🔢 Java: How to Sort an Array (Ascending & Descending)

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🧲 Introduction – Why Sorting Arrays Matters

Sorting is one of the most frequent and critical operations in programming. Whether you’re organizing search results, ranking scores, or optimizing data analysis, sorting arrays is a must-have skill.

✅ In this guide, you’ll learn:

• How to sort integer, string, and custom arrays in Java
• Sort in ascending and descending order
• Use of Arrays.sort() and Collections.reverseOrder()
• Best practices for performance and correctness

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📚 Required Import

import java.util.Arrays;
import java.util.Collections;

✅ Explanation:

• Arrays.sort() is used for sorting arrays.
• Collections.reverseOrder() is used to sort arrays in descending order (only for object arrays).

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🔼 Method 1: Sort an Integer Array in Ascending Order

import java.util.Arrays;

public class SortIntAsc {
    public static void main(String[] args) {
        int[] numbers = {50, 10, 30, 20, 40};
        Arrays.sort(numbers);

        System.out.println("Sorted Array (Ascending): " + Arrays.toString(numbers));
    }
}

✅ Explanation:

• Arrays.sort() arranges elements in ascending order.
• Works with primitive types like int, char, etc.

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🔽 Method 2: Sort Integer Array in Descending Order

import java.util.Arrays;
import java.util.Collections;

public class SortIntDesc {
    public static void main(String[] args) {
        Integer[] numbers = {50, 10, 30, 20, 40};
        Arrays.sort(numbers, Collections.reverseOrder());

        System.out.println("Sorted Array (Descending): " + Arrays.toString(numbers));
    }
}

✅ Explanation:

• You must use Integer[] instead of int[] because Collections.reverseOrder() works with objects, not primitives.

💡 Tip: Use Integer[] if you need reverse sorting.

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🔤 Method 3: Sort a String Array Alphabetically

import java.util.Arrays;

public class SortStrings {
    public static void main(String[] args) {
        String[] names = {"Zara", "Mike", "Alex", "Bob"};
        Arrays.sort(names);

        System.out.println("Sorted Names: " + Arrays.toString(names));
    }
}

✅ Explanation:

• Arrays.sort() uses lexicographical order (A-Z).

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🔁 Method 4: Sort a String Array in Reverse Order

import java.util.Arrays;
import java.util.Collections;

public class SortStringsDesc {
    public static void main(String[] args) {
        String[] names = {"Zara", "Mike", "Alex", "Bob"};
        Arrays.sort(names, Collections.reverseOrder());

        System.out.println("Sorted Names (Descending): " + Arrays.toString(names));
    }
}

✅ Explanation:

• Reverse alphabetical sorting using Collections.reverseOrder().

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🔧 Method 5: Sort Part of an Array

int[] partial = {10, 5, 30, 25, 40, 35};
Arrays.sort(partial, 1, 5);  // Sorts elements from index 1 to 4

✅ Explanation:

• Only sorts elements from index 1 (inclusive) to 5 (exclusive).

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📊 Performance Note

Array Type	Method	Sort Time Complexity
int[], double[]	Arrays.sort()	O(n log n)
Integer[], String[]	Arrays.sort()	O(n log n) (uses TimSort)

💡 Note: For large-scale data, consider parallelSort() introduced in Java 8.

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💡 Best Practices

• ✅ Use Arrays.sort() for quick and clean sorting
• ✅ Use Collections.reverseOrder() only with object arrays
• ⚠️ Avoid converting int[] to Integer[] unless necessary
• ✅ Use Arrays.toString() to print arrays cleanly

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📌 Summary – Sorting Arrays in Java

Sorting is a core Java skill used in virtually every application domain. With Arrays.sort() and helper classes, Java makes it easy to sort data quickly and efficiently.

🧾 Key Takeaways:

• Use Arrays.sort() for most sorting needs.
• Use Collections.reverseOrder() for descending sort (object arrays).
• Use Arrays.toString() to print sorted arrays.
• Optimize performance by avoiding unnecessary boxing/unboxing.

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❓FAQs – Sort an Array in Java

❓ How to sort an array in Java?

Use Arrays.sort(array) for ascending order.

❓ How to sort an array in descending order?

Convert to Integer[] or String[], then use:

Arrays.sort(array, Collections.reverseOrder());

❓ Can I sort only part of an array?

Yes, use Arrays.sort(array, fromIndex, toIndex).

❓ What’s the difference between int[] and Integer[]?

int[] is primitive and doesn’t support object-based operations like reverse sorting.

❓ Is sorting stable in Java?

Yes, for object arrays Java uses TimSort, which is stable.

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