Arrays.copyOf() / Arrays.copyOfRange() / Arrays.fill()

import java.util.Arrays;

// Copies an array and returns a new array of the specified length.
Arrays.copyOf(original, int newLength);

// Copies a specified range and returns a new array.
Arrays.copyOfRange(original, int from, int to);

// Fills the entire array with the specified value (destructive operation).
Arrays.fill(array, value);

// Fills a specified range with the specified value (destructive operation).
Arrays.fill(array, int fromIndex, int toIndex, value);

// Performs a fast array copy.
System.arraycopy(src, int srcPos, dest, int destPos, int length);

import java.util.Arrays;

// Copy an array using Arrays.copyOf().
int[] original = {1, 2, 3, 4, 5};
int[] copy = Arrays.copyOf(original, 3); // Copies the first 3 elements.
System.out.println(Arrays.toString(copy)); // Outputs "[1, 2, 3]".

// Copy with a larger length (extra elements are filled with 0).
int[] extended = Arrays.copyOf(original, 8);
System.out.println(Arrays.toString(extended)); // Outputs "[1, 2, 3, 4, 5, 0, 0, 0]".

// Copy a range using Arrays.copyOfRange().
int[] range = Arrays.copyOfRange(original, 1, 4); // Copies indexes 1 through 3.
System.out.println(Arrays.toString(range)); // Outputs "[2, 3, 4]".

// Fill all elements using Arrays.fill().
int[] filled = new int[5];
Arrays.fill(filled, 7);
System.out.println(Arrays.toString(filled)); // Outputs "[7, 7, 7, 7, 7]".

// Fill a specific range.
int[] partial = {0, 0, 0, 0, 0};
Arrays.fill(partial, 1, 4, 9); // Fills indexes 1 through 3 with 9.
System.out.println(Arrays.toString(partial)); // Outputs "[0, 9, 9, 9, 0]".

// Perform a fast copy using System.arraycopy().
int[] src = {10, 20, 30, 40, 50};
int[] dest = new int[5];
System.arraycopy(src, 1, dest, 0, 3); // Copies elements 1–3 of src to the start of dest.
System.out.println(Arrays.toString(dest)); // Outputs "[20, 30, 40, 0, 0]".

Arrays.copyOf() and Arrays.copyOfRange() return a new array and do not affect the original. You can also use them to resize an array. When copying an array of objects, only the references are copied (shallow copy). Modifying an object through the copy will also affect the original array, so implement a deep copy if you need a fully independent copy.

Arrays.fill() is commonly used to initialize arrays. It is useful whenever you want to set all elements to the same value, such as when initializing a game map or setting up default values.

To sort an array, use Arrays.sort(). To compare or convert arrays to strings, use Arrays.equals() / Arrays.toString().