Java Developer Interview Questions

Java is an object-oriented programming language. It is the most extensively used programming language for Android development. It may also be used to develop desktop applications, web applications, and web services. As a consequence, we've developed a list of the most important Java Interview Questions you'll need to get your dream job in the IT industry.

1.What do you understand by marker interfaces in Java?

ANS:Marker interfaces, also known as tagging interfaces are those interfaces that have no methods and constants defined in them. They are there for helping the compiler and JVM to get run time-related information regarding the objects.

2.In Java, what is enumeration?

ANS:A list of named constants is referred to as an enumeration. Enumeration is a Java concept that defines a class type. Constructors, methods, and instance variables can all be found in an Enumeration. The enum keyword is used to build it. By default, each enumeration constant is public, static, and final. Even though enumeration has constructors and defines a class type, you don't use new to create an enum. Enumeration variables work similarly to primitive variables in terms of usage and declaration.

3.Define Inheritance?

ANS:Inheritance refers to the process by which one class gets the attributes (data members) and functionality (methods) of another class. The goal of inheritance is to allow code to be reused such that a class only has to develop unique features, while the rest of the common attributes and capabilities can be extended from another class. Classification of Children:A child class, subclass, or derived class is a class that extends the features of another class. Class for Parents:A parent class, super class, or base class is a class whose attributes and capabilities are used (inherited) by another class.

4.In Java, what is abstraction?

ANS:The basic blocks of Object-Oriented Programming are objects. A collection of properties and methods make up an object. We can use access modifiers to keep them hidden from the outside world. We can only provide the other applications access to the functions and properties they need. In OOPS, this is the overall technique for implementing abstraction.

5.In Java, what is encapsulation?

ANS:Encapsulation is a technique for hiding implementation details from users. When a data member is private, it can only be accessed by other members of the same class. No outside class has access to a class's private data member (variable). However, if we create public getter and setter methods to update (for example, void setName(String Name)) and read (for example, String getName()) the private data fields, the outside class can use those public methods to access those private data fields.

6.In Java, what is a collection?

ANS:Collections are similar to containers in that they hold several elements in one unit. A jar of chocolates, a list of names, and so on. Every programming language uses collections, and Java came with a few Collection classes - Vector, Stack, Hashtable, and Array.

7.In Java, what is an API?

ANS:The Java application programming interface (API) is a list of all Java development kit classes (JDK). All Java packages, classes, and interfaces, as well as their methods, fields, and constructors, are included. A programmer can get a lot of functionality out of these pre-written classes.

8.In Java, what is static?

ANS:A static member in Java is a member of a class that isn't associated with a class instance. Instead, the member is a member of the class. As a result, you don't need to create a class instance to access the static member.

9.In Java, what is a package?

ANS:In Java, a package is used to group together related classes. Consider it a folder in a file system. Packages help us avoid name clashes and write more maintainable code. Two types of packages are available: Packages that are already installed (packages from the Java API) Packages created by the user (create your own packages)

10.In Java, what is an abstract class?

ANS:An abstract class is one that is declared using the "abstract" keyword. It can have both abstract and concrete methods (methods without a body) (regular methods with body). Abstract methods aren't allowed in non-abstract classes.

11.How do I find out what Java version I have?

ANS:Use a command prompt/terminal to run java -version.

12.In Java, what is a class?

ANS:A class is a template that explains the data and behaviour associated with instances of that class. It is the basic building element of an object-oriented language like Java. When you instantiate a class, you're making an object that looks and behaves like other instances of that class. Variables contain data associated with a class or object, while methods implement the behaviour associated with a class or object.

13.What is the definition of core Java?

ANS:Sun's designation for Java SE, the standard edition, and a group of related technologies such as the Java Virtual Machine, CORBA, and so on is "Core Java." This is largely to distinguish itself from Java ME or Java EE, for example. It's also worth noting that they're referring to a library set rather than a programming language.

14.How can I get Java to work on Chrome?

ANS:Select the Security tab in the Java Control Panel. Choose an option. Java content must be enabled in the browser. To confirm the changes, click Apply and then OK. To activate the changes, restart the browser.

15.In Java, what is a string?

ANS:A string is a collection of characters; for example, "Hello" is a five-character string. Strings are immutable objects in Java, which means they can't be modified after they've been generated.

16.Why does Java not enable multiple inheritance?

ANS:Java only allows for multiple inheritance through interfaces. A class can implement as many interfaces as it wants, but it can only extend one other class. Multiple inheritance is not permitted due to the lethal diamond dilemma.

17.Why does Java not enable multiple inheritance?

ANS:Java only allows for multiple inheritance through interfaces. A class can implement as many interfaces as it wants, but it can only extend one other class. Multiple inheritance is not permitted due to the lethal diamond dilemma.

18.In Java, what is a singleton class?

ANS:The singleton design pattern is used to limit the number of times a class can be instantiated, ensuring that only one instance of the class exists in the JVM. To put it another way, a singleton class is one that can only contain one object (an instance of the class) per JVM instance.

19.Why is encapsulation required in Java?

ANS:In Java, encapsulation is a mechanism for combining code and data (variables) acting on data (methods) into a single unit. Encapsulation means that a class's variables are concealed from other classes and can only be accessed through its own methods.

20.In Java, how does a hashmap work?

ANS:In Java, HashMap is based on hashing techniques. It's a data structure that lets us store and retrieve objects in constant time O(1) if we know the key. Hash functions are used to link key and value in HashMap in hashing.

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