Merge pull request #57 from IamBisrutPyne/IamBisrutPyne-fibonacci-java

Update fibonacci.java

Author: IamBisrutPyne

snippets/Basics/java/fibonacci.java

@@ -1,6 +1,57 @@
-# Title: Iterative + recursive Fibonacci
-# Topic: Basics
-# Language: java
-# Example: see bottom
+// Metadata Header (MANDATORY)
+// -----------------------------
+// Program Title: Fibonacci Sequence (Iterative)
+// Author: IamBisrutPyne
+// Date: 2025-10-11
+//
+// Description: Generates the Fibonacci sequence up to the n-th term using an iterative approach.
+//
+// Language: Java
+//
+// Time Complexity: O(n)
+// Space Complexity: O(1)
+// -----------------------------
 
-// Iterative + recursive Fibonacci - placeholder in java
+import java.util.ArrayList;
+import java.util.List;
+
+public class FibonacciIterative {
+
+    /**
+     * Generates the Fibonacci sequence up to the n-th term iteratively.
+     * Uses long to prevent integer overflow for larger sequences.
+     *
+     * @param n The number of terms to generate.
+     * @return A list of the first n Fibonacci numbers.
+     */
+    public static List<Long> generate(int n) {
+        if (n < 0) {
+            throw new IllegalArgumentException("Input must be non-negative.");
+        }
+        
+        List<Long> sequence = new ArrayList<>();
+        if (n == 0) return sequence;
+        
+        long a = 0; // F(0)
+        long b = 1; // F(1)
+
+        sequence.add(a);
+        if (n == 1) return sequence;
+
+        sequence.add(b);
+        
+        for (int i = 2; i < n; i++) {
+            long nextVal = a + b;
+            sequence.add(nextVal);
+            // Shift values
+            a = b;
+            b = nextVal;
+        }
+        return sequence;
+    }
+
+    public static void main(String[] args) {
+        int n_terms = 20;
+        System.out.println("Fibonacci sequence (first " + n_terms + " terms): " + generate(n_terms));
+    }
+}