JAVA is an important topic when it comes to some of the prestigious Interviews. Go through this complete article and learn some of the most important interview questions and their answers which are provided by Edureify. Edureify also provides courses on JAVA at an affordable price. Candidates will learn a lot from the systematic module that has been designed with the help of experts.
1) What is JAVA?
Answer: Java is a high-level programming language and is platform-independent. Java is a collection of objects. It was developed by Sun Microsystems. There are a lot of applications, websites, and games that are developed using Java.
2) What are the features of JAVA?
Answer: Features of Java are as follows:
- OOP concepts
- Object-oriented
- Inheritance
- Encapsulation
- Polymorphism
- Abstraction
- Platform independent: A single program works on different platforms without any modification.
- High Performance: JIT (Just In Time compiler) enables high performance in Java. JIT converts the bytecode into machine language and then JVM starts the execution.
- Multi-threaded: A flow of execution is known as a Thread. JVM creates a thread which is called the main thread. The user can create multiple threads by extending the thread class or by implementing the Runnable interface.
3) How does Java enable high performance?
Answer: Java uses the Just In Time compiler to enable high performance. It is used to convert the instructions into bytecodes.
4) Name the Java IDEs?
Answer: Eclipse and NetBeans are the IDEs of JAVA.
5) What do you mean by Constructor?
Answer: Constructor can be explained in detail with enlisted points: When a new object is created in a program a constructor gets invoked corresponding to the class.
The constructor is a method that has the same name as the class name.
If a user doesn’t create a constructor implicitly a default constructor will be created. The constructor can be overloaded. If the user created a constructor with a parameter then he should create another constructor explicitly without a parameter.
6) What is meant by the Local variable and the Instance variable?
Answer: Local variables are defined in the method and scope of the variables that exist inside the method itself. Instance variables are defined inside the class and outside the method and the scope of the variables exists throughout the class.
7) What is a Class?
Answer: All Java codes are defined in a Class. It has variables and methods. Variables are attributes that define the state of a class. Methods are the place where the exact business logic has to be done. It contains a set of statements (or) instructions to satisfy a particular requirement.
8) What is an Object?
Answer: An instance of a class is called an object. The object has a state and behavior. Whenever the JVM reads the “new()” keyword then it will create an instance of that class.
9)What are the OOPs concepts?
Answer: OOPs concepts include:
- Inheritance
- Encapsulation
- Polymorphism
- Abstraction
- Interface
10) What is Inheritance?
Answer: Inheritance means one class can extend to another class. So that the codes can be reused from one class to another class. The existing class is known as the Superclass whereas the derived class is known as a subclass.
11) What is Encapsulation?
Answer: Purpose of Encapsulation:
- Protects the code from others.
- Code maintainability.
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12) What is Polymorphism?
Answer: Polymorphism means many forms.A single object can refer to the superclass or subclass depending on the reference type which is called polymorphism.
- What is a Marker Interface?
Answer:- An empty interface in Java is referred to as a Marker interface. Serializable and Cloneable are some famous examples of Marker Interface.
- What is Object Cloning?
Answer:- An ability to recreate an object entirely similar to an existing object is known as Object Cloning in Java. Java provides a clone() method to clone a current object offering the same functionality as the original object. Also, check the official Website for more information on topics related to JAVA.
- Why is Java not completely object-oriented?
Answer:- Java is not considered a 100% object-oriented programming language because it still makes use of eight or more primitive data types like int, float double, etc.
- What is an object-oriented paradigm?
Answer:- A Paradigm that is based on the concepts of “Objects.” It contains data and code. Data that is in the form of fields, and regulation, that is in the form of procedures. The exciting feature of this paradigm is that the object’s procedures can access and often modify the data fields themselves.
- Define Wrapper Classes in Java.
Answer:- In Java, when you declare primitive data types, then Wrapper classes are responsible for converting them into objects(Reference types). Download the Eduriefy app to know more about the classes.
- Define Singleton Classes in Java.
Answer:- In Java, when you make the constructor of a class private, that particular class can generate only one object. This type of class is popularly known as a Singleton Class.
- Define package in Java.
Answer:- The package is a collective bundle of classes and interfaces and the necessary libraries and JAR files. The use of packages helps in code reusability.
- Can you implement pointers in a Java Program?
Java Virtual Machine takes care of memory management implicitly. Java’s primary motto was to keep programming simple. So, accessing memory directly through pointers is not a recommended action. Hence, pointers are eliminated in Java.
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- Differentiate between instance and local variables.
For instance, variables are declared inside a class, and the scope is limited to only a specific object.
A local variable can be anywhere inside a method or a specific block of code. Also, the scope is limited to the code segment where the variable is declared.
- Explain Java String Pool.
A collection of strings in Java’s Heap memory is referred to as Java String Pool. In case you try to create a new string object, JVM first checks for the presence of the object in the pool. If available, the same object reference is shared with the variable, else a new object is created.
- What is an Exception?
An Exception in Java is considered an unexpected event that can disrupt the program’s normal flow. These events can be fixed through the process of Exception Handling.
- What is the final keyword in Java?
The term final is a predefined word in Java that is used while declaring values to variables. When a value is declared using the final keyword, then the variable’s value remains constant throughout the program’s execution.
- What happens when the main() isn’t declared as static?
When the main method is not declared as static, then the program may be compiled correctly but ends up with a severe ambiguity and throws a run time error that reads “NoSuchMethodError.”
- What is JDK? Mention the variants of JDK?
Answer:- JDK is an abbreviation for Java Development Kit. It is a combined Package of JRE and Developer tools used for designing Java Applications and Applets. Oracle has the following variants.
- JDK Standard Edition
- JDK Enterprise Edition
- JDK Micro Edition
- What is the difference between JDK, JRE, and JVM?
Answer:- JVM has a Just in Time (JIT) compiler tool that converts all the Java source code into the low-level compatible machine language. Therefore, it runs faster than the regular application. JRE has class libraries and other JVM supporting files. But it doesn’t have any tool for java development such as a compiler or debugger.
JDK has tools that are required to write Java Programs and uses JRE to execute them. It has a compiler, Java application launcher, and an applet viewer.
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- What is a JIT compiler?
Answer:- JIT compiler refers to the Just in Time compiler. It is the simplest way of executing the computer code that takes in compilation during the execution of a program rather than before performance. It commonly uses bytecode translation to machine code. It is then executed directly.
- What are Brief Access Specifiers and Types of Access Specifiers?
Answer:- Access Specifiers are predefined keywords used to help JVM understand the scope of a variable, method, and class. We have four access specifiers.
- Public Access Specifier
- Private Access Specifier
- Protected Access Specifier
- Default Access Specifier
- How many types of constructors are used in Java?
There are two types of constructors that are used in Java.
- Parameterized Constructors: Parameterized constructor accepts the parameters with which users can initialize the instance variables. Users can initialize the class variables dynamically at the time of instantiating the class.
- Default constructors: This type doesn’t accept any parameters; rather, it instantiates the class variables with their default values. It is used mainly for object creation.
- Can a constructor return a value?
Answer:- Yes, A constructor can return a value. It replaces the class’s current instance implicitly; you cannot make a constructor return a value explicitly.
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- Explain ‘this’ keyword in Java.
Answer:- The term “this” is a particular keyword designated as a reference keyword. The “this” keyword is used to refer to the current class properties like method, instance, variable, and constructors.
- Explain the ‘super’ keyword in Java.
Answer:- The term “super” is a particular keyword designated as a reference keyword. The “super” keyword refers to the immediate parent class object.
- Explain Method Overloading in Java.
Answer:- The process of creating multiple method signatures using one method name is called Method Overloading in Java. Two ways to achieve method overloading are:
- Varying the number of arguments Changing the return type of the Method
- Can we overload a static method?
Answer:- No, Java does not support the Overloading of a static method. The process would throw an error reading “static method cannot be referenced.”
- Define Late Binding.
Answer:- Binding is a process of unifying the method call with the method’s code segment. Late binding happens when the method’s code segment is unknown until it is called during the runtime.
- Define Dynamic Method Dispatch.
Answer:- The Dynamic method dispatch is a process where the method call is executed during the runtime. A reference variable is used to call the super-class. This process is also known as Run-Time Polymorphism.
- Why is the delete function faster in the linked list than an array?
Answer:- Delete Function is faster in linked lists as the user needs to make a minor update to the pointer value so that the node can point to the next successor in the list
- Give a briefing on the life cycle of a thread.
The life cycle of a thread includes five stages, as mentioned below.
- New Born State
- Runnable State
- Running State
- Blocked State
- Dead State
- Explain the difference between >> and >>> operators.
Answer:- Although they look similar, there is a massive difference between both.
>> operator does the job of right shifting the sign bits
>>> operator is used in shifting out the zero-filled bits
- Brief the life cycle of an applet.
The life cycle of an applet involves the following.
- Initialization
- Start
- Stop
- Destroy
- Paint
- Why are generics used in Java Programming?
Answer:- Compile-time type safety is provided by using generics. Compile-time type safety allows users to catch unnecessary invalid types at compile time. Generic methods and classes help programmers specify a single method declaration, a set of related methods, or related types with an available class declaration.
- Explain the Externalizable interface.
Answer:- The Externalizable interface helps with control over the process of serialization. An “externalizable” interface incorporates readExternal and writeExternal methods.
- What is the Daemon Thread?
Answer:- The Daemon thread can be defined as a thread with the least priority. This Daemon thread is designed to run in the background during the Garbage Collection in Java. The setDaemon() method creates a Daemon thread in Java.
- Explain the term enumeration in Java.
Answer:- Enumeration or enum is an interface in Java. Enum allows sequential access to the elements stored in a collection in Java. Open the official website to know more.
- Why is Java Dynamic?
Answer:- Java is designed to adapt to an evolving environment. Java programs include a large amount of runtime information that is used to resolve access to objects in real-time.
- Can you run a code before executing the main method?
Answer:- Yes, we can execute any code, even before the main method. We will be using a static block of code when creating the objects at the class’s load time. Any statements within this static block of code will get executed at once while loading the class, even before creating objects in the main method.
- How many times is the finalize method called?
Answer:- The finalize method is called the Garbage collector. For every object, the Garbage Collector calls the finalize() method just one time.
- Can “this” and “super” keywords be used together?
Answer:- No, “this” and “super” keywords should be used in the first statement in the class constructor. The following code gives you a brief idea.
- What is a JSP page?
Answer:- JSP is an abbreviation for Java Servlet Page. The JSP page consists of two types of text.
- Static Data
- JSP elements
Frequently Asked Questions (FAQs)
Question:- What is Java used for?
Answer:- Java is used to write applications for different platforms that run JRE and supports applications that run on a single device like a desktop or mobile phone. Java can also be used to develop applications that work in a distributed manner.
Question:- What Does Java Mean?
Answer:- Java is an object-oriented programming language that produces software for multiple platforms. When a programmer writes a Java application, the compiled code (known as bytecode) runs on most operating systems (OS), including Windows, Linux and Mac OS
Question:- Is Java easy to learn?
Answer:- Java is easy to learn. Java was designed to be easy to use and is therefore easier to write, compile, debug, and learn than other programming languages. Java is object-oriented. This allows you to create modular programs and reusable code.
Question:- Which is easier: Python or Java?
Answer:- Java and Python are two of the most popular programming languages. Of the two, Java is the faster language, but Python is simpler and easier to learn.
