feat(ForEachDemo): add demo of forEach with lambdas, method references, and custom filter

What
- Added ForEachDemo class.
- Created a List<Integer> with values [5,10,50,60,70,80,90].
- Demonstrated three uses of forEach():
  - With a lambda expression → prints all elements.
  - With a method reference → prints all elements in shorter syntax.
  - With a custom static helper method show() → prints only elements > 60.

Why
- Illustrates different syntaxes supported by forEach() in Java 8+.
- Demonstrates the power of method references for cleaner code.
- Shows how to integrate custom filtering logic inside helper methods.

How
- list.forEach(n -> System.out.println(n)):
  - Explicit lambda parameter, prints each element.
- list.forEach(System.out::println):
  - Method reference, shorter equivalent of the above.
- list.forEach(ForEachDemo::show):
  - Calls custom show(int n).
  - show() checks if n > 60, then prints.
- Prints sections with headings for clarity.

Logic
- Inputs: fixed list of integers.
- Outputs:
  - Prints all values via lambda and method reference.
  - Prints only values > 60 via custom method.
- Flow:
  1. Populate list.
  2. Use forEach with lambda.
  3. Use forEach with method reference.
  4. Use forEach with custom method.
- Edge cases:
  - Empty list → forEach does nothing.
  - show() filters values, so threshold logic determines output.
- Complexity: O(n) for traversal.
- Concurrency: not thread-safe for concurrent modifications.

Real-life applications
- Iterating collections in a concise, functional style.
- Method references for logging, printing, or invoking existing utilities.
- Passing custom filter/transform logic into forEach for quick one-off behaviors.

Notes
- forEach() is a terminal operation (traverses entire collection).
- Method references (::) are syntactic sugar for simple lambdas.
- For filtering large datasets, prefer streams with filter() instead of custom show().

Signed-off-by: https://github.com/Someshdiwan <[email protected]>

Author: Someshdiwan

Section 25 Collections Frameworks/List Interface/ArrayList/src/ForEachDemo.java

@@ -0,0 +1,24 @@
+import java.util.ArrayList;
+import java.util.List;
+
+/* Demonstrates forEach, method references, and a helper show() method. */
+
+public class ForEachDemo {
+    public static void main(String[] args) {
+        List<Integer> list = new ArrayList<>(List.of(5, 10, 50, 60, 70, 80, 90));
+
+        System.out.println("forEach with lambda:");
+        list.forEach(n -> System.out.println(n));
+
+        System.out.println("\nforEach with method reference:");
+        list.forEach(System.out::println);
+
+        System.out.println("\nforEach with custom show() to filter (n > 60):");
+        list.forEach(ForEachDemo::show);
+    }
+    private static void show(int n) {
+        if (n > 60) {
+            System.out.println(n);
+        }
+    }
+}