Top 25+ Top Java Developer Interview Questions and Answers [2024]

I have prepared a list of 25+ most frequently asked Java developer interview questions & answers that will help you crack this interview and land your dream job. The interview questions are specially picked by industry experts, and answers are prepared in a tricky and impressive manner. 

Keep reading this blog post to level up your understanding & secure your chances to grab the attention of hiring managers. Boost your confidence with these below-mentioned Java developer interview questions and answers.

Shall we begin?

Q1. What are the top features of Java Programming Language?

Java is an object-oriented, multi-platform & network-centric programming language applied as a platform itself. 

Java has some top features that make it a most common programming language, and some of them include:

• It works as an object-oriented programming itself.
• It is a very simple programming language & easy to write.
• It has platform independence that allows Java codes to run on any JVM-installed platform.
• Java has the feature of multithreading, which allows various threads to run smoothly.
• Java has an in-build security feature that protects from malware attacks.
• Itr has an automated memory management feature & helps in managing automated memory allocation & deallocation.

Q2. What do you mean by JVM?

A major component of Java, JVM, refers to the Java Virtual Machine. It helps in the execution of Java bytecode that represents Java programs. JVM helps to load, implement & execute the bytecode developed in Java.

JVM, being an abstract machine helps Java to become platform-independent. Apart from this, JVM also helps in managing resources, garbage collection & memory management. 

Q3. What type of memory allocations are available in Java?

Java has five major types of memory allocations, and those are;

• Heap memory.
• Stack memory.
• Class memory.
• Native Method Stack memory.
• Program Counter-memory.

Q4. Explain the concept of the JIT compiler.

JIT compiler refers to the Just In Time compiler, which is used widely to boost the overall performance of Java. It is one of the popular central features of JVM. This JVM mechanism helps to optimize code during runtime. 

Apart from code optimization, JIT can also perform tasks such as lock eliding, lock coarsening, escape analysis & code inlining. The compilation occurs during the runtime, speeding up the Java program execution. 

JIT helps in boosting overall performance by converting often-used codes into native codes and helping them to run faster.

Q5. What do you mean by Object cloning?

Object cloning in Java refers to the method of developing an exact copy of a specific object. It is the method of creating an object with the same state as the original object. In order to get this, Java offers a command called “clone()” to use this special functionality. 

The object clone is a secured method; hence, you have to override it first. Java offers two different types of object cloning, and they include Shallow cloning & deep cloning. 

Deep cloning helps in flexible object management, while shallow cloning helps to copy the immediate values of an object.

Q6. What do you mean by a ClassLoader?

A ClassLoader in Java refers to the subsystem of JVM, which is responsible for loading class files at the time of program execution. 

There are three different types of ClassLoader, and they are extension classloader, system/application classloader & bootstrap classloader. 

The system/application classloader helps to load the class files from the classpath, while the extension classloader helps to load the jar files which are located in the Java home directory.

Q7. State the difference between the process & the program.

The program refers to the non-active entity of the application that consists of a huge collection of codes essential to execute a particular operation. A program is an essential static entity and does not execute anything by itself. 

On the other hand, the process refers to the program that is already executed. This dynamic entity incorporates the program code, the latest resources, and activities at the time of execution. 

Q8. Can you explain object-oriented programming?

Object-oriented programming or OOP refers to the programming entity that is dependent on the idea of objects. Programs are highly organized around the objects in Object-oriented programming. The objects must have several properties, such as attributes & behaviors. 

Object-oriented programming focuses on polymorphism, encapsulation, abstraction &inheritance. 

Q9. What are some primary features of an interface?

Some primary features of an interface include static methods, no constructors, constants, default methods, multiple inheritance & abstract methods. 

Q10. What do you mean by packages in Java & state its advantages?

Packages in Jave refer to the collection of related interfaces & classes that are combined together. Developers can start code optimization seven modularization by using these packages in Java.

Some advantages of packages in Java are;

• The package offers easy access control.
• The package gets rid of name clashes.
• The packages in Java boost manageability by grouping related code together, allowing debugging & updates.
• It helps in namespace management for interfaces and classes.

Q11. What are the different data types in Java?

Java has two different data types they are Primitive Data Types & Object Data Types or Non-Primitive Data Types.

Primitive data types refer to single values that have no special capabilities. There are eight different types of primitive data types and they include byte, long, short, boolean, float, char, int, and double.

Non-primitive data types refer to the data types that consist of a memory address of the variables as they can’t directly store them in the memory. There are five types of non-primitive data types & array, object, strings, class & interface.

Q12. How many different memory storage are available in JVM?

Java Virtual Machine has five different types of memory storage, and they include Class area, stack, native method stack, program counter register & heap.

Class area memory storage stores every class’s class-level data. Stack stores partial results and data that are required when performing linking and returning value for a specific method. 

Native method stack helps in storing the native processes of an application, while program counter register memory storage helps to store the Java Virtual Machine’s address, which has already been executed. 

Heap helps to create objects or helps to store objects while allocating memory to objects at the time of run time.

Q13. State the difference between the local variable & instance variable.

Instance variables refer to the variables that are resided outside the method and inside the class and their scope of variables exists over the class. On the other hand, Local variables refer to the variables of which scope exists only inside the method.

Local variables are there only at the time of method execution, whereas instance variables are there as long as the object is there. 

Local variables do not have a default volume, while instance variables have a default value. 

Q14. What do you mean by String Java Pool?

String Java Pool is a very well-known feature of Java and is widely used by developers and programmers. String Java pool refers to the storage area in Java’s Heap memory, and it helps in storing the String literals. Through sharing, String Java Pool helps to reduce the temporary String Object. 

While creating a string literal, Java always starts by checking the String Java Pool first.

Q15. What do you mean by Wrapper class in Java?

Wrapper Class in Java refers to the object class that sums up the primitive data types. Primitive data types help you create new data types.

There are eight major types of Wrapper classes in Java, and they include Short, Long, Byte, Boolean, Integer, Float, Double, & Character. As a developer, you can also create Custom Wrapper classes in Java, which is quite similar to the C programming language structure. 

The key reasons for using a Wrapper Class in Java are;

• It offers methods such as present () & value().
• Wrapper classes in Java are immutable & final ones.
• It offers you the exclusive unboxing & autoboxing feature. 

Q16. Explain the concept of static variables.

Static variables are referred to as those when both the instances or objects of a class share similar variables. Static variables are defined by static keywords. 

Static variables can be stored within the class area and as a developer, we aren’t required to create objects for accessing these variables.

These types of variables help your program to become highly memory efficient as it saves memory. 

Q17. State the difference between Systems.in, System.err & System.out.

Java has some standard streams, and they are systems.in, System.err & System.out., System.in refers to the system that has a standard input system and helps in reading the inputs from the keyboard, whereas System.out refers to Java’s standard output stream and helps to print output into the console. 

System.err refers to Java’s standard error stream which helps to output error messages. 

Q18. What do you mean by FileOutputStream & FileInputStream?

FileInputStream in Java refers to the stream that helps to read data from a file as a stream of bytes. It is frequently used for binary data reading like audio files or images. 

On the other hand, FileOutPutStream in Java refers to the stream that helps to write raw data byte-by-byte into the offered file descriptor. It is frequently used for raw byte data such as pictures. 

Q19. How many types of operators are there in Java?

In Java, operators are referred to as the specific types of symbols applied to perform some major operations over values & variables.

The ten key types of operators in Java are;

• Unary operators
• Bitwise operators
• Arithmetic operators
• Relational operators
• Ternary operators
• Shift operators
• Assignment operators
• Instance of operators
• Postfix operators
• Logical operators

Each type of operator offers specific operations on values & variables, encouraging different tasks of programming.

Q20. What are the major purpose of BufferedOutputStream & BufferInputStream classes?

The major purpose of the classes BufferInPutStream & BufferInPutStream is to boost the effectiveness of output & input operations. BufferInPutStream helps to read data to a buffer prior to processing them, boosting the speed of data access and decreasing the number of disk reads.

On the other hand, BufferOutPutStream helps to write data before it is written to the file, boosting the over-performance and decreasing the number of disk writes.

Both of these classes help in handling large numbers of data smoothly. 

Q21. What do you mean by FilterStreams?

FilterStreams refers to the feature Java that is widely used in data filtering as it is written to or read from a stream. FilterStreams are sub-categories of FilterInPutStream & FilterOutPutStream.

As a developer, you will be able to change and edit data flow without losing the original stream classes. 

Q22. What do you mean by array in Java?

An array in Java refers to a set of elements of a similar type stored in a nearby memory location. These are frequently used to collect several values of a single variable, making it easily accessible to handle huge amounts of data. 

Arrays in Java can be accessed using an index starting from 0. Arrays offer the easiest ways to manipulate and organize valuable data.

Q23. What are the different types of arrays?

Two different types of arrays are Single-dimensional arrays and Multi-dimensional arrays. 

Single dimensional arrays have only one dimension which means an array of strings.

Multi-dimensional arrays have two or more dimensions like three-dimensional or two-dimensional arrays.

Single-dimensional arrays are lists of elements, such as lists of numbers, whereas multidimensional arrays are grid-like formats, such as matrices or tables.

Q24. What are some major advantages & disadvantages of an array?

Advantages of Arrays include:

• Arrays help to store data effectively in memory. 
• Arrays offer quick data retrieval due to the storage of data in contiguous memory areas.
• Due to easy accessibility, arrays are the best choice for newcomers who want to learn programming.

Disadvantages of Arrays include:

• Arrays are rigid due to their limited support and data types; hence, linked lists and trees are the best options.
• The fixed size of arrays also served as a disadvantage.
• Arrays have failed to support complex data types such as structures and objects.

Q25. What is the major purpose of a default constructor?

Default constructor refers to the type of constructor that usually does not accept the parameters of any value. The major purpose of it is to set initial values for objects’ attributes. 

The default constructor has no arguments and is created by default when no other constructors are defined by the user. The other purpose of the default constructor is object creation. 

Q26. What are various ways to create objects in Java?

To create objects in Java, there are different ways available. The most frequently used way is to use the “new” keyword, such as “MyClass obj=new MyClass(). Another major way is to use ‘Class.forName()’ which is able to load a class dynamically.

To create a copy of a preexisting object, you should use “clone().” 

Apart from these, you can also use object deserialization & serialization to create an object.

Q27. What do you mean by marker interface?

A marker interface refers to the interface identified as an empty interface. Serializable, Remote interfaces, & Cloneable are some common marker interfaces. 

Marker interfaces help the JVM and compiler to run time-related data related to the objects. Marker interface is generally used to identify that a class has some particular behavior or property. These can offer metadata about the class to the runtime of Java. 

Q28. What do you mean by an interface?

An interface in Java refers to the functionality to get abstraction. This highlights the behavior of the class by offering an abstract type. 

An interface must have variables and methods, but they should be abstract. 

Q29. How do you differentiate between interface and abstract class?

There are huge ways to differentiate between abstract class and interface. Abstract class supports multiple inheritance while interface offers support to multiple implementations. The abstract class consists of data members & constructors, while the interface does not consist of data members and constructors. 

Both the complete and incomplete members are carried by the abstract class, while the interface only carries incomplete members. Due to the presence of complete members, an abstract class can be static, whereas an interface can not be static due to the presence of incomplete members.