feat: Implement Singleton design pattern with PrivateConstructor class

WHAT the code does:
- Defines a `PrivateConstructor` class that restricts object creation.
- Declares a static field `School` to hold the single instance.
- Makes the constructor `private` so no external code can instantiate the class.
- Provides `getInstance()` method:
  - If `School` is `null`, creates a new instance.
  - Otherwise, returns the existing instance.
- `main()` repeatedly calls `getInstance()` to demonstrate that only one object is created.

WHY this matters:
- Implements the **Singleton pattern** — ensures only one instance of a class exists.
- Useful for cases like configuration managers, logging, thread pools, or database connections.
- Demonstrates **controlled object creation** using private constructors and static methods.

HOW it works:
1. First call to `getInstance()` → `School` is null → creates new `PrivateConstructor` object.
2. Later calls return the same object reference, preventing multiple creations.
3. Program ensures all callers use the same singleton instance.

Tips & gotchas:
- This is a **lazy initialization** singleton → instance created only when needed.
- Not thread-safe: multiple threads could create multiple instances at the same time.
  → Can fix with synchronized `getInstance()` or double-checked locking.
- For strict immutability, mark the singleton instance as `final` and initialize eagerly.
- Enum-based singletons in Java are simpler and thread-safe by default.

Use-cases:
- Logger classes.
- Database connection pools.
- Application configuration objects.
- Resource managers that must be globally consistent.

Short key: pattern-singleton-private constructor.

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

Author: Someshdiwan

Section10Methods/Methods 2.O/src/PrivateConstructor.java

@@ -1,26 +1,23 @@
-public class PrivateConstructor
-{
-    //Our aim is to create only one object of our class Private Constructor
-
-    private static PrivateConstructor School; //Vaiable leya hai
-    //Instance create keya hai.
-
+public class PrivateConstructor {
+    // Our aim is to create only one object of our class Private Constructor
+    private static PrivateConstructor School;
+/*
+     Variable leya hai.
+     Instance create keya hai.
+*/
 
     //Private constructor create keya hai toh object create kar nahi sakte.
-    private PrivateConstructor(){
+    private PrivateConstructor() {
 
     }
 
-    //Method....Instance return karega
-    public static PrivateConstructor getInstance()
-    {
-        if(School == null)
-        {
+    // Method....Instance return karega
+    public static PrivateConstructor getInstance() {
+        if (School == null) {
             School = new PrivateConstructor();
         }
         return School;
     }
-
     public static void main(String[] args) {
         PrivateConstructor.getInstance();
         PrivateConstructor.getInstance();
@@ -29,7 +26,9 @@ public static void main(String[] args) {
         PrivateConstructor.getInstance();
         PrivateConstructor.getInstance();
         PrivateConstructor.getInstance();
-        //Isko Bolte hai SingleTone Pattern, Ek hai object Hoga create Ek Class ka
-        //Ye Hamne Restrication Rakh Deya hai
+        /*
+         Isko Bolte hai SingleTone Pattern, Ek hai object Hoga create Ek Class ka
+         Ye Hamne Restrication Rakh Deya hai
+        */
     }
-}
+}