Enhance docs, add more tests in SwapAdjacentBits (#5861)

src/main/java/com/thealgorithms/bitmanipulation/SwapAdjacentBits.java

@@ -1,14 +1,45 @@
 package com.thealgorithms.bitmanipulation;
 
 /**
- * Swap every pair of adjacent bits of a given number.
- * @author Lakshyajeet Singh Goyal (https://github.com/DarkMatter-999)
+ * A utility class to swap every pair of adjacent bits in a given integer.
+ * This operation shifts the even-positioned bits to odd positions and vice versa.
+ *
+ * Example:
+ * - Input: 2 (binary: `10`) → Output: 1 (binary: `01`)
+ * - Input: 43 (binary: `101011`) → Output: 23 (binary: `010111`)
+ *
+ * **Explanation of the Algorithm:**
+ * 1. Mask even-positioned bits: Using `0xAAAAAAAA` (binary: `101010...`),
+ *    which selects bits in even positions.
+ * 2. Mask odd-positioned bits: Using `0x55555555` (binary: `010101...`),
+ *    which selects bits in odd positions.
+ * 3. Shift bits:
+ *    - Right-shift even-positioned bits by 1 to move them to odd positions.
+ *    - Left-shift odd-positioned bits by 1 to move them to even positions.
+ * 4. Combine both shifted results using bitwise OR (`|`) to produce the final result.
+ *
+ * Use Case: This algorithm can be useful in applications involving low-level bit manipulation,
+ * such as encoding, data compression, or cryptographic transformations.
+ *
+ * Time Complexity: O(1) (constant time, since operations are bitwise).
+ *
+ * Author: Lakshyajeet Singh Goyal (https://github.com/DarkMatter-999)
  */
-
 public final class SwapAdjacentBits {
     private SwapAdjacentBits() {
     }
 
+    /**
+     * Swaps every pair of adjacent bits of a given integer.
+     * Steps:
+     * 1. Mask the even-positioned bits.
+     * 2. Mask the odd-positioned bits.
+     * 3. Shift the even bits to the right and the odd bits to the left.
+     * 4. Combine the shifted bits.
+     *
+     * @param num the integer whose bits are to be swapped
+     * @return the integer after swapping every pair of adjacent bits
+     */
     public static int swapAdjacentBits(int num) {
         // mask the even bits (0xAAAAAAAA => 10101010...)
         int evenBits = num & 0xAAAAAAAA;