feat(FunctionalProgramming): add Main3 demonstrating Predicate with String condition

What
- Added Main3 class in package FunctionalProgramming.
- Demonstrates Predicate<String> with lambda:
  - startsWithLetterV → true if first character is 'v' (case-insensitive).
- Tests predicate on string "Jack" and prints result (false).

Why
- Shows how lambdas can be stored as variables representing functions.
- Illustrates functional programming concept: functions as first-class citizens in Java.
- Demonstrates applying Predicate to strings rather than numbers.

How
- Defined Predicate<String> startsWithLetterV = x -> x.toLowerCase().charAt(0) == 'v'.
- Called startsWithLetterV.test("Jack").
- Printed result to console.

Logic
- Input: string "Jack".
- Output: false.
- Flow:
  1. Input string "Jack".
  2. Convert to lowercase → "jack".
  3. Take first character → 'j'.
  4. Compare with 'v' → false.
  5. Print false.
- Edge cases:
  - Empty string would cause StringIndexOutOfBoundsException at charAt(0).
  - Null input would cause NullPointerException.
- Complexity / performance: O(1) operations.
- Concurrency / thread-safety: Predicate is stateless, thread-safe.
- Error handling: Not present; unsafe for null or empty input.

Real-life applications
- Validating user input (e.g., checking prefixes of strings).
- Filtering lists of names in streams with startsWithLetterV predicate.
- Reusable predicates for business logic (prefix/suffix conditions).

Notes
- Comment notes correctly describe that lambdas represent functions stored in variables.
- This can be extended by combining predicates with and(), or(), negate().
- For production-safe code, add null/empty checks before charAt(0).

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

Author: Someshdiwan

Java 8 Crash Course/Predicate/src/FunctionalProgramming/Main3.java

@@ -0,0 +1,14 @@
+package FunctionalProgramming;
+
+import java.util.function.Predicate;
+
+public class Main3 {
+    public static void main(String[] args) {
+        // Predicate<Integer> isEven = x % 2 == 0;
+        // Lambda Expression and We can also say that is Function.
+        // We are storing a function as a Variable.
+
+        Predicate<String> startsWithLetterV = x -> x.toLowerCase().charAt(0) == 'v';
+        System.out.println(startsWithLetterV.test("Jack"));
+    }
+}