feat(SupplierDemo): add demo using Supplier functional interface

What
- Added SupplierDemo class to demonstrate java.util.function.Supplier.
- Declared Supplier<String> giveHelloWorld returning constant string "Hello World".
- Invoked get() method and printed result.

Why
- Shows how Supplier represents a provider of values without taking input parameters.
- Demonstrates simplest use case: returning a fixed value.
- Educational example introducing Supplier in functional programming context.

How
- Created lambda expression () -> "Hello World" implementing Supplier<String>.
- Called giveHelloWorld.get() to retrieve value.
- Printed "Hello World" to stdout.

Logic
- Inputs: none (Supplier takes no arguments).
- Outputs: "Hello World".
- Flow:
  1. Supplier initialized with lambda returning string.
  2. get() called on supplier.
  3. Value printed to console.
- Edge cases: none in this case since value is constant.
- Complexity / performance: O(1) operation.
- Concurrency / thread-safety: Supplier here is stateless and thread-safe.
- Error handling: no exceptions expected.

Real-life applications
- Delayed/lazy computation of values (on-demand).
- Supplying default values in case of missing data.
- Used with Optional.orElseGet(Supplier) for fallback logic.
- Common in factory methods or configuration loaders.

Notes
- Example demonstrates constant supplier; in real scenarios, Supplier often generates dynamic values (UUIDs, timestamps, random numbers).
- Suppliers are building blocks for lazy evaluation in functional pipelines.

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

Author: Someshdiwan

JAVA8/ConsumerSupplier/src/SupplierDemo.java renamed to Java 8 Crash Course/Supplier/src/SupplierDemo.java

@@ -1,12 +1,8 @@
-import java.util.function.Consumer;
-import java.util.function.Function;
-import java.util.function.Predicate;
 import java.util.function.Supplier;
 
 public class SupplierDemo {
     public static void main(String[] args) {
-        //This is used in Database connectivity.
         Supplier<String> giveHelloWorld = () -> "Hello World";
         System.out.println(giveHelloWorld.get());
     }
-}
+}