Java Interview Questions for fresher with Answers – Java is a popular programming language that is widely used for building web, desktop, and mobile applications. For freshers, Java interview questions typically focus on basic concepts such as object-oriented programming (OOP), syntax, and core features of the language. You might be asked about key principles like inheritance, polymorphism, encapsulation, and abstraction. Other common topics include understanding of data types, control structures (if-else, loops), exception handling, collections, and basic threading.

Being well-prepared for a Java interview means having a strong grasp of these foundational concepts, understanding how to write simple Java programs, and knowing how to solve problems using basic coding techniques. Interviewers might also test your understanding of how Java manages memory, garbage collection, and how the Java Virtual Machine (JVM) works.

Here the most important Java Interview Questions for fresher with Answers .

1.What is Java?

Java is a high-level, object-oriented programming language developed by Sun Microsystems. It is platform-independent due to its Write Once, Run Anywhere (WORA) capability. Java programs are compiled into bytecode which runs on the Java Virtual Machine (JVM). It supports features like automatic memory management (Garbage Collection), multithreading, and exception handling.

2.What is the JVM?

The Java Virtual Machine (JVM) is an abstract machine that enables a computer to run Java programs. It executes bytecode, which is a compiled form of Java code. JVM performs garbage collection and provides security features like sandboxing. The JVM is platform-dependent, but the bytecode it runs is platform-independent.

3.What is JDK?

The Java Development Kit (JDK) is a software development environment used for developing Java applications. It includes the JRE, an interpreter/loader (Java), a compiler (javac), an archiver (jar), and documentation generator (Javadoc). JDK is essential for compiling and running Java programs.

4.What is JRE?

The Java Runtime Environment (JRE) is a part of the JDK that allows users to run Java applications. It includes the JVM and essential libraries and components required to execute Java code. However, the JRE does not include development tools like the Java compiler.

5.What is a Class in Java?

A Class in Java is a blueprint for creating objects. It defines fields (attributes) and methods (functions) that an object will have. Classes are fundamental to object-oriented programming (OOP) in Java and support features like inheritance, polymorphism, and encapsulation.

6What is an Object in Java?

An Object is an instance of a class. It contains state (fields) and behavior (methods). Objects are created using the new keyword in Java. Objects interact with one another through method calls, and they are essential to implementing OOP principles in Java.

7.What is Inheritance in Java?

Inheritance allows one class (subclass) to inherit fields and methods from another class (superclass). It promotes code reuse and establishes a natural hierarchy between classes. Java supports single inheritance but allows multiple interfaces to be implemented.

8.What is Polymorphism in Java?

Polymorphism allows objects to be treated as instances of their parent class. In Java, there are two types: compile-time polymorphism (method overloading) and runtime polymorphism (method overriding). It enables flexibility in code and enhances extensibility.

9.What is Encapsulation in Java?

Encapsulation refers to the bundling of data (fields) and methods into a single unit (class) and restricting access to the data by making fields private. Access is provided through getter and setter methods, maintaining data security and integrity.

10.What is Abstraction in Java?

Abstraction in Java means hiding the implementation details and showing only the necessary functionality to the user. It is implemented through abstract classes and interfaces. Abstraction helps in reducing complexity and improving code maintainability.

11.What is an Interface in Java?

An Interface is a reference type in Java that contains only abstract methods and constants. Interfaces allow multiple inheritance and are used to define a contract that implementing classes must follow. From Java 8 onwards, interfaces can have default and static methods.

12.What is a Constructor in Java?

A Constructor is a special method in Java used to initialize objects. It is called when an instance of a class is created. Constructors have the same name as the class and do not have a return type. They can be overloaded to provide different ways to initialize objects.

13.What is Method Overloading in Java?

Method Overloading allows multiple methods in the same class to have the same name but with different parameter lists. It is a form of compile-time polymorphism. Overloading improves code readability and allows flexibility when calling methods with different arguments.

14.What is Method Overriding in Java?

Method Overriding occurs when a subclass provides a specific implementation of a method already defined in its superclass. It supports runtime polymorphism and ensures that the correct method is called based on the object’s runtime type.

15.What is a Static Keyword in Java?

The static keyword is used to declare members (variables, methods) that belong to the class rather than to any instance. Static methods can be called without creating an object of the class, and static variables are shared among all instances.

16.What is the Final Keyword in Java?

The final keyword can be applied to classes, methods, and variables. A final class cannot be inherited, a final method cannot be overridden, and a final variable cannot be reassigned. It helps to enforce immutability and protect code integrity.

17.What is a Package in Java?

A package is a namespace that groups related classes and interfaces together. It helps in organizing code and avoiding naming conflicts. The java.lang package is imported by default in all Java programs. Custom packages can also be created.

18.What is Exception Handling in Java?

Exception Handling in Java is a mechanism to handle runtime errors, ensuring the normal flow of the program. It uses try, catch, finally, throw, and throws keywords. Checked exceptions are handled at compile-time, and unchecked exceptions occur at runtime.

19.What is the Difference Between Checked and Unchecked Exceptions?

Checked exceptions are checked at compile-time, meaning the compiler ensures that they are either handled or declared using the throws keyword. Unchecked exceptions (subclasses of RuntimeException) occur at runtime and do not need to be explicitly handled.

20.What is Multithreading in Java?

Multithreading is the process of executing multiple threads simultaneously. Java supports multithreading via the Thread class and Runnable interface. Threads in Java share the same memory space, making it efficient for tasks like parallel execution.

21.What is Synchronization in Java?

Synchronization is a mechanism in Java that controls the access of multiple threads to shared resources. It prevents thread interference and ensures data consistency. The synchronized keyword can be used for methods or blocks to restrict access to only one thread at a time.

22.What is a String in Java?

A String in Java is an immutable sequence of characters. It is a class in the java.lang package. Once a string is created, it cannot be modified, but new strings can be created from it. String Pool is a feature that helps in optimizing memory for string literals.

23.What is StringBuffer in Java?

The StringBuffer class in Java represents a mutable sequence of characters. Unlike String, objects of StringBuffer can be modified without creating a new object. It is thread-safe and can be used when string modifications are required frequently.

24.What is StringBuilder in Java?

StringBuilder is similar to StringBuffer but is not synchronized, making it faster for single-threaded environments. Like StringBuffer, StringBuilder allows mutable string manipulation without creating new objects in memory.

25.What are Wrapper Classes in Java?

Wrapper classes in Java provide an object representation of primitive data types (e.g., Integer for int, Double for double). They are used when primitives need to be manipulated as objects, for example, in collections like ArrayList.

26.What is Autoboxing and Unboxing in Java?

Autoboxing is the automatic conversion of primitive types into their corresponding wrapper class objects. Unboxing is the reverse process, converting a wrapper class object back to a primitive type. This feature simplifies the use of primitive data types in contexts where objects are required, such as in collections.

27.What is an Array in Java?

An Array in Java is a data structure that holds a fixed number of elements of the same type. Arrays are indexed, with the first element at index 0. They can store both primitives and objects. Arrays have a fixed size, meaning their length cannot be changed once created.

 28.What is an ArrayList in Java?

An ArrayList is part of the Java Collections Framework and is a resizable array implementation of the List interface. Unlike arrays, ArrayLists can dynamically grow and shrink in size. It allows for random access of elements and supports null values.

29.What is the Difference Between Array and ArrayList in Java?

The main difference is that arrays are of fixed size, whereas ArrayLists are dynamic and can grow or shrink. Arrays can hold primitive types and objects, while ArrayLists only hold objects. ArrayList is part of the Java Collections Framework and offers methods like add(), remove(), and contains().

30.What is a HashMap in Java?

HashMap is a part of the Java Collections Framework and provides a way to store key-value pairs. It allows for fast access based on the key. HashMap is unsynchronized and allows one null key and multiple null values. It uses hashing to store entries in buckets for efficient access.

31.What is the Difference Between HashMap and Hashtable?

The main difference is that HashMap is unsynchronized, while Hashtable is synchronized, making it thread-safe. Hashtable doesn’t allow any null keys or values, while HashMap permits one null key and multiple null values. HashMap is faster in non-threaded applications.

32.What is a Set in Java?

A Set is a collection that contains no duplicate elements. The Set interface is part of the Java Collections Framework and includes implementations such as HashSet, TreeSet, and LinkedHashSet. Sets are useful when the uniqueness of elements is required.

33.What is a List in Java?

A List in Java is an ordered collection of elements. It can contain duplicate elements and allows random access to its elements. The List interface is part of the Java Collections Framework and includes implementations such as ArrayList, LinkedList, and Vector.

34.What is the Difference Between List and Set?

The key difference is that a List can contain duplicate elements, while a Set cannot. Lists maintain the insertion order, whereas Sets do not guarantee order unless using specific implementations like LinkedHashSet or TreeSet.

35.What is a Queue in Java?

A Queue is a collection that follows the FIFO (First In, First Out) principle. It is part of the Java Collections Framework and is used when elements need to be processed in order. Common implementations include LinkedList and PriorityQueue.

36.What is the Java Collections Framework?

The Java Collections Framework (JCF) provides a set of interfaces and classes for working with data structures like List, Set, Queue, and Map. It includes utility classes such as ArrayList, HashMap, HashSet, and methods for sorting, searching, and modifying data structures.

37.What is the difference between Comparable and Comparator?

Comparable is an interface used for natural ordering of objects by implementing the compareTo() method, whereas Comparator provides custom ordering by implementing the compare() method. Comparable affects the object’s class, while Comparator can be used externally to sort objects in different ways.

38.What is a Singleton Class in Java?

A Singleton class ensures that only one instance of the class is created and provides a global point of access to it. It is implemented by making the constructor private and providing a static method that returns the instance. Singletons are commonly used in logging and configuration management.

39.What is the Factory Design Pattern?

The Factory pattern is a creational design pattern that provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created. It is used when the exact type of object that will be created is not known until runtime.

40.What is Garbage Collection in Java?

Garbage Collection in Java is the process by which the JVM automatically identifies and reclaims memory that is no longer in use by objects. It helps in preventing memory leaks. Java’s garbage collector runs as a background thread and uses techniques like Mark-and-Sweep and Generational GC.

41.What is the Difference Between == and equals() in Java?

In Java, the == operator checks if two references point to the same object in memory, while the equals() method compares the actual content of two objects. For String and other object comparisons, equals() is typically overridden to compare values instead of memory addresses.

42.What is a Constructor Chaining in Java?

Constructor Chaining is the process of calling one constructor from another in the same or parent class. It allows code reuse and prevents duplication. Constructor chaining can be achieved using the this() keyword for the same class and super() for calling parent class constructors.

43.What is a Thread in Java?

A Thread is a lightweight process that can run concurrently with other threads. Java supports multithreading through the Thread class or Runnable interface. Threads share memory and resources, making it efficient for parallel execution.

44.What is Deadlock in Java?

A Deadlock occurs in Java when two or more threads are waiting for each other to release resources, causing them to block indefinitely. It can occur when threads have circular dependencies on locked resources. Synchronization and careful resource management help prevent deadlocks.

45.What is Volatile Keyword in Java?

The volatile keyword in Java is used to mark a variable so that its value is always read from and written to the main memory, ensuring visibility between threads. It prevents thread caching of variables, making volatile variables thread-safe for reading and writing.

 46.What is the Difference Between Process and Thread?

A process is an independent program with its own memory space, while a thread is a smaller execution unit within a process. Threads share the same memory space, allowing for efficient inter-thread communication, while processes are more isolated and require inter-process communication (IPC).

47.What is Exception Propagation in Java?

Exception Propagation refers to the process by which an exception is thrown from one method to another in the call stack. In Java, if an exception is not caught in a method, it propagates backward until it is caught or terminates the program. Checked exceptions must be handled using throws.

48.What is the use of the transient keyword in Java?

The transient keyword is used to prevent serialization of a particular field in a class. When an object is serialized, fields marked as transient are ignored, meaning they are not saved to the file. It is useful for handling non-serializable fields or security-sensitive data.

49.What is Reflection in Java?

Reflection is the ability in Java to inspect and modify the behavior of classes, methods, and fields at runtime. It is primarily used for dynamic class loading, method invocation, and retrieving metadata. Java provides the java.lang.reflect package for reflection.

50.What are Annotations in Java?

Annotations provide metadata about the program and do not affect program execution directly. Annotations can be used to provide information to the compiler, generate code, or configure runtime behavior. Common annotations include @Override, @Deprecated, and custom annotations.