Advanced java interview questions

Java is an all-time favourite programming language in the world. According to the latest research, 90% of Fortune 500 companies use Java, and almost all Android apps are based on Java programming, with 9 million Java developers placed all around the world. And if you are a developer and searching for job, then you need these questions that will help you crack advanced Java interview questions.

These questions are definitely there for your interview. And if you get these questions, then they will definitely help you with advanced Java interview questions in the future.

Q1: How does Garbage Collection prevent a Java application from going out of memory?

Answer

It doesn’t! Garbage Collection simply cleans up unused memory when an object goes out of scope and is no longer needed. However, an application could create a huge number of large objects that cause an OutOfMemoryError.

Q2: What differences exist between HashMap and Hashtable?

Answer

There are several differences between HashMap and Hashtable in Java:

1. Hashtable is synchronised, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronised ones.
2. Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values.
3. One of HashMap’s subclasses is LinkedHashMap, so in the event that you’d want predictable iteration order (which is insertion order by default), you could easily swap out the HashMap for a LinkedHashMap. This wouldn’t be as easy if you were using Hashtable.

Q3: What are function overriding and overloading in Java?

Answer

• Method overloading in Java occurs when two or more methods in the same class have the exact same name, but different parameters.

class Dog{

    public void bark(){

        System.out.println(“woof “);

    }

 

    //overloading method

    public void bark(int num){

     for(int i=0; i<num; i++)

     System.out.println(“woof “);

    }

}

• On the other hand, method overriding is defined as the case when a child class redefines the same method as a parent class. Overridden methods must have the same name, argument list, and return type. The overriding method may not limit the access of the method it overrides.

class Dog{

    public void bark(){

        System.out.println(“woof “);

    }

}

class Hound extends Dog{

    public void sniff(){

        System.out.println(“sniff “);

    }

 

    public void bark(){

        System.out.println(“bowl”);

    }

}

 

public class OverridingTest{

    public static void main(String [] args){

        Dog dog = new Hound();

        dog.bark();

    }

}

Q4: What is reflection, and why is it useful?

Answer

The name reflection is used to describe code which is able to inspect other code in the same system (or itself) and to make modifications at runtime.

For example, say you have an object of an unknown type in Java, and you would like to call a ‘doSomething’ method on it if one exists. Java’s static typing system isn’t really designed to support this unless the object conforms to a known interface, but using reflection, your code can look at the object and find out if it has a method called ‘doSomething’ and then call it if you want to.

Method method = foo.getClass().getMethod(“doSomething”, null);

method.invoke(foo, null);

Q5: What is the difference between an exception and an error in Java?

Answer

• An Error “indicates serious problems that a reasonable application should not try to catch.”
• An Exception “indicates conditions that a reasonable application might want to catch.”

Q6: What is the difference between an Interface and an Abstract class?

Answer

Java provides and supports the creation of both abstract classes and interfaces. Both implementations share some common characteristics, but they differ in the following features:

• All methods in an interface are implicitly abstract. On the other hand, an abstract class may contain both abstract and non-abstract methods.
• A class may implement a number of interfaces but can extend only one abstract class.
• In order for a class to implement an interface, it must implement all its declared methods. However, a class may not implement all the declared methods of an abstract class. Though, in this case, the sub-class must also be declared as abstract.
• Abstract classes can implement interfaces without even providing the implementation of interface methods.
• Variables declared in a Java interface are by default final. An abstract class may contain non-final variables.
• Members of a Java interface are public by default. A member of an abstract class can either be private, protected, or public.
• An interface is absolutely abstract and cannot be instantiated. An abstract class also cannot be instantiated but can be invoked if it contains a main method.

Q7: Can == be used on enum?

Answer

Yes: enums have tight instance controls that allow you to use == to compare instances. Here’s the guarantee provided by the language specification.

Q8: How can I synchronise two Java processes?

Answer

It is not possible to do something like you want in Java. Different Java applications will use different JVM’s, fully separating themselves into different ‘blackbox’es. However, you have two options:

• Use sockets (or channels). Basically, one application will open the listening socket and start waiting until it receives some signal. The other application will connect there and send signals when it had completed something. I’d say this is a preferred method used in 99.9% of applications.
• You can call Winapi from Java (on Windows).

Q9: Is Java pass-by-reference or pass-by-value?

Answer

Java is always pass-by-value. Unfortunately, when we pass the value of an object, we are passing the reference to it. There is no such thing as “pass-by-reference” in Java. This is confusing to beginners.

The key to understanding this is that something like

Dog myDog;

is not a dog; it’s actually a pointer to a dog.

So when you have

Dog myDog = new Dog(“Rover”);

foo(myDog);

you’re essentially passing the address of the created Dog object to the foo method.

Q10: Is there anything like static class in Java?

Answer

Java has no way of making a top-level class static but you can simulate a static class like this:

• Declare your class final. – Prevents extension of the class since extending a static class makes no sense
• Make the constructor private. – Prevents instantiation by client code, as it makes no sense to instantiate a static class
• Make all the members and functions of the class static – Since the class cannot be instantiated, no instance methods can be called or instance fields can be accessed
• Note that the compiler will not prevent you from declaring an instance (non-static) member. The issue will only show up if you attempt to call the instance member

How person get help with these advanced java interview questions

Advanced Java interview questions can help a person in many different ways.

 

Preparing for technical interviews: Advanced Java interview questions are frequently asked technically for senior or specialised roles. Familiarity with these questions boosts applicants’ confidence during the interview process.

 

Demonstrating in-depth knowledge: Advanced Java questions measure a candidate’s grasp of advanced Java programming principles and capabilities. Answering these questions effectively displays a strong mastery of Java, which improves the candidate’s profile and helps you crack advanced java interview questions

 

Highlighting problem-solving abilities: Many advanced Java problems include challenging problem-solving scenarios. Answering these questions displays not just technical knowledge but also a candidate’s ability to approach and solve complex challenges.

 

why advanced Java interview questions asked? 

Advanced Java interview questions measure applicants’ grasp of Java concepts beyond their basic knowledge. They test proficiency in things such as multithreading, collections, design patterns, and frameworks to make sure candidates are comfortable with the modern technologies needed for challenging application development.  To ensure about candidate interviewer commonly ask these advanced Java interview questions,

We hope these advanced java interview questions will help you, to clear your interview, and these advanced java interview questions will also help you with your future projects.