feat: serialize array of Customer objects to file

WHAT:
- Added `WriteData` class to demonstrate serialization of multiple objects.
- Created an array of `Customer` objects with unique IDs, names, and phone numbers.
- Used `ObjectOutputStream` to serialize and persist the entire array into `Customer2.txt`.

WHY:
- To simplify serialization by writing an entire object array at once instead of looping over individual objects.
- Demonstrates how Java’s serialization mechanism handles arrays of custom objects.

KEY POINTS:
- `Customer` implements `Serializable` so its objects can be persisted.
- `static int count` ensures unique `custID` generation for each new customer.
- `writeObject(list)` serializes the array and all contained objects in one step.
- Output file is binary format, not human-readable, but can be deserialized back to objects.

REAL-WORLD USE CASES:
- Storing customer records in files before saving to a database.
- Exporting application state or session data for later recovery.
- Simple persistence mechanism for desktop or embedded applications.

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

Author: Someshdiwan

Section23JavaIOStreams/Serialisation Storing Data in a File/src/WriteData.java

@@ -0,0 +1,39 @@
+import java.io.*;
+
+class WriteCustomerData implements Serializable {
+    String custID;
+    String name;
+    String phno;
+
+    static int count = 1;
+
+    void Customer(String n, String p) {
+        custID = "C" + count;  // Unique ID
+        count++;
+        name = n;
+        phno = p;
+    }
+
+    public String toString() {
+        return "Customer ID: " + custID + "\nName: " + name + "\nPhno: " + phno + "\n";
+    }
+}
+
+public class WriteData {
+    public static void main(String[] args) throws Exception {
+        Customer list[] = {
+                new Customer("Smith", "123456789"),
+                new Customer("Johnson", "1234567"),
+                new Customer("Ajay", "12345345")
+        };
+
+        FileOutputStream fos = new FileOutputStream("/Users/somesh/Java SE/JavaEvolution-Learning-Growing-Mastering/Section23JavaIOStreams/src/MyJAVA/Customer2.txt");
+        ObjectOutputStream oos = new ObjectOutputStream(fos);
+
+        oos.writeObject(list);  // Serialize the entire array at once
+        oos.close();
+        fos.close();
+
+        System.out.println("Customer data serialized successfully.");
+    }
+}