STUDYECRAT Java : OOP - INEHRITANCE
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Java : OOP - INEHRITANCE
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★ Java Inheritance: Key Interview Points
1. Dynamic Method Dispatch
class Animal {
void sound() { System.out.print("Generic Sound"); }
}
class Dog extends Animal {
@Override void sound() { System.out.print("Bark"); }
}
Animal myPet = new Dog();
myPet.sound(); // Output: Bark
// Runtime polymorphism in action
void sound() { System.out.print("Generic Sound"); }
}
class Dog extends Animal {
@Override void sound() { System.out.print("Bark"); }
}
Animal myPet = new Dog();
myPet.sound(); // Output: Bark
// Runtime polymorphism in action
- Tip: Use @Override annotation to prevent accidental method signature mismatches
- Real Use: Plugin architectures where child classes provide specific implementations
2. Field Shadowing
class Parent {
int value = 10;
}
class Child extends Parent {
int value = 20; // Shadows parent's field
}
Parent obj = new Child();
System.out.print(obj.value); // Output: 10
// Variables don't participate in polymorphism
int value = 10;
}
class Child extends Parent {
int value = 20; // Shadows parent's field
}
Parent obj = new Child();
System.out.print(obj.value); // Output: 10
// Variables don't participate in polymorphism
- Tip: Avoid field shadowing - use different names or protected access
- Real Use: Configuration classes where default values might be overridden
3. Constructor Inheritance
class Vehicle {
Vehicle() { System.out.print("Vehicle "); }
}
class Car extends Vehicle {
Car() { System.out.print("Car"); }
}
new Car(); // Output: Vehicle Car
// Parent constructor always executes first
Vehicle() { System.out.print("Vehicle "); }
}
class Car extends Vehicle {
Car() { System.out.print("Car"); }
}
new Car(); // Output: Vehicle Car
// Parent constructor always executes first
- Tip: Use super(params) to call specific parent constructors
- Real Use: Initializing common resources in base class constructors
4. Accessing Parent Members
class Phone {
void call() { System.out.print("Calling"); }
}
class SmartPhone extends Phone {
@Override void call() {
super.call(); // Parent implementation
System.out.print(" with Video");
}
}
new SmartPhone().call(); // Output: Calling with Video
// Extending functionality while reusing parent logic
void call() { System.out.print("Calling"); }
}
class SmartPhone extends Phone {
@Override void call() {
super.call(); // Parent implementation
System.out.print(" with Video");
}
}
new SmartPhone().call(); // Output: Calling with Video
// Extending functionality while reusing parent logic
- Tip: super() must be the first statement in constructor if used
- Real Use: Middleware implementations that wrap core functionality
5. Preventing Inheritance
final class SecurityKey { /* Cannot be extended */ }
class PaymentProcessor {
final void validate() { /* Critical security logic */ }
}
class PayPal extends PaymentProcessor {
// Compile Error: Cannot override final method
}
// Final restricts extension for security/design
class PaymentProcessor {
final void validate() { /* Critical security logic */ }
}
class PayPal extends PaymentProcessor {
// Compile Error: Cannot override final method
}
// Final restricts extension for security/design
- Tip: Mark utility classes and security methods as final
- Real Use: Immutable classes like String in Java standard library
💡 Pro Interview Tip
When asked about inheritance, always mention the "is-a" relationship principle. For example: "A Dog is-a Animal" justifies inheritance, while "Car has-a Engine" suggests composition instead.
