Dynamic Method Dispatch in Java

Author: kishanrajput23

49.Dynamic_Method_Dispatch/README.md

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+# Dynamic Method Dispatch in Java
+- Dynamic method dispatch is also known as run time polymorphism.
+- It is the process through which a call to an overridden method is resolved at runtime.
+- This technique is used to resolve a call to an overridden method at runtime rather than compile time.
+- To properly understand Dynamic method dispatch in Java, it is important to understand the concept of upcasting because dynamic method dispatch is based on upcasting.
+
+### Upcasting :
+- It is a technique in which a superclass reference variable refers to the object of the subclass.
+- Example :
+
+```
+class Animal{}  
+class Dog extends Animal{}  
+Animal a=new Dog();//upcasting  
+```
+
+- In the above example, we've created two classes, named Animal(superclass) & Dog(subclass). While creating the object 'a', we've taken the reference variable of the parent class(Animal), and the object created is of child class(Dog).
+
+### Example to demonstrate the use of Dynamic method dispatch :
+- In the below code, we've created two classes: Phone & SmartPhone.
+- The Phone is the parent class and the SmartPhone is the child class. 
+- The method on() of the parent class is overridden inside the child class.
+- Inside the main() method, we've created an object obj of the Smartphone() class by taking the reference of the Phone() class.
+- When obj.on() will be executed, it will call the on() method of the SmartPhone() class because the reference variable obj is pointing towards the object of class SmartPhone().
+
+```
+class Phone{
+    public void showTime() {
+        System.out.println("Time is 8 am");
+    }
+    public void on(){
+        System.out.println("Turning on Phone...");
+    }
+}
+
+class SmartPhone extends Phone {
+    public void music() {
+        System.out.println("Playing music...");
+    }
+    public void on() {
+        System.out.println("Turning on SmartPhone...");
+    }
+}
+
+public class CWH {
+    public static void main(String[] args) {
+
+        Phone obj = new SmartPhone(); // Yes it is allowed
+        // SmartPhone obj2 = new Phone(); // Not allowed
+
+        obj.showTime();
+        obj.on();
+        // obj.music(); Not Allowed
+    }
+}
+```
+
+```
+Output :
+Time is 8 am
+Turning on SmartPhone...
+```
+
+**Note:** The data members can not achieve the run time polymorphism.
+
+### Code as described/written in the video :
+
+```
+class Phone {
+    public void showTime() {
+        System.out.println("Time is 8 am");
+    }
+    public void on() {
+        System.out.println("Turning on Phone...");
+    }
+}
+
+class SmartPhone extends Phone {
+    public void music() {
+        System.out.println("Playing music...");
+    }
+    public void on() {
+        System.out.println("Turning on SmartPhone...");
+    }
+}
+public class cwh_49_dynamic_method_dispatch {
+    public static void main(String[] args) {
+        // Phone obj = new Phone(); // Allowed
+        // SmartPhone smobj = new SmartPhone(); // Allowed
+        // obj.name();
+
+        Phone obj = new SmartPhone(); // Yes it is allowed
+        // SmartPhone obj2 = new Phone(); // Not allowed
+
+        obj.showTime();
+        obj.on();
+        // obj.music(); Not Allowed
+    }
+}
+```
+
+**Handwritten Notes: [Click to Download](https://api.codewithharry.com/media/videoSeriesFiles/courseFiles/java-tutorials-for-beginners-49/JavaChapter10.pdf)**
+
+**Ultimate Java Cheatsheet: [Click To Download](https://api.codewithharry.com/media/videoSeriesFiles/courseFiles/java-tutorials-for-beginners-49/UltimateJavaCheatSheet.pdf)**