Java Viva Questions and Answers
Question: Explain Java programming language.
Answer: It is a high-level programming language. This programming language is based on the principles of object-oriented programming. Large-scale applications can be developed by using this programming language. Also called the object-oriented programming language. It is platform independent language. In this modern software era, the Java programming language is the backbone of millions of software applications. Java is used in many real-world Java applications, including technologies and tools. This Java programming language has become the backbone for developing many applications. In areas like embedded systems and in enterprise solutions, this Java has made its mark. Almost three billion devices, irrespective of their operating systems like Android, UNIX, Mac OS, and Windows, use Java for development, according to Oracle.
Question: Explain some of the uses of Java programming language.
Answer: For most of the back-end development projects, this Java programming language is used as the server-side language. In these back-end development projects involving android development and also those involving big data, we use Java. In mobile computing, desktop computing and in numerical computing, Java is the most commonly used programming language. In game consoles, scientific supercomputers, cell phones, data centres and many other devices, Java is used. After C and python programming languages, Java is one of the third most popular programming languages in the world. Java is used widely because of its reliability and ease of use. For constructing applications on laptops, Java is used.
Question: Explain how Java is used in web-based programmes.
Answer: Java is also known as a server-side programming language. So, in Apache Hadoop, Hibernate, Spring and many others, it is often used for constructing web applications. Famous websites like LinkedIn, Amazon and many others use Java.
Question: Why Java programming language is known as platform independent language?
Answer: This programming language is developed in such a way that it does not depend on any hardware and also on software too. Java is known as platform independent language because of the fact that the compiler compiles the code. And this compiled code is then converted into platform-independent byte code. This code now runs on multiple systems. That's the reason Java is known as "write once run anywhere". For the machine to run this byte code, there is a condition that the machine should have a runtime environment (JRE) installed in it.
Question: Why is Java not a pure object-oriented language?
Answer: Java is not a pure object-oriented language because Java programming language uses primitive data types such as int, float, char, Boolean, short, long and double. Simply we can say that Java has direct access to primitive data types. These primitive data types do not belong to the integer classes directly. Primitive data types could be made as objects like strings by the developers. But the thing is, primitive data types such as float as int are much faster than the object. The developers kept primitive types in their language in order to achieve faster execution. Java is known as a 98% object-oriented language but not a pure object-oriented programming language. Because of the reason Java supports these primitive data types, it does not know as a pure object-oriented language. The reason is in the Java programming language, and everything will be underclasses.
Question: Why is this Java programming language highly suitable for mobile applications?
Answer: As Java is a powerful programming language and also a versatile programming language, it plays an important role in mobile development. This Java can be used for developing a wide range of mobile applications. Android Studio, which is a must for developing mobile applications, is developed by using Java and also it is the official integrated development environment (IDE) for the android platform. This Android Studio is based on IntelliJ IDEA, and this is written in Java and designed in a way to achieve maximum productivity with its powerful code editor. From memory leaks, this Java programming language safeguards the native code. In android development, this versatile programming language is used to compile different functionalities in each platform.
Question: Explain how Java is used in IoT.
Answer: For IoT – (Internet of Things) device development, most developers prefer Java as the best programming language. The main reason here to use it is because this programming language is platform agnostic. We create code only once, and this code operates on a wide variety of devices by reducing the overall workload for the programmers.
Question: Explain the differences between Java programming language and C++.
Answer:
- One of the main differences between Java and C++ programming languages is that Java is both compiled and interpreted programming language. In contrast, C++ is the only compiled language.
- If the Java program is once written, it can be run anywhere. Simply, we can say Java is a platform-independent language and also a machine-independent programming language. And Java can be compiled on every platform. In comparison, the C++ program can run only on the machine on which its compilation is done.
- C++ programming language requires manual memory management, and Java programming language memory management is system controlled.
- For system programming, mainly C++ language is used. And Java is widely used for application programming. Mostly, the Java programming language is widely used in Windows-based, mobile applications, in web-based applications.
- Java does not support the goto statement in it. In comparison, C++ supports goto statements to use in the programs.
- Java does not support operator overloading. But C++ programming language supports operator overloading.
- Multiple inheritance is supported in C++. Java does not support multiple inheritance. But there is another way to achieve multiple inheritance in Java by using interfaces.
- Call by value and call by reference were both supported by the C++ programming language. Whereas Java does not support the call by reference, and it only supports the call by value in its programs.
- Documentation comment is not supported by the C++ programming language. In contrast, Java programming language supports documentation comments. And these documentation comments are used to create documentation for Java source code.
- Default arguments were supported by the C++ programming language. But Java does not support default arguments.
- Header files were not supported by the Java programming language. But C++ supports header files.
- The virtual keyword will not be there in Java. In C++ programming language, we use virtual keywords in the programs.
- In a Java programming language, we have a garbage collector. But in C++, we do not have a garbage collector.
- Java does not support pointers in its programs. Whereas in C++ programming language, we will have pointers, and we use the pointers when we are writing the program.
- We do not have global variables in the Java programming language. In C++, we will have global variables in its programs.
- Template class will be there in C++. But in the Java programming language, we do not have a template class in its programs.
- One of the other main differences between Java and C++ programming languages is in Java, and we will have packages and interfaces. But in the C++ programming language, we do not have packages and interfaces.
- We do not have API in C++. We have API in the Java programming language.
- There will be a pretty consistent between primitive data types and object types in C++ programming language. But in the Java programming language, semantics differs between object types and primitive data types.
- Both namespace scopes and global scopes were supported by C++. Java does not support global scope in its programs.
- When it comes to access control and object protection, a flexible model with constant protection is available in C++ programming language. Java encourages weak encapsulation, and in the Java programming language, the model is cumbersome.
Question: Explain the similarities between Java and C++.
Answer:
The similarities between Java and C++ programming languages.
- With both C++ and Java programming languages, we have vast areas of applications.
Like using C++ programming languages, MYSQL is written, and C++ is mostly and also majorly used in game development. Popular applications like Adobe Premiere, Illustrator and a few others were scripted by using C++ programming language only. High-performance image processing is done by using this C++. Also widely used in many advanced types of medical equipment. Cluster data processing, File system and also Google chromium browser file all are in using the C++ programming language. Large software is developed by using this programming language, and it is suitable for it.
As Java is a versatile programming language and also a powerful programming language, it is used in a wide variety of software applications in most software fields all over the world. Mainly Java is used in mobile and also in android application development. Java is also used in network applications and Web app development. For running large enterprise software, Java enterprise Edition provides an API and also a runtime environment. Desktop GUI applications were developed using the Java programming language. Applications developed by Java programming language embedded in the highly used technologies like disk players, TV and also mainly in SIM cards which we use in mobile phones.
- In both programming languages, abstraction is there.
- In both C++ and Java programming languages, encapsulation is there.
- Single inheritance will be there in both languages. But when it comes to multiple inheritance it will be there in C++ but not in the Java programming language, but it can be achieved by some other method in Java, but not directly.
- In both programming languages, polymorphism is possible.
- Static binding is there in both C++ and also in Java.
- Dynamic binding, too, is there both the programming languages.
- For both programming languages, the syntax is almost similar.
- Comments like single-line comments and also multiple-line comments are written in the same in both programming languages.
- Conditional statements like if statement, if-else statement, nested if, else if, and switch statements are similar in both programming languages.
- Loops like the while loop and for loop (Simple for loop and nested for loop) are similar in both the C++ programming language and also in the Java programming language.
- Operators like relational operators and arithmetic operators are the same in both programming languages.
- In both C++ and in Java programming languages, the execution of the programs written starts from the main function only. (The only difference is main function declaration is different in C++ and Java, but the name is the same.)
- In both programming languages, the statements written in the program will end with a semicolon only. (;)
- Primitive data types like int, float, double, long, short, Boolean, and char are similar in both C++ and Java programming languages.
But the Boolean value in C++ is called bool, and in the Java programming language, it is called a Boolean value.
- Keywords like public, private and protected are the same in both programming languages. And those keywords are known as access specifiers.
- Other most used keywords like static, return, new, double, break, continue, and char are similar in both C++ and Java programming languages.
- One of the important concepts of multi-threading is supported by both Java and C++ programming languages.
These programming languages allow us to execute multiple threads concurrently, and by this execution, one can achieve multitasking.
Question: Explain the difference between stack memory and heap memory in Java.
Answer:
Stack Memory: As the name indicates, static memory is the memory in a Java programming language which is used for static memory allocation. And also, this static memory is used for the execution of the threads. For a class, when an object has been created, the reference of the object will contain in stack memory, and this object will always be stored in heap memory. For each object created separate stack will be get created by this stack memory. Automatically stack allocation will be done by the operating system which we are using when a thread is created. It is not used by all parts of the application, and this stack memory is used only by one thread of execution. For each thread, at run time, this stack memory will be get allocated, and this stack memory is a physical space in Random Access Memory (RAM). This stack memory follows LIFO (Last In First Out) for accessing the memory. Simply we can say that memory management follows LIFO (Last In First Out). To the owner thread, only the variables are visible in this stack memory. This stack memory is mainly used to store the local variables and to store the order of method execution. Memory allocation in this stack memory is continuous allocation. When the thread is created, this memory will be get created. It was accessible globally. A separate stack for each thread will be created by Java Virtual Machine (JVM). We cannot alter the allocated memory once it is done. This stack memory is not flexible like heap memory. Allocation and deallocation are faster in this stack memory. Faster access will be there in this memory type. Memory size is similar in this memory. Another important thing is we can increase the size of the stack by using the JVM option -Xss. Java.lang.StackOverFlowError will be get thrown automatically whenever the stack size is greater than the limit it allocated. So to avoid this error, only we increase the size of the stack by using the JVM option -Xss. The advantage of using this memory is the cost will be less when compared to heap memory, and it is affordable. But the implementation of the stack memory is hard. Using this stack memory, we can say it is threaded safe because for every thread created, there will be its own stack for every thread.
Heap Memory: Heap memory is also known as dynamic memory; it is the area memory in which objects get stored. Memory block allocation and deallocation are not done in a fixed pattern. Simply, we can say the allocation of memory is done randomly. Implementation of heap memory is easy, but the cost of this memory is more when compared to stack memory. This memory is shared among all threads. Heap memory will be created when the Java Virtual Machine starts running. As long as the application is running, the heap which is created is shared between the threads of the objects. For local stack memory, heap memory is the alternative stack memory. In heap memory, automatically, local variables are allocated when a function is called. As the function exits, deallocation of the local variables is done automatically. The size of the heap memory is larger when compared to stack memory. Allocation and deallocation are slower. Also, the access is slower than stack memory. As we can alter the memory, this heap memory is flexible. JRE (Java Runtime Environment) classes and also objects are stored in this memory. As the alternative indicates, this memory does not follow any order. The memory allocation is done dynamically. -Xmx and -Xms JVM options are used to increase or decrease the size of the heap memory. In stack memory, we can increase the size of the stack, but here we can increase or decrease the size of the heap memory. Visible to all threads. Java.lang.OutOfMemoryError will be thrown by the Java Virtual machine, and this exception arises when Java Virtual Machine is unable to create a new native method. Allocation and deallocation are done by the programmer in heap memory. As stack memory, this heap memory is not thread-safe. The code which is properly synchronized is required.
Question: Why does Java not make use of pointers as they are used in C and C++ programming languages?
Answer: As a beginner programmer, it is not that good and safe to use pointers. Because the reason is they are quite complicated, and their usage of them in the code makes the code complicated and challenging to the programmer. The main of the Java programming language is to make code simple but not complicated. Potential errors can be caused by using these pointers utilization in the program. If we use pointers in the program, the user can directly access the memory with the help of these pointers. So, when we use pointers in the program, we have to compromise the security of the access, and here security issues arise because of the usage of pointers. To reduce the usage of memory spaces, the Java programming language does not make use of the concept of this pointer in its programs, and the reason is these pointers take more time at the run time and also occupy more memory space at the run time. We can say that overall, this Java programming language does not have and also it does not support the concept of the pointer. The usage of pointers in the programs makes robustness and makes the programming language hard to understand and makes it complex too. So, this Java uses the idea of references in it instead of using pointers in its language. So, in the Java programming language, these pointers are called references. And the use of these references is much more than using of pointers. Pointer has the null value, but the references do not.
Question: Explain instance variables in Java.
Answer: Instance Variables: Instance variables can be said as non-static variables in Java. These instance variables are defined in a class but outside of any methods, blocks or also in constructors.
As we know that whenever a class is defined, its instance will be created. And that instance is known as an object. We say a class is instantiated if and only if its object (its instance) is created. And also, these instance variables are accessible to all the methods, blocks, and to constructors.
In the most simplified way, we can see that the instance variables are the variables outside of any method, but they are a must in a class.
We can declare instance variables by using different types of access modifiers available in a Java programming language like private, public, default and protected.
When an object of the class is created or at the time of class loading, initialization of the instance variable is done.
Let us take an example program to understand the instance variables.
public class AtheleteGame {
public String athleteFullName;
public double athleteSpeedPerHour;
public int athleteAge;
public int athleteIdNumber;
public AthleteGame (name, speed, age, id) {
this.athleteFullName = name;
this.athleteSpeedPerHour = speed;
this.athleteAge = age;
this.athleteIdNumber = id;
}
public void athleteRuns() {
double speed = 200;
String name = “Usha”;
int age = 30;
int id = 234;
system.out.println(“Athlete Name is” + name + “.”);
system.out.println(“Athlete speed is”+ speed + “km/hr in the given target”);
system.out.println(“Athlete age is” + age + “currently”);
system.out.println(“Athlete id is” + id + “in the group);
}
}
In the program athleteFullName, athleteSpeedPerHour, athleteAge, and, athleteIdNumber are the instance variables.
Question: Explain the default values of instances and variables in the Java programming language.
Answer:
- For variables, there will be no default values.
- In Java, we have to initialize values for them before using variables.
- If we do not initialize variables and we use them in the program, they will throw a compilation error when we execute the program.
- When it comes to instances in the Java programming language, the default constructor in the program will assign the default value for the instance when we create an object for it.
- Depending upon the data type, the default value will be get assigned.
- The null value will be get assigned if it is a reference.
- The “zero” will be assigned if the instance variable is numeric type.
- "False" will be get assigned if it is a Boolean type.
Question: Can we overload static methods?
Answer: With different input parameters and with the same name, we can overload the static method in the Java programming language. So, the answer is yes, and we can overload the static methods. There can be two or more static methods in the program.
Question: Can we override the static methods in a Java programming language?
Answer: The answer is no; we cannot override the static methods in the Java programming language.
The reason is the run time polymorphism will not take place in the case when the declaration of static methods having the same signature is made in the subclass.
As we know that dynamic polymorphism, which is also called overriding, will occur at the runtime.
And these static methods are looked up at the compile time statically. So, that is the reason that we cannot override the static methods in the Java programming language.
Question: Explain shallow and deep copy in the Java programming language.
Answer: Shallow copy and deep copy are some of the methods in several methods which are used to copy the object’s data.
Shallow Copy: This method will create a new reference. And points to the same object which is already written.
Deep Copy: Unlike the shallow copy in this method, we create a new object directly. But, in shallow copy, we create a new reference instead of a new object. Here, in deep, copy the old object value to the created new object.
Question: Explain the main objective of garbage collection in the Java programming language.
Answer: The memory space which is occupied by the objects which are unreachable and unnecessary gets freed up by this garbage collector. This process is done by the garbage collector at the time of execution by deleting unreachable and unnecessary objects.
Question: Explain static methods in the Java programming language.
Answer: If we declare any method using the keyword static, then the method is called a static method.This static method belongs to the class of the program. For the static methods, when the class is loaded, it gets memory. But this method does not belong to the object of the class. For static methods, they have access to the static variables. If we take the example of the static method, the main () method is the most common example. We can call these static methods without creating an object in the class because they can be directly called when by the classes in the program.
Question: Explain static classes in the Java programming language.
Answer: The important thing about the static classes is in the Java programming language, the classes cannot be static as static variables and static methods. But if the class is the inner class, then it can be a static class. The static class will work exactly like the static members of the class if it is the static inner class.
Question: What is data encapsulation?
Answer: It is one of the object-oriented programming concepts. It is the concept of hiding data attributes as we know that in this Java object-oriented programming language, these data and code are getting associated with the objects of the classes. Also, encapsulation can be defined as the process which combines code and data into a single unit. To implement this encapsulation, Java uses the concept of class.
Question: Explain abstraction in the Java programming language.
Answer: It is also one of the object-oriented programming concepts in the Java programming language. This abstraction does not show the actual things to the end user mainly. The main objective of this concept in object-oriented languages is to hide the details which are internal, and it shows only essential functionality to the user. And shows only the things that the user needs to know.