Arrays Utility Class

1. Introduction

The Arrays class in Java (from java.util) is a utility/helper class that provides ready-made methods to work with arrays.

Arrays in Java are fixed-size and do not come with rich methods like collections.
So java.util.Arrays gives you powerful operations such as:

• sorting arrays
• searching values
• filling values
• comparing arrays
• converting array to string
• copying arrays
• working with streams

It is one of the most useful classes when working with arrays in real projects and interviews.

2. Why Arrays Utility Class Is Needed

If you work with raw arrays, you often need to write logic manually:

• loop for sorting
• loop for searching
• loop for printing

This is slow and error-prone.

Arrays class solves this by providing tested and optimized implementations.

3. Import and Basic Usage

Arrays is in java.util, so import it:

import java.util.Arrays;

You do not create object of Arrays because its methods are static.

Usage pattern:

Arrays.methodName(array);

4. Printing Arrays: toString() and deepToString()

4.1 toString() for 1D Arrays

int[] a = {10, 20, 30};
System.out.println(Arrays.toString(a));

Output:

[10, 20, 30]

Without Arrays.toString(), printing an array gives memory reference.

4.2 deepToString() for 2D Arrays

int[][] m = {{1, 2}, {3, 4}};
System.out.println(Arrays.deepToString(m));

Output:

[[1, 2], [3, 4]]

5. Sorting Arrays: sort()

Sorts the array in ascending order.

int[] nums = {5, 2, 9, 1};
Arrays.sort(nums);
System.out.println(Arrays.toString(nums));

Output:

[1, 2, 5, 9]

Important:

• Sorting happens in-place (same array gets modified).
• For objects, it uses natural order or comparator (advanced).

6. Searching in Sorted Array: binarySearch()

binarySearch() works only if the array is already sorted.

int[] nums = {1, 2, 5, 9};
int index = Arrays.binarySearch(nums, 5);
System.out.println(index);

Output:

2

If element not found, it returns a negative value.

Common mistake: Using binarySearch on unsorted array gives wrong results.

7. Filling Array: fill()

Sets same value at all positions.

int[] a = new int[5];
Arrays.fill(a, 7);
System.out.println(Arrays.toString(a));

Output:

[7, 7, 7, 7, 7]

Also supports range filling:

int[] b = {1, 2, 3, 4, 5};
Arrays.fill(b, 1, 4, 0);
System.out.println(Arrays.toString(b));

Output:

[1, 0, 0, 0, 5]

Range rule:

• start index inclusive
• end index exclusive

8. Comparing Arrays: equals() and deepEquals()

8.1 equals() for 1D arrays

int[] a = {1, 2, 3};
int[] b = {1, 2, 3};

System.out.println(Arrays.equals(a, b)); // true

== would return false because it checks reference.

8.2 deepEquals() for 2D arrays

int[][] x = {{1, 2}, {3, 4}};
int[][] y = {{1, 2}, {3, 4}};

System.out.println(Arrays.deepEquals(x, y)); // true

9. Copying Arrays: copyOf() and copyOfRange()

9.1 copyOf()

Creates a new array and copies data.

int[] a = {1, 2, 3};
int[] copy = Arrays.copyOf(a, a.length);

System.out.println(Arrays.toString(copy));

9.2 copyOfRange()

Copies part of an array.

int[] a = {10, 20, 30, 40, 50};
int[] part = Arrays.copyOfRange(a, 1, 4);

System.out.println(Arrays.toString(part));

Output:

[20, 30, 40]

10. Converting Array to Stream (Modern Use)

You can create stream from array for advanced operations.

int[] nums = {1, 2, 3, 4};

int sum = Arrays.stream(nums).sum();
System.out.println(sum);

Output:

10

This is useful when combining arrays with Stream API.

11. Summary

• java.util.Arrays is a utility class for array operations.

• Common methods:

  • toString(), deepToString()
  • sort()
  • binarySearch() (requires sorted array)
  • fill()
  • equals(), deepEquals()
  • copyOf(), copyOfRange()
  • stream()

• It reduces manual loops and provides efficient implementations.

Written By: Shiva Srivastava