Java Arrays sort

Java Arrays.sort() Example: Sort a Char Array with Output

Sorting a char array in Java is a one-liner. You call Arrays.sort() and the array is sorted in place. The code below does exactly that, then prints each character on its own line.

The code

import java.util.Arrays;

public class Hello {

    public static void main(String[] args) {

        char k[] = {'c', 'a', 's', 'r'};
        Arrays.sort(k);

        for (int i = 0; i < k.length; i++) {
            System.out.println(k[i]);
        }

    }

}

What is happening here, line by line

• import java.util.Arrays; — Brings in the Arrays utility class. It is in the java.util package.
• char k[] = {'c', 'a', 's', 'r'}; — Declares and initializes a char array with four characters. The order is c, a, s, r.
• Arrays.sort(k); — Sorts the array in place. No new array is created. The original array k is now sorted in ascending order.
• for (int i = 0; i < k.length; i++) — Standard loop from index 0 to the last index.
• System.out.println(k[i]); — Prints each character on its own line.

Output

a
c
r
s

The array started as {'c', 'a', 's', 'r'}. After sorting, it becomes {'a', 'c', 'r', 's'}. The loop prints each one, so you see a, c, r, s on separate lines.

Common mistakes and how to fix them

Mistake	What happens	Fix
Forgetting to import java.util.Arrays	Compile error: "cannot find symbol Arrays"	Add import java.util.Arrays; at the top of the file.
Calling Arrays.sort(k) but ignoring the result	No error. But if you expected a return value, you get nothing. Arrays.sort() returns void.	Remember: the array is sorted in place. Do not assign the result.
Using char[] k = new char[4] without filling it	Sorts the default '\u0000' characters. Output is invisible or blank.	Always initialize the array with values before sorting.
Loop condition i <= k.length	ArrayIndexOutOfBoundsException	Use i < k.length, not <=.

Sorting in descending order

Arrays.sort() only sorts ascending for primitive types like char. To get descending order, sort ascending and then reverse the array manually:

Arrays.sort(k);

for (int i = 0, j = k.length - 1; i < j; i++, j--) {
    char temp = k[i];
    k[i] = k[j];
    k[j] = temp;
}

After this, the array will be {'s', 'r', 'c', 'a'}, and the loop prints each character in descending order.

Where to go next

You now know how to sort a char array in Java, how Arrays.sort() works in place, and the mistakes that break the loop.

If you remember one thing, remember this: Arrays.sort() sorts the array in place. It returns nothing. You do not reassign the result.

If you want to go deeper, try these next steps:

• Sort an int[] and a String[] with the same method. Notice that it works the same way for all primitive types and Comparable objects.
• Sort a String[] in reverse order using Arrays.sort(arr, Collections.reverseOrder()). This only works for object arrays, not primitive arrays.
• Compare Arrays.sort() with Collections.sort(). The first is for arrays, the second is for lists.
• Explore the two-pointer trick used above for reversing. It is the same pattern used in many array problems in coding interviews.