Top 25 Java Interview Questions

Java is a widely-used programming language. Applications range from the Internet of Things (IoT) to Android apps, and Java was the most popular job title in 2019. Given its widespread use, it's no wonder that experts knowledgeable in Java continue to be in great demand.

Let us take a look at 25 Java interview questions:

1. What makes Java a platform-agnostic language?

Because the compiler compiles the code and then transforms it to a platform-independent bytecode that can be executed on different platforms, Java language was designed to be independent of any hardware or software. The sole need for running a byte code is that the system is equipped with a Java Runtime Environment (JRE).

2. In C/C++, pointers are used. Why is it that Java does not use pointers?

Beginner programmers should avoid using pointers since they are extremely complex. The use of pointers might make Java difficult since it focuses on code simplicity. The usage of a pointer might also lead to problems. Furthermore, when pointers are used, security is weakened since pointers allow people to directly access memory.

3. What is the main() method's significance in Java?

In Java, the main() function is the starting point for any application. In Java programming, the main function has the following syntax: public static void main (String args[]).

The main function is public and static. Java may access it without having to initialize the class. The value supplied in the input parameter is an array of Strings used to send runtime parameters.

4. Is Java a pass-by or a pass-by-reference language?

This is one of the most perplexing Java problems. Some feel it is a Pass-by reference, while others say it is Pass-by value. However, everything in Java is Pass-by Value, according to the Java Spec. Variable passing and method calling as method parameters are closely connected with these concepts. When we give a complex type reference as a method argument in Java, the memory address is transferred to a new reference variable in the same way.

5. What is the difference between the variable path and Classpath?

The path is an environment variable that operating systems use to find executable files. That is why, whether installing Java for the first time or wishing for an executable to be discovered by the operating system, we must include the directory path in the Path variable.

6. What exactly is an immutable object? Are you able to create immutable objects?

Immutable classes in Java are those whose objects can't be changed once they've been created. Any change to an immutable object creates a new object. In Java, for example, a String is immutable. Most immutable methods in Java are also final to prevent subclasses from overriding methods in Java, which might jeopardize immutability. You may achieve the same result by declaring members non-final but private and only changing them in the function Object() { [native code] }.

7. Is it possible for users to design their functional interface?

Yes, they can.

8. What's the connection between functional interfaces and Lambda expressions?

Lambda expressions are only used on the abstract method of the functional interface.

9. In the context of Java 8, what does the word "method reference" mean?

It is a concise Lambda expression technique.

10. What is the definition of stream pipelining?

The technique of chaining together multiple activities is known as stream pipelining. Pipelining does this by separating stream activities into two categories: intermediate and terminal processes. Each intermediary operation returns a stream instance when it completes. As a result, a user may create a processing pipeline by configuring an arbitrary number of intermediary actions to process data.

11. What is the difference between a Java path and a Classpath?

Path and Classpath are environment variables at the OS level. A path is used to designate where the system will look for executable (.exe) files, and a classpath is used to specify where the system will look for .class files.

12. In Java, what are local variables?

Local variables are variables declared within a code block, such as methods. Before accessing local variables, they should be initialized.

13. What is the main method's return type?

We may define the main method void since it does not return anything.

14. What is the main method's argument?

When it comes to arguments, the main method accepts an array of String objects.

15. What is inheritance, and how does it work?

Inheritance refers to the ability of one class to extend to another. For the coding to be reused from one class to the next, the existing class is referred to as a Superclass, while the derived class is referred to as a Subclass.

16. Is it possible to have an abstract class without any abstract methods?

Yes, abstract classes can exist without abstract methods.

17. What are the benefits of using static methods and variables?

We use a static keyword to make a method or a variable shared for all objects when we need to share a method or a variable among many objects of a class, rather than making separate copies for each object.

18. What exactly is a package?

A package is a grouping of related classes and interfaces. In a Java class, the package declaration should be the first statement.

19. Which packages do you have access to by default?

Even if you don't declare a package, the Java.lang package is foreign by default.

20. How can you get access to a private class outside of its package?

It's not possible.

21. In Java, how do you generate random numbers?

You may create random integers in the range of higher than or equal to 0.1 and less than 1.0 with Math. random()., using the Random class from Java. util package.

22. In Java, what is the basic class from which all other classes are derived?

java.lang.object

23. Is it possible for Java's main() function to return any data?

Because Java's main() function cannot return any data, it is always specified with a void return type.

24. How can we send a function an argument by reference rather than by value?

Only by value, not by reference, can we send arguments to a function in Java.

25. In Java, how is an object serialized?

The class serializable implements an interface called Serializable in Java to serialize an object into a byte stream. All objects in a class that implements the Serializable interface are serialized and stored in a byte stream.

Conclusion

Java is a well-known programming language among programmers. Its syntax is more straightforward, and it is supported by all operating systems, making it a viable option. Today, the Java programming language is used by over ten million developers, and Java has evolved significantly over time to provide more to its users.