20 Java Interview Questions and Answers

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Are you looking for a web design job or any IT work associated with Java? If that is the case, we have compiled some of the common questions interviewers are likely to ask you with regards to the famed Java programming language. Java has quite some applications in the programming niche today ranging from the creation of apps, web designing and the creation of solution-oriented programs. In this article, you will find the top 20 java interview questions to prep you for your interview.

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Question 1: Briefly describe Java as a programming language

Java is a high-level programming language which was originally established by Sun Microsystems. It can run on a broad range of platforms which include iOS for Mac, Windows and several versions of the UNIX operating system such as Ubuntu, Sun Solaris, or Redhat, to name a few. The Java language was released in 1995. Some of the Java features include Object oriented, Platform Independent, multithreaded, robust, and interpreted.

Question 2: Why is Java referred to as dynamic?

Java has been designed to adapt to the ever-evolving programming environment. Therefore, programs written in Java can hold a broad range of run-time information that you can use to verify and resolve the accessibility of objects in a given run-time.

Question 3: What do JDK, JRE, and JVM acronyms mean, and what are their differences?

JVM stands for Java Virtual Machine and is an abstract machine that provides a runtime environment on which the Java bytecodes can be executed. It gives Java its platform-independent feature because the Java Virtual Machines are available for a variety of hardware and software platforms.

JRE, on the other hand, stands for the Java Runtime Environment. It provides the environment on which Java programs are run, therefore, can be referred to as the implementation of the Java Virtual Machine.

JDK is the Java development kit. It is where the Java applications are designed and exists physically. The package contains the Java Runtime Environment in addition to the several development tools available.

Question 4: What is implied by the term platform-independence with regards to Java?

It means that you can write and compile a java program in one platform like Mac OS for instance and at the same time run it on another platform like Windows. During the compilation of Java, it is not compiled into a platform-specific virtual machine but instead into bytecode that isn?t dependant on any platform. Therefore, the bytecode can be distributed throughout the internet making it able to be interpreted by several JVM running on whichever platform.

Question 5: What are the memory areas allocated by JVM?

JVM allocates many types of memory areas which include the class or method area, the heap, stack, program counter register and the native method stack.

Question 6: What is a class and what variables can it contain?

The class is the plan on which individual objects are developed. It includes fields and methods that can be used to describe how objects behave. The variables of a class include local variables, instance variables, and class variables. Local variables are those that are defined inside methods and blocks. The instance variables, on the other hand, are those within the class but outside the method. The class variables are declared with the static keyword and are usually within a class and outside the methods.

Question 7: Differentiate between a constructor and a method.

A constructor is used to initialize the state of the object within a class while a method exposes the behavior of an object.

The object is a regular member function of a class and usually, has a name that can also be void. The ‘constructor’ and the ‘method’ differ in the sense that the former is invoked by the new operator while the dot operator invokes the latter.

Question 8: Define the JIT compiler.

JIT stands for the Just-In-Time compiler which is a tool that improves the performance in Java. It plays a role of compiling parts of the bytecode which has the same compiling functionality. Consequently, this saves the time that could have been used for the compilation.

Question 9: What is the significant difference between Java Platform from the other platforms?

The Java platform, unlike the other platforms, is a software-based platform which runs on other hardware-based platforms. It constitutes of two components which are:
? Run-time Environment
? Application Programming Interface

Question 9: What is a class loader?

A class loader in Java is a subsystem of Java Virtual Machine that is used to load classes and interfaces. The various types of class loaders available in Java include the Bootstrap class loader, system class loader, and plugin class loader among others.

Question 10: What is the importance of garbage collection in Java?

Garbage collection involves identifying and discarding objects that are no longer under use so that their resources are let free for other purposes. That happens when the program executing the object can no longer reach it.

Question 11: Outline the steps for creating an object for a class.

Creation of an object involves three stages which are the declaration processes, instantiation, and initialization.

Question 12: When is the byte data type used in Java?

The byte data type is usually used to preserve space in vast arrays, usually in place of integers. That is applicable in because a byte is four times smaller than an integer.

Question 13: What role does the default constructor play in Java?

The Java default constructor provides values for the object by default especially when there is no constructor in the class. Java constructor is usually invoked at the time of object creation.

Question 14: What does the static variable entail?

It often refers to the common property for each object, for instance, the name of staff members within a given institution. During the class loading, a static variable is allocated memory only one in the class area.

Question 15: what are immutable classes, and can they be written?

Immutable classes in Java are those classes where the object cannot be altered once it has been created. When an immutable object is modified, it results in the creation of a new object.

Question 16: What is Singleton?

A singleton is a class which has only one instance in the entire Java application. An example is the java.lang.Runtime.

Question 17: Why is the main method static?

That is because the object is not needed to invoke the static method. Making the main method static would mean more memory allocation since Java virtual machine first creates the object then invokes the main () method afterward. You can get more information on this?here.

Question 18: Is it possible to execute a program without the main () method?

It is a yes. The static block procedure is one way of doing it. Other details are outlined on this?site.

Question 19: What is a composition as used in Java?

It involves referencing of information of a particular class in another class.

Question 20: What is the return type of the main () method?

It is void.

We hope that you have found our compilation of the best 20 java interview questions useful. Java Language is widely applicable because it is platform independent, therefore, can be used in nearly all the operating systems in the market today. We encourage you to share with us your opinion and thought on the above java interview questions.

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