Arrays in Java – Declaration, Initialization and Examples

Q: How do I find the length of an array?

Use the length field (no parentheses): arr.length.

Q: What are the default values of array elements?

0 for numeric types, '\u0000' for char, false for boolean and null for reference types.

Q: How do I print an array?

Use Arrays.toString(arr) for one-dimensional arrays and Arrays.deepToString(arr) for multidimensional arrays.

Q: How do I copy an array?

Use arr.clone(), Arrays.copyOf(arr, arr.length) or System.arraycopy(). Plain assignment only copies the reference.

Q: How do I compare two arrays?

Use Arrays.equals(a, b) for content equality, or Arrays.deepEquals() for nested arrays. == only checks whether they are the same object.

Last updated: October 11, 2026Oct 11, 2026 7 min read

An array stores a fixed number of values of the same type in one variable. Instead of declaring mark1, mark2 … mark50, you create one array of 50 marks and reach each one by its position, called its index.

Arrays are the most basic data structure in Java and the foundation of many others, including ArrayList. This tutorial covers declaring, creating and initialising arrays, reading and writing elements, default values, looping, the Arrays helper class, and common pitfalls.

1. What Is an Array?

Think of an array as a row of numbered lockers. All lockers are the same size (same type), the row has a fixed length, and each locker is opened by its number, starting from 0.

Same type: an int[] holds only int values; a String[] holds only strings.
Fixed size: the length is set when the array is created and never changes.
Zero-based indexes: the first element is at index 0, the last at length - 1.
Fast access: reading or writing any element by index takes constant time.
Arrays are objects: they live on the heap, have a length field and can be null.

2. Declaring, Creating and Initialising

Ways to create an array

int[] a;                          // declaration only (a is not created yet)
a = new int[5];                   // creation: 5 elements, all 0

int[] b = new int[5];             // declaration + creation
int[] c = {10, 20, 30};           // declaration + initialisation (size 3)
int[] d = new int[] {10, 20, 30}; // same, also usable outside a declaration
int e[] = new int[3];             // C-style brackets are legal but discouraged

ArrayBasics.java

public class ArrayBasics {
    public static void main(String[] args) {
        // 1. Declare and create: 5 slots, all set to the default value 0
        int[] marks = new int[5];

        // 2. Assign values by index (0 to length - 1)
        marks[0] = 78;
        marks[1] = 92;
        marks[2] = 65;
        marks[3] = 88;
        marks[4] = 71;

        // 3. Read values
        System.out.println("First mark: " + marks[0]);
        System.out.println("Last mark:  " + marks[marks.length - 1]);
        System.out.println("Length:     " + marks.length);

        // Declare, create and initialise in one step
        String[] days = {"Mon", "Tue", "Wed"};
        for (String d : days) System.out.print(d + " ");
        System.out.println();
    }
}

Output

First mark: 78
Last mark:  71
Length:     5
Mon Tue Wed

3. Default Values and Printing

When an array is created with new, every element gets the default value of its type. To print an array's contents, use Arrays.toString(); printing the array directly shows only its type and a hash code.

ArrayDefaults.java

import java.util.Arrays;

public class ArrayDefaults {
    public static void main(String[] args) {
        System.out.println("int[]:     " + Arrays.toString(new int[3]));
        System.out.println("double[]:  " + Arrays.toString(new double[3]));
        System.out.println("boolean[]: " + Arrays.toString(new boolean[3]));
        System.out.println("char[]:    " + Arrays.toString(new char[3]).replace('\u0000', '0') + "  (the \\u0000 character)");
        System.out.println("String[]:  " + Arrays.toString(new String[3]));

        int[] data = {1, 2, 3};
        System.out.println("println(array) prints: " + (data.toString().startsWith("[I@") ? "[I@... (type and hash code)" : data));
        System.out.println("Arrays.toString:       " + Arrays.toString(data));
    }
}

Output

int[]:     [0, 0, 0]
double[]:  [0.0, 0.0, 0.0]
boolean[]: [false, false, false]
char[]:    [0, 0, 0]  (the \u0000 character)
String[]:  [null, null, null]
println(array) prints: [I@... (type and hash code)
Arrays.toString:       [1, 2, 3]

4. Looping Over Arrays

Use a classic for loop when you need the index, and a for-each loop when you only need the values:

Two ways to loop

for (int i = 0; i < marks.length; i++) {
    System.out.println("Student " + (i + 1) + ": " + marks[i]);
}

for (int m : marks) {
    System.out.println(m);
}

5. Common Operations and the Arrays Class

The java.util.Arrays class provides ready-made helpers for sorting, searching, copying, filling and comparing arrays:

ArrayOperations.java

import java.util.Arrays;

public class ArrayOperations {
    public static void main(String[] args) {
        int[] scores = {72, 95, 58, 81, 64};

        int sum = 0, max = scores[0];
        for (int s : scores) {
            sum += s;
            if (s > max) max = s;
        }
        System.out.println("sum = " + sum + ", average = " + (double) sum / scores.length + ", max = " + max);

        int[] sorted = scores.clone();          // copy before sorting
        Arrays.sort(sorted);
        System.out.println("sorted:   " + Arrays.toString(sorted));
        System.out.println("original: " + Arrays.toString(scores));
        System.out.println("index of 81 in sorted: " + Arrays.binarySearch(sorted, 81));

        int[] bigger = Arrays.copyOf(scores, 7);   // resize by copying
        System.out.println("copyOf to 7: " + Arrays.toString(bigger));

        int[] filled = new int[4];
        Arrays.fill(filled, 9);
        System.out.println("fill(9): " + Arrays.toString(filled));
        System.out.println("equals: " + Arrays.equals(scores, scores.clone()));
        System.out.println("stream sum: " + Arrays.stream(scores).sum());
    }
}

Output

sum = 370, average = 74.0, max = 95
sorted:   [58, 64, 72, 81, 95]
original: [72, 95, 58, 81, 64]
index of 81 in sorted: 3
copyOf to 7: [72, 95, 58, 81, 64, 0, 0]
fill(9): [9, 9, 9, 9]
equals: true
stream sum: 370

Method	Purpose
`Arrays.toString(a)`	Readable text of the elements.
`Arrays.sort(a)`	Sorts in ascending order (in place).
`Arrays.binarySearch(a, key)`	Finds a value in a sorted array.
`Arrays.copyOf(a, n)`, `copyOfRange`	Copies into a new array of another size.
`Arrays.fill(a, v)`	Sets every element to `v`.
`Arrays.equals(a, b)`	Compares contents.
`Arrays.stream(a)`	Processes elements with streams.
`Arrays.asList(...)`	Fixed-size list view of an object array.

See Arrays class in Java for more.

6. Common Pitfalls

ArrayPitfalls.java

import java.util.Arrays;

public class ArrayPitfalls {
    public static void main(String[] args) {
        int[] nums = {10, 20, 30};

        // Index out of range
        try {
            System.out.println(nums[3]);
        } catch (ArrayIndexOutOfBoundsException e) {
            System.out.println("Error: " + e.getMessage());
        }

        // Arrays are objects: assignment copies the reference
        int[] alias = nums;
        alias[0] = 99;
        System.out.println("nums after changing alias: " + Arrays.toString(nums));

        // == compares references, Arrays.equals compares contents
        int[] same = {99, 20, 30};
        System.out.println("nums == same: " + (nums == same) + ", Arrays.equals: " + Arrays.equals(nums, same));

        // The size is fixed after creation
        System.out.println("length stays " + nums.length + "; use ArrayList for a growable list");
    }
}

Output

Error: Index 3 out of bounds for length 3
nums after changing alias: [99, 20, 30]
nums == same: false, Arrays.equals: true
length stays 3; use ArrayList for a growable list

Accessing index length or a negative index throws ArrayIndexOutOfBoundsException.
Assigning one array variable to another copies the reference; use clone() or Arrays.copyOf() for a real copy.
== compares references; use Arrays.equals() to compare contents.
Arrays cannot grow; use an ArrayList when the size changes.
Arrays use the field length; strings use the method length(); collections use size().

7. Types of Arrays

Single-dimensional arrays: a simple list of values.
Multidimensional arrays: arrays of arrays, such as tables and matrices.
Jagged arrays: 2D arrays whose rows have different lengths.
Anonymous arrays: arrays created without a variable name.

8. Array vs ArrayList

Feature	Array	ArrayList
Size	Fixed	Grows automatically
Primitives	Yes (`int[]`)	No, uses wrappers (`Integer`)
Length	`arr.length`	`list.size()`
Methods	Through the `Arrays` class	Built in (`add`, `remove`, `contains`…)
Performance and memory	Slightly better	Slight overhead

9. Summary

An array holds a fixed number of elements of one type, accessed by indexes from 0 to length - 1.
Create arrays with new type[size] or an initializer {...}; new elements get default values.
Arrays are objects: assignment copies references, and == compares references.
The Arrays class sorts, searches, copies, fills, compares and prints arrays.
Use an ArrayList when you need a size that can change.

Frequently Asked Questions (FAQ)

Q1. What is an array in Java?

An object that holds a fixed number of values of the same type, stored in order and accessed by a zero-based index.

Q2. Why do Java array indexes start at 0?

The index is the offset from the start of the array. The first element is at offset 0. This convention comes from C and makes address calculation simple.

Q3. How do I find the length of an array?

Use the length field (no parentheses): arr.length.

Q4. Can I change the size of an array?

No. The size is fixed at creation. To "resize", create a new array with Arrays.copyOf(), or use an ArrayList.

Q5. What are the default values of array elements?

0 for numeric types, '\u0000' for char, false for boolean and null for reference types.

Q6. What is ArrayIndexOutOfBoundsException?

The exception thrown when you access an index below 0 or greater than or equal to the array's length.

Q7. How do I print an array?

Use Arrays.toString(arr) for one-dimensional arrays and Arrays.deepToString(arr) for multidimensional arrays.

Q8. Are arrays objects in Java?

Yes. Even arrays of primitives are objects on the heap, with a length field and the methods of Object.

Q9. How do I copy an array?

Use arr.clone(), Arrays.copyOf(arr, arr.length) or System.arraycopy(). Plain assignment only copies the reference.

Q10. How do I compare two arrays?

Use Arrays.equals(a, b) for content equality, or Arrays.deepEquals() for nested arrays. == only checks whether they are the same object.

Q11. How do I sort an array?

Arrays.sort(arr) sorts in ascending order. For object arrays, pass a Comparator, such as Arrays.sort(names, Comparator.reverseOrder()).

Q12. Can an array hold different types?

Only through a common supertype, for example an Object[] can hold strings and integers. In practice, arrays usually hold one specific type.

Q13. What is the difference between int[] a and int a[]?

None for a single variable; both declare an int array. int[] a is the preferred Java style because it keeps the type together.

Q14. Can an array have length 0?

Yes, new int[0] is a valid empty array. Returning an empty array instead of null spares callers a null check.

Q15. What is the maximum size of an array?

Indexes are int, so the theoretical limit is about 2.1 billion elements; in practice it is limited by available heap memory (and some JVMs reserve a few slots).

Q16. How do I convert an array to a List?

List.of(arr) for an unmodifiable list, Arrays.asList(arr) for a fixed-size view, or new ArrayList<>(Arrays.asList(arr)) for a fully modifiable list (object arrays only).

Q17. How do I find the largest element in an array?

Loop and track the maximum, or use Arrays.stream(arr).max().getAsInt() for an int[].

Q18. Where are arrays stored in memory?

On the heap. A local array variable on the stack holds only a reference to the array object.

Q19. Should I use an array or an ArrayList?

Use an array for fixed-size data and primitives where memory and speed matter. Use an ArrayList when elements are added or removed and you want built-in methods.

Q20. What does arr.clone() return for arrays of objects?

A shallow copy: a new array containing the same object references. The objects themselves are not copied.

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Arrays in Java – Declaration, Initialization and Examples

1. What Is an Array?

2. Declaring, Creating and Initialising

3. Default Values and Printing

4. Looping Over Arrays

5. Common Operations and the Arrays Class

6. Common Pitfalls

7. Types of Arrays

8. Array vs ArrayList

9. Summary

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Frequently Asked Questions (FAQ)