Java Interview Question (Hard)

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Questions and Answers

Which type of constructor is created by the compiler when no constructor is defined in the program?

Default constructors (correct)

Parameterized constructors

Static constructors

Private constructors

Can a constructor be invoked without creating an object?

Yes, a constructor can be invoked without creating an object

Yes, a constructor can be invoked using the 'new' keyword

No, a constructor cannot be invoked directly (correct)

No, a constructor can only be invoked after creating an object

Can a constructor of a superclass be inherited by a subclass?

No, a constructor of a superclass cannot be inherited by a subclass (correct)

Yes, a constructor of a superclass can be inherited by a subclass

Yes, a constructor of a superclass can be overridden by a subclass

No, a constructor of a superclass cannot be accessed by a subclass

What is the difference between constructors and methods?

Constructors are invoked when a class is instantiated, while methods are invoked to perform specific tasks Signup and view all the answers

Which one of the following best describes the purpose of the JVM (Java Virtual Machine)?

To verify and execute Java programs Signup and view all the answers

What makes Java a platform-independent language?

Java code is converted into an intermediate Bytecode language Signup and view all the answers

Which keyword is used to eliminate the confusion of multiple methods of the same name existing in the program?

this Signup and view all the answers

What is the purpose of the JIT (Just In Time) compiler in Java?

To optimize and run Java code in the least possible time Signup and view all the answers

What is constructor chaining?

Calling a constructor from the same class using another constructor Signup and view all the answers

What is the accessibility of a class with the 'protected' access modifier in Java?

Accessible within the current package and through a child class Signup and view all the answers

How is constructor chaining achieved?

By using the 'this' keyword for the constructor in the same class Signup and view all the answers

Why are pointers not supported in Java?

To achieve security by abstraction Signup and view all the answers

Which one of these is an example of multi-level inheritance?

Class A extends Class B and Class C extends Class B Signup and view all the answers

Which one of these is an example of hierarchical inheritance?

Class A extends Class B and Class B extends Class C Signup and view all the answers

Which one of these is an example of hybrid inheritance?

Class A extends Class B and Class A extends Class C Signup and view all the answers

Which one of these is an example of method overriding?

void show() { System.out.println("method2"); } Signup and view all the answers

Which method can be declared final in Java?

Most methods Signup and view all the answers

Can an interface be declared final in Java?

No Signup and view all the answers

What is static binding in Java?

Identifying classes and objects during compile time Signup and view all the answers

What is dynamic binding in Java?

Identifying classes and objects during run time Signup and view all the answers

What does the InstanceOf operator do in Java?

Checks if an object is an instance of a class or subclass Signup and view all the answers

What is a multithreaded program in Java?

A program that uses multiple threads Signup and view all the answers

Which one of the following is the correct definition of encapsulation in Java?

Encapsulation is a way to wrap variables and methods in a single block. Signup and view all the answers

Which one of the following is the correct definition of polymorphism in Java?

Polymorphism occurs when multiple child classes inherit the methods of a parent class. Signup and view all the answers

Which one of the following is the correct definition of abstraction in Java?

Abstraction is used to hide unwanted or unnecessary information. Signup and view all the answers

Which one of the following is the correct definition of inheritance in Java?

Inheritance is when one class acquires the properties of another class. Signup and view all the answers

Q1. What is the purpose of JDK in Java development?

JDK is used to compile Java programs Signup and view all the answers

Q2. What is the purpose of Javac in Java development?

Javac is used to compile Java programs Signup and view all the answers

Q3. What are some major features of Java?

Java is an object-oriented programming language Signup and view all the answers

Q4. What is the difference between JDK and JRE?

JDK is used for development, while JRE is used for runtime Signup and view all the answers

Study Notes

Constructors

If no constructor is defined in a program, the compiler creates a default no-argument constructor.
A constructor cannot be invoked without creating an object.
A subclass does not inherit a constructor from its superclass.
The key differences between constructors and methods are:
Constructors do not have a return type, not even void.
Constructors are called only once during object creation.
Constructors have the same name as the class.

Java Platform

The JVM (Java Virtual Machine) is responsible for executing Java bytecode on different platforms.
Java is a platform-independent language because the JVM translates Java bytecode into machine-specific code.
The 'overload' keyword is used to eliminate confusion between multiple methods of the same name.

Access Modifiers

A class with the 'protected' access modifier is accessible within its class, its subclasses, and in the same package.

Inheritance

Constructor chaining is the process of calling one constructor from another constructor in the same class or its superclass.
Constructor chaining is achieved using the 'this' and 'super' keywords.
Pointers are not supported in Java for security and memory management reasons.

Inheritance Examples

A class inheriting from two classes is an example of multi-level inheritance.
A class inheriting from a class that itself inherits from another class is an example of hierarchical inheritance.
A combination of multi-level and hierarchical inheritance is an example of hybrid inheritance.
A subclass providing a specific implementation of a method already provided by its superclass is an example of method overriding.

Methods and Variables

A final method cannot be overridden in a subclass.
An interface cannot be declared final in Java.
Static binding in Java is a process where the method to be called is determined at compile-time.
Dynamic binding in Java is a process where the method to be called is determined at runtime.
The 'instanceof' operator checks if an object is an instance of a particular class or subclass.

Multithreading and Encapsulation

A multithreaded program in Java is a program that can execute multiple threads concurrently.
Encapsulation is a concept where an object's state is hidden from external interference and misuse.
Abstraction in Java is the concept of showing only essential features of an object or system.
Inheritance in Java is the process of creating a new class based on an existing class.
Polymorphism in Java is the concept of an object taking on multiple forms.

Java Development Kits and Tools

The JDK (Java Development Kit) is a software development kit that provides tools and libraries for Java development.
The Javac compiler is used to compile Java source code into bytecode.
Major features of Java include platform independence, object-oriented programming, and multithreading.
The JDK includes the JRE (Java Runtime Environment) and development tools, whereas the JRE is a part of the JDK that provides a runtime environment for executing Java bytecode.

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Description

Test your knowledge on object-oriented programming concepts and keywords with this quiz. Explore topics such as inheritance, encapsulation, and the super keyword. Perfect for interview preparation or brushing up on your OOP skills.