Advanced Java Interview Questions

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Introduction

One of the most difficult languages available now is Java. The number of people working on the Java programming language is actually 10 million, however, it is rising daily. So, if you're a Java developer, an aspiring Java developer, or a student of computer science, you'll probably go to a Java interview or viva exam. Interviewers frequently assess your programming expertise by asking Advanced Java questions.

1. What Function does Java's garbage collection serve?

When an object is no longer required by the program or is idly using program resources that could be released and used by other objects, it is identified and removed using Java's trash collection feature. When a Java Program in which it is executed no longer has access to an object, it gets garbage collected.

2. What are Lambda Expressions?

A new feature of Java 8 is lambda expressions, sometimes known as lambdas. They give programmers a simpler way to work with interfaces that only have one method, and they are frequently utilized in cases where anonymous classes are employed.

When all we care about is publishing any sentence, there are occasions when we need to write multiple lines in order to accomplish our goals. A lambda expression allows us to accomplish this in a single line. Consequently, lowering the number of lines of code will increase the program's effectiveness.

3. What does a Java Thread mean to you?

Each process may have two or more "Threads," each of which represents a single sequential flow of control. The java.lang package in Java creates and manages threads. thread type.

There is at least one thread in each Java process or application (also known as the main thread). A process may have many threads to handle different duties, such as memory management and 1/0, depending on the demands of the programmer.

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4. Why would we want to use Multiple Threads in our Application? Why not just stick to the main Thread?

There are two main reasons:

First, sometimes we want to perform a task that will take a long time. For example, we may want to query a database, or we may want to retrieve data from somewhere on the Internet. We could do this in the main thread, but the code in each main thread is executed linearly. The main thread will not be able to do anything else while waiting for data.

This can also be expressed as a suspension of the main thread's execution. The following line of code cannot be executed before the data has been returned. Particularly when working with a UI application, it could look to the user as though our application crashes or freezes.

As a result, we can construct many threads and do a lengthy task on each of them rather than causing the main thread to become blocked. This would allow the main thread to carry on with its work. This process is called multithreading. It can report progress or receive user input while a long-running task continues in the background.

5. When and how does a Deadlock occur in any Program?

When two or more threads are blocked by locks and one thread is holding a lock that another thread needs, a deadlock results. For instance, thread 1 holds lock 1 while awaiting the acquisition of lock 2, whereas thread 2 holds lock 2 while awaiting the acquisition of lock 1. All threads holding the locks are subsequently blocked as a result of this. As a result, none of the waiting threads ever start since it never releases the locks it is holding. 

6. Why do Developers use BufferedReader to read any file in Java?

A BufferedReader reads text from an input stream and stores the characters in a character array. Reading chunks of data from a stream (as opposed to a file) is more efficient than reading multiple characters at once.

Therefore, we can state that BufferReader is more efficient and faster. We can also specify the buffer size, but the default value is 8 KB, which is sufficient for most purposes.

7. Define Java nio.

A new I/O package called Java was introduced to the Java SDK.nio with Java 1.4. The classes in the package implemented 1/0 in a non-blocking manner, leading to the package's introduction as a Java I/O extension. Using Java.io classes to interact with the file system may have caused some developers to run into problems, which is why the Java.nio package was created.

8. Define JDBC Drivers?

A Java library that contains classes that implement the JDBC API is known as a driver. The interfaces that all JDBC drivers must implement make it simple for applications to switch their data sources. For instance, we can simply use the MySQL JDBC driver rather than the SQLite driver if the application utilizes an SQLite database and we subsequently decide that we want to use a MySQL database (except for migrating the data to the MySQL DB, of course).

Two packages make up JDBC: Java.sql (the basic JDBC package) and Javax.sql (optional JDBC). Working with database servers requires the Javax.sql package's APIs. Later, we'll talk about those. All well-known databases come with JDBC drivers. The JDK comes with a derby database that can be used for desktop applications or prototyping. The derby JDBC driver is also included in the JDK.

9. Describe the Benefits and Drawbacks of utilizing Java Sockets

Java Sockets' benefits include: Java uses sockets because of their adaptability and simple connection protocols. Additionally, they generate little network traffic, such as HTML forms and CGI scripts that construct and send entire web pages in response to each new data request.

Java Sockets' drawbacks include: The restriction of communication to the transmission of raw data packets between applications.

10. What do you mean by Synchronization? How does this benefit Multithreading?

Synchronization in multithreading regulates how many threads have access to shared resources. We can synchronize statements and methods in Java. Only one thread can run concurrently when any method in a Java application is synchronized. All other threads that seek to perform the same method or any other synchronized method started in the same class will therefore be suspended until the running thread has finished executing.

11. How does the "new" operator differ from the "newInstance()" operator in Java?

To construct objects, use the 'new' and 'newInstance()' operators. The distinction is that when we already know the class name for which we need to construct the object, we use the new operator. However, what if we don't know the class name for which we need to generate the object? What if we acquire the class name from a command line argument? What if we get it from a database? The "newInstance()" operator is then employed in this situation.

The "newInstance()" keyword throws an exception we need to handle. This is because there is a chance that the class definition does not exist, and we are getting the class name from the runtime. So it throws an exception.

12. Is it possible to exceed the memory limit in the program even though it has a garbage collector?

Yes, a program can run out of memory despite the presence of a garbage collector. Garbage collection helps identify and eliminate objects that are no longer required by the program to free up the resources they use.

If the object is unreachable in the program, garbage collection will be performed regarding this object. If the amount of memory needed to create a new object is insufficient, then memory is freed for objects no longer in scope using the garbage collector. A program's memory limit is exceeded when the freed memory is not enough to create new objects.

Additionally, heap exhaustion occurs when objects are created to remain in scope and consume memory. The developer should dereference the object after completing its work. Although the garbage collector tries its best to reclaim memory, memory limits may still be exceeded.

13. Define System.out.println()

System.out.println() prints a message to the console. 

The system is a class that can be found in java.lang package. The static variable Out belongs to the PrintStream class and is a part of the System class. A function called println() can be found in the PrintStream class.

So, if we justify the statement, we can say that if we want to print anything to the console, we have to call the println() method that was present in the PrintStream class. And we can call it using the output object present in the System class.

14. Can you explain the Life Cycle of a Java Thread?

The life cycle of a Java thread is as follows:

New: When a thread is instantiated, and the start() method has not been called, the thread is considered active and thus in the NEW state.

Runnable: Once the start() method is called before the JVM calls the run() method, the thread is said to be in the RUNNABLE state (ready to run). The thread's waiting or sleeping status can likewise be used to enter this state.

Running: When the run() method has been called, and the thread runs, it is said to be in the RUNNING state.

Non-Runnable (Blocked/Waiting): When a thread cannot run even though it is active, it is said to be in a NON-RUNNABLE state. Ideally, a thread should transition to a runnable state after some time in its lifetime. If a thread tries to enter synchronized code but is prevented from doing so because another thread is working on the same object in the synchronized block, it is said to be in the blocked state. When the second thread leaves the synchronized block, the first thread must wait. When a thread is waiting for a signal from another thread to execute, or when it is postponing work until it receives the signal, it is said to be in the waiting state.

Terminated: The thread is said to enter the TERMINATED step and is regarded as inactive when the run() method's execution is complete.

Conclusion

One of the straightforward high-level languages, Java offers the robust tools and outstanding standards required for application development. It was also among the first Programming Languages to offer outstanding threading support for dealing with concurrency-based issues. The key factors influencing Java's ever-increasing adoption in the software industry are its simple syntax and built-in capabilities, as well as the stability it offers to programs.

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