ecd Interview Questions and Answers

1. What is the difference between a process and a thread?

   • Answer: A process is an independent, self-contained execution environment, while a thread is a lightweight unit of execution within a process. Processes have separate memory spaces, while threads within the same process share memory, leading to faster communication but increased risk of concurrency issues.

2. Explain the concept of polymorphism.

   • Answer: Polymorphism allows objects of different classes to be treated as objects of a common type. This is achieved through inheritance and interfaces. It enables writing flexible and reusable code.

3. What are the SOLID principles of object-oriented design?

   • Answer: SOLID is an acronym for five design principles: Single Responsibility Principle (one class, one responsibility), Open/Closed Principle (open for extension, closed for modification), Liskov Substitution Principle (subtypes should be substitutable for their base types), Interface Segregation Principle (many client-specific interfaces rather than one general-purpose interface), and Dependency Inversion Principle (depend on abstractions, not concretions).

4. What is the difference between == and .equals() in Java?

   • Answer: `==` compares memory addresses (for objects, whether they refer to the same object in memory), while `.equals()` compares the content of the objects. `.equals()` needs to be overridden to provide meaningful comparison for custom classes.

5. Explain the concept of inheritance.

   • Answer: Inheritance is a mechanism where a class (subclass or derived class) acquires the properties and methods of another class (superclass or base class). It promotes code reusability and establishes an "is-a" relationship between classes.

6. What is an abstract class?

   • Answer: An abstract class cannot be instantiated directly. It serves as a blueprint for subclasses and can contain abstract methods (methods without implementation) that subclasses must implement.

7. What is an interface?

   • Answer: An interface defines a contract that classes must adhere to. It specifies methods that implementing classes must provide, promoting abstraction and polymorphism.

8. What is the difference between an interface and an abstract class?

   • Answer: An interface can only have abstract methods (Java 8 and later allow default and static methods), while an abstract class can have both abstract and concrete methods. A class can implement multiple interfaces but can extend only one abstract class (in Java).

9. What is exception handling?

   • Answer: Exception handling is a mechanism to gracefully handle runtime errors (exceptions) that may occur during program execution. It uses `try`, `catch`, and `finally` blocks to manage exceptions and prevent program crashes.

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