Add SwapAdjacentBits.java new algorithm

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

@@ -0,0 +1,26 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * Swap every pair of adjacent bits of a given number.
+ * @author Lakshyajeet Singh Goyal (https://github.com/DarkMatter-999)
+ */
+
+public final class SwapAdjacentBits {
+    private SwapAdjacentBits() {
+    }
+
+    public static int swapAdjacentBits(int num) {
+        // mask the even bits (0xAAAAAAAA => 10101010...)
+        int evenBits = num & 0xAAAAAAAA;
+
+        // mask the odd bits (0x55555555 => 01010101...)
+        int oddBits = num & 0x55555555;
+
+        // right shift even bits and left shift odd bits
+        evenBits >>= 1;
+        oddBits <<= 1;
+
+        // combine shifted bits
+        return evenBits | oddBits;
+    }
+}

src/test/java/com/thealgorithms/bitmanipulation/SwapAdjacentBitsTest.java

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+package com.thealgorithms.bitmanipulation;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+class SwapAdjacentBitsTest {
+
+    @Test
+    void testSwapAdjacentBits() {
+        assertEquals(1, SwapAdjacentBits.swapAdjacentBits(2));
+
+        assertEquals(23, SwapAdjacentBits.swapAdjacentBits(43));
+
+        assertEquals(102, SwapAdjacentBits.swapAdjacentBits(153));
+
+        assertEquals(15, SwapAdjacentBits.swapAdjacentBits(15));
+
+        assertEquals(0, SwapAdjacentBits.swapAdjacentBits(0));
+    }
+}