = new int[10];

10. Complete Example

public class ArrayCreation {
    public static void main(String[] args) {

        // Creating array of size 4
        int[] marks = new int[4];

        // Assigning values
        marks[0] = 85;
        marks[1] = 90;
        marks[2] = 78;
        marks[3] = 88;

        // Printing values
        for (int i = 0; i < marks.length; i++) {
            System.out.println("marks[" + i + "] = " + marks[i]);
        }
    }
}

Output:

marks[0] = 85
marks[1] = 90
marks[2] = 78
marks[3] = 88

11. Summary

• Arrays are created using new or array literals.
• Array size is fixed once created.
• Default values are automatically assigned.
• Access elements using index; index starts at 0.
• Proper array creation prevents NullPointerException and other errors.

Written By: Shiva Srivastava