Table of Contents

Method Overriding
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Lecture 18
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Java Programming (4343203)
Diploma in ICT - Semester IV
Gujarat Technological University

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Learning Objectives
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By the end of this lecture, you will be able to:

🔄 Understand method overriding vs method overloading
🎯 Implement method overriding with @Override annotation
⚡ Apply dynamic method dispatch and runtime polymorphism
🛡️ Follow overriding rules and restrictions
🎨 Design polymorphic systems using method overriding
📝 Practice with real-world overriding scenarios

Let's master runtime polymorphism! 🔄⚡

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What is Method Overriding?
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graph TD
    A[Method Overriding] --> B[Same Method Signature]
    A --> C[Different Implementation]
    A --> D[Runtime Decision]
    
    B --> E[Same Name]
    B --> F[Same Parameters]
    B --> G[Same Return Type]
    
    C --> H[Parent Implementation]
    C --> I[Child Implementation]
    
    D --> J[Dynamic Method Dispatch]
    D --> K[Late Binding]
    
    style A fill:#e3f2fd
    style D fill:#f3e5f5

🎯 Method Overriding

• Child redefines parent method
• Same method signature required
• Runtime method selection
• Enables polymorphism

⚡ Dynamic Dispatch

• Method resolved at runtime
• Based on actual object type
• Enables flexible design
• Foundation of OOP

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Overriding vs Overloading
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🔄 Method Overriding
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// Parent class
class Animal {
    public void makeSound() {
        System.out.println("Animal makes a generic sound");
    }
    
    public void move() {
        System.out.println("Animal moves");
    }
}

// Child class - Method Overriding
class Dog extends Animal {
    @Override
    public void makeSound() {  // Same signature
        System.out.println("Dog barks: Woof! Woof!");
    }
    
    @Override
    public void move() {  // Same signature
        System.out.println("Dog runs on four legs");
    }
}

// Usage
Animal animal = new Dog();  // Polymorphism
animal.makeSound();  // Calls Dog's version (Runtime decision)
animal.move();       // Calls Dog's version (Runtime decision)

Key Features:

Same method signature
Runtime method resolution
Inheritance relationship required
Enables polymorphism

🔧 Method Overloading (Review)
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// Method Overloading in same class
class Calculator {
    // Same method name, different parameters
    public int add(int a, int b) {
        return a + b;
    }
    
    public double add(double a, double b) {  // Different types
        return a + b;
    }
    
    public int add(int a, int b, int c) {    // Different count
        return a + b + c;
    }
}

// Usage
Calculator calc = new Calculator();
calc.add(5, 10);        // Calls int version (Compile-time decision)
calc.add(5.5, 10.7);    // Calls double version (Compile-time decision)
calc.add(1, 2, 3);      // Calls three-parameter version

Key Features:

Different method signatures
Compile-time method resolution
Same class or inheritance
Static polymorphism

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Basic Method Overriding
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🎯 Simple Overriding Example
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// Base class
class Vehicle {
    protected String brand;
    protected double speed;
    
    public Vehicle(String brand) {
        this.brand = brand;
        this.speed = 0.0;
    }
    
    // Method to be overridden
    public void start() {
        System.out.println(brand + " vehicle is starting");
        speed = 10.0;
    }
    
    public void stop() {
        System.out.println(brand + " vehicle is stopping");
        speed = 0.0;
    }
    
    public void displaySpeed() {
        System.out.println("Current speed: " + speed + " km/h");
    }
    
    // Method that shows vehicle type
    public void showVehicleType() {
        System.out.println("This is a generic vehicle");
    }
}

// Derived class
class Car extends Vehicle {
    private boolean engineRunning;
    
    public Car(String brand) {
        super(brand);
        this.engineRunning = false;
    }
    
    // Override parent method
    @Override
    public void start() {
        System.out.println("Turning key to start " + brand + " car");
        System.out.println("Engine started!");
        engineRunning = true;
        speed = 15.0;  // Car starts faster than generic vehicle
    }
    
    // Override parent method
    @Override
    public void stop() {
        System.out.println("Applying brakes on " + brand + " car");
        System.out.println("Engine stopped!");
        engineRunning = false;
        speed = 0.0;
    }
    
    // Override parent method
    @Override
    public void showVehicleType() {
        System.out.println("This is a car - " + brand);
    }
}

🚗 Overriding in Action
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public class OverridingDemo {
    public static void main(String[] args) {
        // Direct object creation
        System.out.println("=== Direct Object Creation ===");
        Car car = new Car("Toyota");
        car.start();        // Calls Car's overridden method
        car.displaySpeed(); // Inherited from Vehicle
        car.showVehicleType(); // Calls Car's overridden method
        car.stop();         // Calls Car's overridden method
        
        System.out.println("\n=== Polymorphic Behavior ===");
        // Polymorphic reference - Vehicle reference to Car object
        Vehicle vehicle = new Car("Honda");
        
        // All these calls go to Car's overridden methods
        vehicle.start();        // Car's start() method
        vehicle.displaySpeed(); // Vehicle's method (inherited)
        vehicle.showVehicleType(); // Car's overridden method
        vehicle.stop();         // Car's overridden method
        
        System.out.println("\n=== Method Resolution Verification ===");
        System.out.println("Object type: " + vehicle.getClass().getSimpleName());
        System.out.println("Reference type: Vehicle");
        System.out.println("Methods called are from: " + 
                          vehicle.getClass().getSimpleName());
    }
}

Expected Output:

=== Direct Object Creation ===
Turning key to start Toyota car
Engine started!
Current speed: 15.0 km/h
This is a car - Toyota
Applying brakes on Toyota car
Engine stopped!

=== Polymorphic Behavior ===
Turning key to start Honda car
Engine started!
Current speed: 15.0 km/h
This is a car - Honda
Applying brakes on Honda car
Engine stopped!

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@Override Annotation
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🛡️ Benefits of @Override
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Compile-time Safety:

Ensures method actually overrides parent method
Catches typos in method names
Validates method signatures

Code Documentation:

Clear intent to override
Helps other developers understand
IDE support and warnings

Refactoring Safety:

Alerts if parent method signature changes
Prevents accidental method hiding
Maintains inheritance contracts

❌ Without @Override
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class Animal {
    public void makeSound() {
        System.out.println("Animal sound");
    }
}

class Cat extends Animal {
    // Typo in method name - no compilation error!
    public void makesound() {  // Missing capital S
        System.out.println("Cat meows");
    }
}

// Usage
Animal cat = new Cat();
cat.makeSound();  // Prints "Animal sound" - not what we wanted!

✅ With @Override
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class Animal {
    public void makeSound() {
        System.out.println("Animal sound");
    }
    
    public void sleep(int hours) {
        System.out.println("Animal sleeps for " + hours + " hours");
    }
}

class Cat extends Animal {
    @Override
    public void makeSound() {  // ✅ Correct override
        System.out.println("Cat meows");
    }
    
    // This would cause compilation error
    // @Override
    // public void makesound() {  // ❌ Method doesn't exist in parent
    //     System.out.println("Cat meows");
    // }
    
    @Override
    public void sleep(int hours) {  // ✅ Correct override
        System.out.println("Cat sleeps curled up for " + hours + " hours");
    }
    
    // This would cause compilation error  
    // @Override
    // public void sleep(double hours) {  // ❌ Different parameter type
    //     System.out.println("Cat sleeps");
    // }
}

// Safe usage
Animal cat = new Cat();
cat.makeSound();  // ✅ Guaranteed to call Cat's method
cat.sleep(8);     // ✅ Guaranteed to call Cat's method

🎯 Best Practice: Always use @Override annotation when overriding methods!

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Method Overriding Rules
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📜 Overriding Rules
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Method Signature:

Method name must be identical
Parameter list must be identical
Return type must be same or covariant

Access Modifiers:

Cannot reduce visibility
Can increase visibility
private methods cannot be overridden

Exceptions:

Cannot throw new checked exceptions
Can throw fewer or narrower exceptions
Unchecked exceptions have no restrictions

Other Rules:

static methods cannot be overridden (hidden instead)
final methods cannot be overridden
Constructor cannot be overridden

📝 Rules Demonstration
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class Parent {
    // Protected method
    protected void method1() throws IOException {
        System.out.println("Parent method1");
    }
    
    // Public method with return type
    public Number method2() {
        return Integer.valueOf(10);
    }
    
    // Final method - cannot be overridden
    public final void method3() {
        System.out.println("Final method");
    }
    
    // Static method - can be hidden, not overridden
    public static void method4() {
        System.out.println("Parent static method");
    }
    
    // Private method - not inherited, cannot be overridden
    private void method5() {
        System.out.println("Private method");
    }
}

class Child extends Parent {
    // ✅ Valid override - increased visibility
    @Override
    public void method1() {  // protected → public (allowed)
        System.out.println("Child method1");
        // No exception thrown (allowed - fewer exceptions)
    }
    
    // ✅ Valid override - covariant return type
    @Override
    public Integer method2() {  // Number → Integer (covariant)
        return Integer.valueOf(20);
    }
    
    // ❌ This would cause compilation error
    // @Override
    // public void method3() {  // Cannot override final method
    //     System.out.println("Child method3");
    // }
    
    // ✅ Method hiding (not overriding)
    public static void method4() {
        System.out.println("Child static method");
    }
    
    // ✅ New method (not overriding private method)
    public void method5() {
        System.out.println("Child method5");
    }
}

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Dynamic Method Dispatch
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⚡ Runtime Method Resolution
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// Demonstration of dynamic method dispatch
class Shape {
    protected String name;
    
    public Shape(String name) {
        this.name = name;
    }
    
    public void draw() {
        System.out.println("Drawing a generic shape: " + name);
    }
    
    public double calculateArea() {
        System.out.println("Area calculation not implemented for generic shape");
        return 0.0;
    }
    
    public void displayInfo() {
        System.out.println("Shape: " + name);
        System.out.println("Area: " + calculateArea());
    }
}

class Circle extends Shape {
    private double radius;
    
    public Circle(double radius) {
        super("Circle");
        this.radius = radius;
    }
    
    @Override
    public void draw() {
        System.out.println("Drawing a circle with radius: " + radius);
    }
    
    @Override
    public double calculateArea() {
        double area = Math.PI * radius * radius;
        System.out.println("Calculating circle area: π × " + radius + "²");
        return area;
    }
}

class Rectangle extends Shape {
    private double width, height;
    
    public Rectangle(double width, double height) {
        super("Rectangle");
        this.width = width;
        this.height = height;
    }
    
    @Override
    public void draw() {
        System.out.println("Drawing a rectangle: " + width + " × " + height);
    }
    
    @Override
    public double calculateArea() {
        double area = width * height;
        System.out.println("Calculating rectangle area: " + width + " × " + height);
        return area;
    }
}

🎭 Polymorphic Behavior
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public class DynamicDispatchDemo {
    public static void main(String[] args) {
        // Array of Shape references pointing to different objects
        Shape[] shapes = {
            new Circle(5.0),
            new Rectangle(4.0, 6.0),
            new Circle(3.0),
            new Rectangle(10.0, 2.0)
        };
        
        System.out.println("=== Dynamic Method Dispatch Demo ===");
        
        // Same method call, different implementations executed
        for (Shape shape : shapes) {
            System.out.println("\n--- Processing " + shape.name + " ---");
            
            // These method calls are resolved at runtime
            shape.draw();        // Calls appropriate draw() method
            shape.displayInfo(); // Uses overridden calculateArea()
            
            // Verify actual object type
            System.out.println("Actual object type: " + 
                             shape.getClass().getSimpleName());
        }
        
        System.out.println("\n=== Method Resolution Details ===");
        demonstrateMethodResolution();
    }
    
    private static void demonstrateMethodResolution() {
        Shape shape1 = new Circle(7.0);
        Shape shape2 = new Rectangle(5.0, 8.0);
        
        // Same reference type, different object types
        System.out.println("shape1 reference type: Shape");
        System.out.println("shape1 object type: " + shape1.getClass().getSimpleName());
        shape1.calculateArea();  // Calls Circle's method
        
        System.out.println("\nshape2 reference type: Shape");
        System.out.println("shape2 object type: " + shape2.getClass().getSimpleName());
        shape2.calculateArea();  // Calls Rectangle's method
        
        // Method binding happens at runtime based on actual object type
        System.out.println("\nMethod binding: RUNTIME (Dynamic)");
    }
}

Key Points:

Method resolution happens at runtime
Based on actual object type, not reference type
Enables true polymorphic behavior
Foundation of flexible OOP design

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Real-World Example: Employee Management System
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👥 Employee Hierarchy with Overriding
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abstract class Employee {
    protected String employeeId;
    protected String name;
    protected String department;
    protected double baseSalary;
    
    public Employee(String employeeId, String name, String department, double baseSalary) {
        this.employeeId = employeeId;
        this.name = name;
        this.department = department;
        this.baseSalary = baseSalary;
    }
    
    // Methods to be overridden by subclasses
    public abstract double calculateSalary();
    public abstract void displayRole();
    
    // Common method that can be overridden
    public void clockIn() {
        System.out.println(name + " (" + employeeId + ") clocked in at " + 
                          java.time.LocalTime.now());
    }
    
    public void displayBasicInfo() {
        System.out.println("ID: " + employeeId);
        System.out.println("Name: " + name);
        System.out.println("Department: " + department);
        System.out.println("Base Salary: $" + baseSalary);
    }
    
    // Template method using overridden methods
    public void generatePaySlip() {
        System.out.println("=== PAY SLIP ===");
        displayBasicInfo();
        displayRole();
        System.out.println("Total Salary: $" + String.format("%.2f", calculateSalary()));
        System.out.println("================");
    }
}

class Manager extends Employee {
    private double bonusPercentage;
    private int teamSize;
    
    public Manager(String employeeId, String name, String department, 
                  double baseSalary, double bonusPercentage, int teamSize) {
        super(employeeId, name, department, baseSalary);
        this.bonusPercentage = bonusPercentage;
        this.teamSize = teamSize;
    }
    
    @Override
    public double calculateSalary() {
        double bonus = baseSalary * bonusPercentage;
        double teamBonus = teamSize * 100; // $100 per team member
        return baseSalary + bonus + teamBonus;
    }
    
    @Override
    public void displayRole() {
        System.out.println("Role: Manager");
        System.out.println("Team Size: " + teamSize);
        System.out.println("Bonus Percentage: " + (bonusPercentage * 100) + "%");
    }
    
    @Override
    public void clockIn() {
        System.out.println("Manager " + name + " accessed management portal");
        super.clockIn(); // Call parent implementation
    }
}

💻 Developer and Sales Classes
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class Developer extends Employee {
    private String programmingLanguage;
    private int projectsCompleted;
    
    public Developer(String employeeId, String name, double baseSalary, 
                    String language, int projectsCompleted) {
        super(employeeId, name, "IT", baseSalary);
        this.programmingLanguage = language;
        this.projectsCompleted = projectsCompleted;
    }
    
    @Override
    public double calculateSalary() {
        double projectBonus = projectsCompleted * 500; // $500 per project
        return baseSalary + projectBonus;
    }
    
    @Override
    public void displayRole() {
        System.out.println("Role: Software Developer");
        System.out.println("Programming Language: " + programmingLanguage);
        System.out.println("Projects Completed: " + projectsCompleted);
    }
    
    @Override
    public void clockIn() {
        System.out.println("Developer " + name + " started coding session");
        super.clockIn();
    }
}

class SalesRepresentative extends Employee {
    private double commissionRate;
    private double salesAmount;
    
    public SalesRepresentative(String employeeId, String name, double baseSalary,
                              double commissionRate, double salesAmount) {
        super(employeeId, name, "Sales", baseSalary);
        this.commissionRate = commissionRate;
        this.salesAmount = salesAmount;
    }
    
    @Override
    public double calculateSalary() {
        double commission = salesAmount * commissionRate;
        return baseSalary + commission;
    }
    
    @Override
    public void displayRole() {
        System.out.println("Role: Sales Representative");
        System.out.println("Commission Rate: " + (commissionRate * 100) + "%");
        System.out.println("Sales Amount: $" + salesAmount);
    }
    
    @Override
    public void clockIn() {
        System.out.println("Sales Rep " + name + " checked sales dashboard");
        super.clockIn();
    }
}

// Payroll system using polymorphism
class PayrollSystem {
    public static void processPayroll(Employee[] employees) {
        System.out.println("=== MONTHLY PAYROLL PROCESSING ===\n");
        
        double totalPayroll = 0.0;
        
        for (Employee emp : employees) {
            emp.clockIn();           // Different implementation for each type
            emp.generatePaySlip();   // Uses overridden calculateSalary()
            totalPayroll += emp.calculateSalary();
            System.out.println();
        }
        
        System.out.println("Total Payroll: $" + String.format("%.2f", totalPayroll));
    }
}

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Covariant Return Types
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🔄 Return Type Flexibility
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// Base class
class Animal {
    public Animal reproduce() {
        System.out.println("Animal reproduces");
        return new Animal();
    }
    
    public void showType() {
        System.out.println("This is an Animal");
    }
}

// Child class with covariant return type
class Dog extends Animal {
    @Override
    public Dog reproduce() {  // ✅ Covariant return type
        System.out.println("Dog reproduces");
        return new Dog();  // Returns Dog instead of Animal
    }
    
    @Override
    public void showType() {
        System.out.println("This is a Dog");
    }
    
    public void bark() {
        System.out.println("Dog barks");
    }
}

class Cat extends Animal {
    @Override
    public Cat reproduce() {  // ✅ Covariant return type
        System.out.println("Cat reproduces");
        return new Cat();
    }
    
    @Override
    public void showType() {
        System.out.println("This is a Cat");
    }
    
    public void meow() {
        System.out.println("Cat meows");
    }
}

🎯 Covariant Return Benefits
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public class CovariantReturnDemo {
    public static void main(String[] args) {
        System.out.println("=== Covariant Return Type Demo ===");
        
        // Using polymorphic references
        Animal animal1 = new Dog();
        Animal animal2 = new Cat();
        
        // Method calls return Animal reference (compile-time type)
        Animal offspring1 = animal1.reproduce();  // Actually returns Dog
        Animal offspring2 = animal2.reproduce();  // Actually returns Cat
        
        offspring1.showType();  // Shows "This is a Dog"
        offspring2.showType();  // Shows "This is a Cat"
        
        System.out.println("\n=== Direct Object References ===");
        
        // Using direct references
        Dog dog = new Dog();
        Cat cat = new Cat();
        
        // Method calls return specific types (no casting needed)
        Dog puppy = dog.reproduce();    // Returns Dog directly
        Cat kitten = cat.reproduce();   // Returns Cat directly
        
        puppy.bark();   // Can call Dog-specific methods
        kitten.meow();  // Can call Cat-specific methods
        
        System.out.println("\n=== Type Verification ===");
        System.out.println("offspring1 actual type: " + offspring1.getClass().getSimpleName());
        System.out.println("offspring2 actual type: " + offspring2.getClass().getSimpleName());
        System.out.println("puppy type: " + puppy.getClass().getSimpleName());
        System.out.println("kitten type: " + kitten.getClass().getSimpleName());
    }
}

Benefits of Covariant Return Types:

No need for explicit casting
Type safety at compile time
More specific return types
Better API design
Natural inheritance hierarchy

🎯 Rule: Return type can be a subtype of the parent's return type!

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Method Hiding vs Method Overriding
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🔄 Instance Method Overriding
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class Parent {
    // Instance method - can be overridden
    public void instanceMethod() {
        System.out.println("Parent instance method");
    }
    
    // Static method - will be hidden, not overridden
    public static void staticMethod() {
        System.out.println("Parent static method");
    }
}

class Child extends Parent {
    // Method overriding - runtime dispatch
    @Override
    public void instanceMethod() {
        System.out.println("Child instance method");
    }
    
    // Method hiding - compile-time dispatch
    public static void staticMethod() {
        System.out.println("Child static method");
    }
}

public class HidingVsOverridingDemo {
    public static void main(String[] args) {
        // Instance method overriding
        System.out.println("=== Instance Method Overriding ===");
        Parent parent1 = new Parent();
        Parent parent2 = new Child();  // Polymorphic reference
        Child child = new Child();
        
        parent1.instanceMethod();  // "Parent instance method"
        parent2.instanceMethod();  // "Child instance method" (OVERRIDDEN)
        child.instanceMethod();    // "Child instance method"
        
        System.out.println("\n=== Static Method Hiding ===");
        
        // Static method hiding
        Parent.staticMethod();     // "Parent static method"
        Child.staticMethod();      // "Child static method"
        
        // Static methods are resolved at compile time
        parent1.staticMethod();    // "Parent static method"
        parent2.staticMethod();    // "Parent static method" (HIDDEN, not overridden)
        child.staticMethod();      // "Child static method"
    }
}

📊 Comparison Table
#

Aspect	Method Overriding	Method Hiding
Method Type	Instance methods	Static methods
Binding Time	Runtime (Late)	Compile-time (Early)
Keyword	@Override	No annotation
Resolution	Based on object type	Based on reference type
Polymorphism	✅ Enabled	❌ Not enabled

🎯 Practical Implications
#

class Utility {
    public static void process() {
        System.out.println("Generic processing");
    }
    
    public void execute() {
        System.out.println("Generic execution");
    }
}

class SpecializedUtility extends Utility {
    // Method hiding
    public static void process() {
        System.out.println("Specialized processing");
    }
    
    // Method overriding
    @Override
    public void execute() {
        System.out.println("Specialized execution");
    }
}

// Usage patterns
public void demonstrate() {
    Utility util1 = new SpecializedUtility();
    
    // Static method - resolved by reference type
    util1.process();    // "Generic processing" (HIDING)
    
    // Instance method - resolved by object type
    util1.execute();    // "Specialized execution" (OVERRIDING)
}

⚠️ Important: Static methods cannot be overridden, only hidden! Use instance methods for true polymorphism.

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Practical Exercise: Media Player System
#

🎵 Design Challenge
#

Requirements:

Create an abstract MediaPlayer base class
Implement different media players with overridden methods
Use @Override annotation properly
Demonstrate dynamic method dispatch
Include covariant return types where appropriate
Show polymorphic behavior in action

public abstract class MediaPlayer {
    // TODO: Common properties (name, currentTrack, volume, etc.)
    // TODO: Abstract methods (play, pause, stop, loadMedia)
    // TODO: Concrete methods that use abstract methods
    // TODO: Template method pattern implementation
}

public class AudioPlayer extends MediaPlayer {
    // TODO: Audio-specific properties and methods
    // TODO: Override abstract methods with audio implementation
    // TODO: Add audio-specific functionality
}

public class VideoPlayer extends MediaPlayer {
    // TODO: Video-specific properties and methods  
    // TODO: Override abstract methods with video implementation
    // TODO: Add video-specific functionality
}

// TODO: Create demonstration class showing polymorphism

🎯 Expected Implementation
#

Features to Implement:

Abstract MediaPlayer base class with template methods
AudioPlayer and VideoPlayer concrete implementations
Method overriding with @Override annotation
Dynamic method dispatch demonstration
Covariant return types where applicable
Polymorphic collection of different players

Success Criteria:

All abstract methods properly overridden
@Override annotation used correctly
Dynamic method dispatch working
Polymorphic behavior demonstrated
Template method pattern implemented
Real-world applicability shown

Usage Example:

// Should work after implementation
MediaPlayer[] players = {
    new AudioPlayer("Spotify"),
    new VideoPlayer("YouTube"), 
    new AudioPlayer("iTunes")
};

for (MediaPlayer player : players) {
    player.loadMedia("sample_file");  // Polymorphic call
    player.play();                    // Dynamic dispatch
    player.displayStatus();           // Template method
}

// Demonstrate covariant return types
AudioPlayer audioPlayer = new AudioPlayer("Pandora");
AudioTrack track = audioPlayer.getCurrentTrack(); // Covariant return

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Common Method Overriding Mistakes
#

❌ Method Overriding Pitfalls

```java // WRONG: Different parameter types (overloading, not overriding) class Parent { public void method(int x) { } } class Child extends Parent { @Override // ❌ Compilation error public void method(double x) { } // Different parameter type }

// WRONG: Reducing access visibility class Parent { public void method() { } } class Child extends Parent { @Override protected void method() { } // ❌ Cannot reduce visibility }

// WRONG: Adding checked exceptions class Parent { public void method() { } } class Child extends Parent { @Override public void method() throws IOException { } // ❌ New checked exception }

</div>
<div>
```java
// WRONG: Trying to override static methods
class Parent {
    public static void method() { }
}
class Child extends Parent {
    @Override  // ❌ Compilation error
    public static void method() { }  // Cannot override static
}

// WRONG: Trying to override final methods
class Parent {
    public final void method() { }
}
class Child extends Parent {
    @Override  // ❌ Compilation error
    public void method() { }  // Cannot override final
}

// WRONG: Not using @Override annotation
class Child extends Parent {
    public void method() { }  // ❌ Missing @Override, prone to errors
}

✅ Correct Approaches

```java // CORRECT: Same parameter types for overriding class Parent { public void method(int x) { } } class Child extends Parent { @Override public void method(int x) { } // ✅ Same signature }

// CORRECT: Maintaining or increasing visibility class Parent { protected void method() { } } class Child extends Parent { @Override public void method() { } // ✅ Increased visibility }

// CORRECT: Not adding new checked exceptions class Parent { public void method() throws IOException { } } class Child extends Parent { @Override public void method() { } // ✅ Fewer exceptions allowed }

</div>
<div>
```java
// CORRECT: Method hiding for static methods
class Parent {
    public static void method() { }
}
class Child extends Parent {
    // Method hiding (no @Override)
    public static void method() { }  // ✅ Hiding, not overriding
}

// CORRECT: Cannot override final - create new method
class Parent {
    public final void method() { }
}
class Child extends Parent {
    public void alternativeMethod() { }  // ✅ New method instead
}

// CORRECT: Always use @Override
class Child extends Parent {
    @Override
    public void method() { }  // ✅ Safe overriding
}

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#

Summary
#

📖 What We Learned

• Method overriding vs method overloading
• @Override annotation benefits and usage
• Dynamic method dispatch and runtime binding
• Method overriding rules and restrictions
• Covariant return types
• Method hiding vs method overriding

🎯 Next Steps

• super keyword and constructor chaining
• Abstract classes and methods
• Interface implementation and overriding
• Polymorphism and design patterns
• Advanced OOP concepts

Method overriding mastered! Ready for super keyword! 🔄⚡

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#

Questions & Discussion
#

❓

Any questions about method overriding, dynamic dispatch, or polymorphic behavior?

Next lecture: **super Keyword and Constructor Chaining**

Ready to master the super keyword! 👏

Method Overriding#

Lecture 18#

layout: default#

Learning Objectives#

layout: center#

What is Method Overriding?#

🎯 Method Overriding

⚡ Dynamic Dispatch

layout: default#

Overriding vs Overloading#

🔄 Method Overriding#

🔧 Method Overloading (Review)#

layout: default#

Basic Method Overriding#

🎯 Simple Overriding Example#

🚗 Overriding in Action#

layout: default#

@Override Annotation#

🛡️ Benefits of @Override#

❌ Without @Override#

✅ With @Override#

layout: default#

Method Overriding Rules#

📜 Overriding Rules#

📝 Rules Demonstration#

layout: default#

Dynamic Method Dispatch#

⚡ Runtime Method Resolution#

🎭 Polymorphic Behavior#

layout: default#

Real-World Example: Employee Management System#

👥 Employee Hierarchy with Overriding#

💻 Developer and Sales Classes#

layout: default#

Covariant Return Types#

🔄 Return Type Flexibility#

🎯 Covariant Return Benefits#

layout: default#

Method Hiding vs Method Overriding#

🔄 Instance Method Overriding#

📊 Comparison Table#

🎯 Practical Implications#

layout: default#

Practical Exercise: Media Player System#

🎵 Design Challenge#

🎯 Expected Implementation#

layout: default#

Common Method Overriding Mistakes#

❌ Method Overriding Pitfalls

✅ Correct Approaches

layout: center class: text-center#

Summary#

📖 What We Learned

🎯 Next Steps

layout: center class: text-center#

Questions & Discussion#

Method Overriding
#

Lecture 18
#

layout: default
#

Learning Objectives
#

layout: center
#

What is Method Overriding?
#

layout: default
#

Overriding vs Overloading
#

🔄 Method Overriding
#

🔧 Method Overloading (Review)
#

layout: default
#

Basic Method Overriding
#

🎯 Simple Overriding Example
#

🚗 Overriding in Action
#

layout: default
#

@Override Annotation
#

🛡️ Benefits of @Override
#

❌ Without @Override
#

✅ With @Override
#

layout: default
#

Method Overriding Rules
#

📜 Overriding Rules
#

📝 Rules Demonstration
#

layout: default
#

Dynamic Method Dispatch
#

⚡ Runtime Method Resolution
#

🎭 Polymorphic Behavior
#

layout: default
#

Real-World Example: Employee Management System
#

👥 Employee Hierarchy with Overriding
#

💻 Developer and Sales Classes
#

layout: default
#

Covariant Return Types
#

🔄 Return Type Flexibility
#

🎯 Covariant Return Benefits
#

layout: default
#

Method Hiding vs Method Overriding
#

🔄 Instance Method Overriding
#

📊 Comparison Table
#

🎯 Practical Implications
#

layout: default
#

Practical Exercise: Media Player System
#

🎵 Design Challenge
#

🎯 Expected Implementation
#

layout: default
#

Common Method Overriding Mistakes
#

layout: center class: text-center
#

Summary
#

layout: center class: text-center
#

Questions & Discussion
#