Interview Q&A / Java

1. What are the four pillars of object-oriented programming in Java?

   Encapsulation hides data behind methods, abstraction exposes only what matters, inheritance reuses a parent class, and polymorphism lets one call behave differently depending on the actual object.

   BeginnerQuick answer1 min read
2. What is constructor chaining in Java and are constructors inherited?

   Constructors are not inherited. Every constructor starts by calling another one, either this(...) in the same class or super(...) in the parent, and Java inserts super() automatically if you write neither.

   BeginnerQuick answer1 min read
3. What is the difference between encapsulation and abstraction in Java?

   Abstraction hides complexity by showing only what a user needs, usually through interfaces or abstract classes. Encapsulation hides data by keeping fields private and exposing controlled methods. One is about design, the other about protection.

   BeginnerQuick answer1 min read
4. What is the difference between method overloading and method overriding in Java?

   Overloading is several methods with the same name but different parameters in one class, resolved at compile time. Overriding is a subclass replacing a parent method with the same signature, resolved at runtime.

   BeginnerQuick answer1 min read
5. Can static, private and final methods be overridden in Java?

   No. Final methods are forbidden from overriding, private methods are invisible to subclasses, and static methods belong to the class, so a same-named subclass method only hides the parent one instead of overriding it.

   IntermediateQuick answer1 min read
6. What does this Java code print when a parent reference holds a child object?

   Methods are looked up on the real object at runtime, so the child version runs. Fields are looked up on the reference type at compile time, so the parent field is read. Fields are never polymorphic.

   IntermediateQuick answer1 min read
7. When should you use composition instead of inheritance in Java?

   Use inheritance for a true is-a relationship and composition for has-a. Composition is usually safer because the classes stay loosely coupled and you can change the part at runtime, while inheritance ties the child tightly to the parent.

   IntermediateQuick answer1 min read
8. Why does Java not allow a class to extend more than one class?

   To avoid the diamond problem, where two parents define the same method and the child cannot tell which one to inherit. Java allows multiple interfaces instead, and since Java 8 a conflicting default method must be resolved explicitly.

   IntermediateQuick answer1 min read