JAVA TECHNICAL QUESTION AND ANSWERS FOR INTERVIEW PART III (Classes & Objects)

Summary

This video covers important Java technical questions related to classes and objects, crucial for interviews. It explains key concepts like the definition of a class as a blueprint that defines object properties and behaviors, and the role of objects as instances of classes. It discusses constructors, including their types and usage, and highlights how constructors initialize objects. The script also touches on final keywords, method overloading, destructors, and the use of 'this' and 'super' keywords in Java, providing clear and concise explanations for each topic.

Takeaways

• 🧱 A class in Java is a blueprint that defines properties (instance variables) and behaviors (methods) for objects.
• 👤 An object is an instance of a class and is required to access instance variables and methods. It is a runtime entity for a class.
• 🆕 The 'new' keyword in Java is used to allocate memory for an object at runtime, enabling dynamic memory allocation.
• 🔧 A constructor is a special method in Java used to initialize objects, often with default values for instance variables.
• 🚪 Constructors are automatically called when an object is created using the 'new' keyword, without the need for explicit invocation.
• 🔄 Java has two types of constructors: default constructors (without parameters) and parameterized constructors (with parameters).
• ⚙️ Constructor overloading allows a class to have multiple constructors with different parameter sets, providing flexibility.
• 🚫 Java does not have destructors. Instead, garbage collection automatically deallocates memory when objects are no longer in use.
• 🔒 The 'final' keyword in Java is used to prevent modification of classes, methods, or variables, making them non-changeable.
• 💡 The 'this' keyword refers to the current object instance, helping avoid confusion between instance variables and method parameters.

Q & A

What is a class in Java?

A class in Java is a blueprint or template that defines the properties (instance variables) and behaviors (methods) of objects.

What is an object in Java?

An object in Java is an instance of a class. It allows access to instance variables and methods and is created at runtime.

Which keyword is used to declare a class in Java?

The 'class' keyword is used to declare a class in Java.

What is the purpose of the 'new' keyword in Java?

The 'new' keyword is used to allocate memory dynamically for an object at runtime.

What is a constructor in Java?

A constructor in Java is a special method used to initialize objects. It can set default values for instance variables and is called automatically when an object is created.

What are the characteristics of a constructor in Java?

A constructor has the same name as the class, does not have a return type, and cannot be static or final.

What is the difference between a default constructor and a parameterized constructor?

A default constructor has no parameters and is provided automatically by the compiler if no constructors are defined. A parameterized constructor accepts arguments to initialize objects with specific values.

What is constructor overloading in Java?

Constructor overloading allows a class to have multiple constructors with different parameter lists, enabling the creation of objects with various initial conditions.

What is the role of the garbage collector in Java?

In Java, the garbage collector automatically deletes objects that are no longer in use and deallocates their memory, eliminating the need for destructors.

What is the use of the 'final' keyword in Java?

The 'final' keyword is used to make classes, variables, and methods unchangeable. A final variable can only be assigned once, a final method cannot be overridden, and a final class cannot be inherited.