Java Polymorphism Quiz | 25 OOP MCQs for Interviews & Exams

STUDYECRAT Java : OOP - POLYMORPHISM

60s

Java OOP - POLYMORPHISM

Prove your skills in this interactive quiz

💻

Live Code

Run snippets directly

⏱️

Timed

60s per question

🏆

Scored

Earn 3D badges

Q1/4

What is the output?

System.out.println("Hello World");

Quiz Complete!

Great job! You're above average!

4 Correct

1:20 Time

#42 Rank

Review Answers

Want to improve your score?

Explore Studyecrat Courses →

★ Java Polymorphism: Key Interview Points

1. Runtime Polymorphism (Method Overriding)

class Animal {
  void sound() { System.out.println("Generic animal sound"); }
}
class Dog extends Animal {
  @Override
  void sound() { System.out.println("Bark!"); }
}
// JVM decides method call at runtime based on object type

• Tip: Always use @Override annotation to prevent accidental method signature mismatches
• Real Use: Used in frameworks like Spring where dependency injection resolves implementations at runtime

2. Compile-time Polymorphism (Method Overloading)

class Calculator {
  int add(int a, int b) { return a + b; }
  double add(double a, double b) { return a + b; }
  String add(String a, String b) { return a.concat(b); }
}
// Method resolution happens at compile time

• Tip: Overloaded methods should perform similar operations to avoid confusion
• Real Use: Common in utility classes like Math with abs() methods for different types

3. Interface Polymorphism

interface Payment {
  void processPayment(double amount);
}
class CreditCard implements Payment {
  public void processPayment(double amt) {
    System.out.println("Processing card: $" + amt);
  }
}
// Can hold any implementing class instance

• Tip: Use interfaces for dependency injection to enable easy testing/mocking
• Real Use: Payment gateways where implementation can vary (PayPal, Stripe, etc.)

4. Covariant Return Types

class Parent {
  Parent get() { return this; }
}
class Child extends Parent {
  @Override
  Child get() { return this; }
}
// Allowed since Java 5 - subtype can be returned

• Tip: Useful in builder pattern implementations where subclass methods return 'this'
• Real Use: Cloneable implementations often use covariant returns for type safety

5. Polymorphic Collections

List<Shape> shapes = new ArrayList<>();
shapes.add(new Circle());
shapes.add(new Rectangle());

for(Shape s : shapes) {
  s.draw(); // Calls appropriate implementation
}
// Collection holds different subclass instances

• Tip: Use generics (List<ParentType>) for type safety in polymorphic collections
• Real Use: GUI frameworks storing different UI components in a single collection

💡 Pro Interview Tip

When asked about polymorphism, always differentiate between compile-time (overloading) and runtime (overriding) polymorphism. Interviewers often test this fundamental understanding. For bonus points, mention how polymorphism enables the Open/Closed Principle in SOLID design.