100+ Java Interview Questions For Freshers

100+ Java Interview Questions For Freshers

Java interview questions are a critical component of technical job interviews for roles ranging from software developers to system architects. Understanding the wide range of questions that can be asked during these interviews helps candidates demonstrate their knowledge, problem-solving abilities, and practical skills in one of the world’s most popular programming languages.

Importance of Java Interview Questions

1. Assessing Core Knowledge: Java is an object-oriented, class-based language with strong ties to fundamental programming concepts like inheritance, polymorphism, encapsulation, and abstraction. Java interview questions help assess how well a candidate understands these principles and whether they can apply them effectively in real-world scenarios. Companies use these questions to measure a candidate’s grasp of basic syntax, data structures, and algorithms, all of which are vital for software development roles.
2. Evaluating Problem-Solving Skills: Beyond theoretical knowledge, Java interview questions often focus on problem-solving abilities. They may include coding challenges, algorithm design, and questions around optimizing code. This gives interviewers insight into how candidates approach complex problems, write efficient code, and use Java’s extensive libraries and frameworks to their advantage.
3. Demonstrating Practical Experience: Many Java questions revolve around memory management, multithreading, or using Java Collections Framework, which are essential for developing robust, scalable applications. These questions allow candidates to showcase their experience with building applications, handling concurrency, and managing resources efficiently.
4. Testing Advanced Concepts: For more senior positions, Java interviews often include questions on JVM internals, garbage collection, and design patterns. Mastery of these advanced topics indicates a deep understanding of Java and how to optimize it in performance-critical environments.

List of Java Interview Questions :

1. What is a class in Java?

Java encapsulates the codes in various classes that define new data types, which are used to create objects. These objects are the building blocks of Java programs.

2. What is a JVM (Java Virtual Machine)?

JVM is the runtime environment for compiled Java class files. It allows Java code to run on different platforms without modification.

3. What is the right data type to represent a price in Java?

For representing prices in Java, the BigDecimal type is recommended when memory is not a concern, and precision is critical. Alternatively, you can use double with predefined precision.

4. Does Java support multiple inheritances?

No, Java does not support multiple inheritances. It uses interfaces to achieve a form of multiple inheritance by allowing a class to implement multiple interfaces.

5. What are the supported platforms by Java Programming Language?

Java is platform-independent and runs on various platforms, including Windows, Mac OS, and different versions of UNIX/Linux, such as HP-Unix, Sun Solaris, Red Hat Linux, and more.

6. List any five features of Java.

Java boasts several essential features, including being Object-Oriented, Platform-Independent, Robust, Interpreted, and Multi-threaded.

7. Explain method overloading.

Method overloading occurs when a Java program contains multiple methods with the same name but different parameters. It allows for the creation of multiple methods with the same name for various use cases.

8. What restrictions are placed on the location of a package statement within a source code file?

A package statement must appear as the first line in a source code file, eliminating blank lines and comments.

9. What method is used to specify a container’s layout?

The setLayout() method is used to specify a container’s layout in Java, allowing you to define how components are arranged.

10. What is the immediate superclass of the Applet class?

The immediate superclass of the Applet class is the Panel class in Java.

11. What are the access modifiers in Java?

Java provides three primary access modifiers: public, protected, and private, with the default modifier (also known as package-private) being used when no identifier is specified explicitly. These modifiers control the visibility and accessibility of classes, methods, and variables.

12. What are packages?

A package in Java is a collection of related classes and interfaces that provide access protection and namespace management. Packages help organize and structure code in larger applications.

13. What is meant by Inheritance, and what are its advantages?

Inheritance is the process of inheriting all the features from a class, allowing a subclass to access the variables and methods of the superclass. The advantages of inheritance include code reusability and improved accessibility of superclass members by subclasses.

14. Can we rethrow the same exception from a catch handler?

Yes, you can rethrow the same exception from a catch handler in Java. If you want to rethrow a checked exception from a catch block, you need to declare that exception.

15. What value is a variable of the String type automatically initialized?

The default value of a String type is null in Java.

16. When a thread blocks on I/O, what state does it enter?

When a thread blocks on I/O, it enters the “waiting” state.

17. Which containers use a Flow Layout as their default layout?

The Panel and Applet classes use the Flow Layout as their default layout.

18. Explain Java Coding Standards for Constants?

In Java, constants are created using the static and final keywords. Constants typically contain only uppercase letters, and if the constant name is a combination of two words, it should be separated by an underscore. It’s recommended to use short, meaningful names for constants.

19. What is synchronization, and why is it important?

Synchronization in Java refers to controlling the access of multiple threads to shared resources. It is crucial because, without synchronization, multiple threads might access or modify shared objects concurrently, leading to critical errors and data corruption.

20. Explain Java Coding Standards for variables?

In Java, variable names should start with lowercase letters, be nouns, and use short, meaningful names. If variable names consist of multiple words, each inner word should start with an uppercase letter.

21. What is an abstract class?

An abstract class in Java is designed with implementation gaps for subclasses to fill in. It is deliberately incomplete and cannot be instantiated.

22. Name three Component subclasses that support painting?

The Canvas, Frame, Panel, and Applet classes in Java support painting.

23. What is the difference between JDK and JVM?

JDK (Java Development Kit) is used for development purposes and provides all the tools and executables needed to compile, debug, and execute Java programs. JVM (Java Virtual Machine) is the runtime environment that allows Java programs to run on different platforms.

24. Why doesn’t Java support multiple inheritances?

Java doesn’t support multiple inheritances due to the “Diamond Problem,” a situation that arises when a class inherits from two classes that have a common superclass. To avoid ambiguity and potential issues, Java uses interfaces to provide a form of multiple inheritance.

25. What modifiers may be used with an inner class that is a member of an outer class?

An inner class can be declared with access modifiers such as public, protected, private, static, final, or abstract.

26. Which java.util classes and interfaces support event handling?

Event handling in Java is supported by the EventObject class and the EventListener interface, which allow for the processing of events in applications.

27. What is a transient variable?

A transient variable in Java is a variable that may not be serialized. When an object is serialized, transient variables are not included in the serialized output.

28. Is null a keyword?

No, “null” is not a keyword in Java. It represents a special value that indicates the absence of a reference to an object.

29. What is an applet?

An applet is a dynamic and interactive program that runs inside a web page when accessed through a Java-capable web browser.

30. What is the lifecycle of an applet?

The lifecycle of an applet involves several methods:

• init(): Called when the applet is first loaded.
• start(): Called each time the applet is started.
• paint(): Called when the applet is minimized, maximized, or needs to be redrawn.
• stop(): Used when the browser moves off the applet’s page.
• destroy(): Called when the browser is finished with the applet.

31. What’s new with the stop(), suspend(), and resume() methods in JDK 1.2?

In JDK 1.2, the stop(), suspend(), and resume() methods have been deprecated, as they had limited use and were replaced with more advanced threading techniques.

32. What is the Vector class?

The Vector class in Java provides a dynamic and growable array of objects. It allows for the storage of a variable number of elements and automatically resizes itself as needed.

33. What is the difference between the >> and >>> operators?

The >> operator shifts bits to the right, preserving the sign bit (arithmetic right shift), while the >>> operator also shifts bits to the right but zero-fills the bits that have been shifted out (logical right shift).

34. What is the difference between this() and super()?

this() is used to invoke a constructor of the same class, while super() is used to invoke a constructor of the superclass.

35. What is a native method?

A native method in Java is a method that is implemented in a language other than Java, typically in C or C++. Native methods are used for tasks that require low-level system interaction.

36. What value does readLine() return when it has reached the end of a file?

The readLine() method returns null when it has reached the end of a file, indicating there are no more lines to read.

37. What is the Java API?

The Java API (Application Programming Interface) is a vast collection of ready-made software components that provide a wide range of functionalities, such as GUI (Graphical User Interface) widgets and data manipulation tools.

38. Why are there no global variables in Java?

Java does not support global variables to maintain code integrity and prevent issues like namespace collisions. Encapsulation and access control are promoted through the use of classes and object-oriented programming principles.

39. What are different types of access modifiers?

Java provides four primary access modifiers: public, private, protected, and the default (package-private). These modifiers control the visibility and accessibility of classes, methods, and variables.

40. What is a constructor?

A constructor is a special method used to initialize objects in Java. Constructors have the same name as the class and do not return any value. They are called when an object of the class is created and are responsible for setting initial values.

41. What is an Iterator?

An Iterator in Java is an interface used to step through the elements of a Collection. It allows for the processing of each element in a Collection and is implemented differently for each Collection type.

42. What is the difference between Reader/Writer and InputStream/OutputStream?

Reader/Writer classes in Java are character-oriented, while InputStream/OutputStream classes are byte-oriented. Reader/Writer classes are used for reading and writing character data, whereas InputStream/OutputStream classes are used for reading and writing byte data.

43. What is servlet?

A servlet is a module that extends request/response-oriented servers, such as Java-enabled web servers. It handles HTTP requests, processes them, and returns dynamic content to the web client.

44. What is clipping?

Clipping in Java is the process of confining paint operations to a limited area or shape. It restricts the drawing or rendering of objects to a specified region.

45. What is a memory leak?

A memory leak occurs when an application allocates memory for objects but fails to release or deallocate that memory properly. This leads to a gradual increase in memory consumption and can result in performance issues and system instability.

46. Can a for statement loop indefinitely?

Yes, a for statement can loop indefinitely if it is not controlled by a terminating condition. For example, for(;;) creates an infinite loop.

47. Explain Java Coding Standards for Methods?

• Method names should start with lowercase letters.
• Method names are typically verbs.
• Short, meaningful names are recommended.
• If a method name consists of multiple words, each inner word should start with an uppercase letter.

48. Why is Java not a pure Object-Oriented language?

Java is not considered a pure Object-Oriented language because it supports primitive types, such as int, byte, short, and long, which are not objects. In pure Object-Oriented languages, everything is treated as an object.

49. What are the access modifiers?

Access modifiers in Java are keywords that control the visibility and accessibility of classes, methods, and variables. The primary access modifiers are public, private, protected, and the default (package-private) modifier.

50. Can we overload the main method?

Yes, the main() method in Java can be overloaded. You can have multiple main() methods with different parameter lists, but the entry point for execution remains the standard public static void main(String[] args).

51. What is a method in java?

A method in Java is a block of code that contains the executable logic for a specific task. It typically consists of a method name, parameters, a return type, and a body of executable code.

52. Explain automatic type conversion in Java?

Automatic type conversion in Java allows the implicit conversion of one data type to another under specific conditions. For example, when assigning an int to a float, the int is automatically converted to a float because the destination type is larger and can accommodate the source type.

53. What is the difference between the prefix and postfix forms of the ++ operator?

The prefix form of the ++ operator (++i) increments the value of the variable before its current value is used in an expression. The postfix form (i++) uses the current value of the variable in an expression and then increments it.

54. In how many ways can we do exception handling in Java?

Exception handling in Java can be done in two ways:

1. By specifying a try-catch block to catch exceptions.
2. By declaring a method with a throws clause to propagate exceptions.

55. What does null mean in Java?

In Java, null is a special value that indicates the absence of an object reference. It is used when a variable does not point to any valid object.

56. Can we define a package statement after the import statement in Java?

No, a package statement must appear as the first line in a source code file, before any import statements or other code. It cannot be placed after import statements.

57. How many objects are created in the given piece of code?

In the provided code, only two objects are created: c1 and c3. c2 is declared but not initialized, so it does not create an object.

58. What is JSP?

JSP (JavaServer Pages) is a technology used for creating dynamic and interactive web applications. It allows embedding Java code within HTML pages to generate dynamic content.

59. What is the purpose of Apache Tomcat?

Apache Tomcat is a web server and servlet container that is used to run Java web applications. It provides a runtime environment for executing servlets and JavaServer Pages (JSP).

60. How are objects stored in memory in Java?

Objects in Java are stored in memory on the heap. When an object is created, memory is allocated for it on the heap, and the object’s reference is stored on the stack or within other objects.

61. Can we catch more than one exception in a single catch block?

Yes, in Java, it is possible to catch multiple exceptions in a single catch block by using a vertical bar (|) to separate the exception types.

62. What is the importance of the finally block in Java?

The finally block in Java is used for cleaning up resources and executing code that should always be run, regardless of whether an exception is thrown or not. It ensures that resources are released properly.

63. What is UNICODE?

UNICODE is a standardized character encoding that represents most of the world’s written languages. It uses 16 bits to represent each character, allowing for a wide range of characters and symbols to be encoded.

64. Explain the main() method in Java?

The main() method in Java is the entry point of a Java application. It is a standard method that takes an array of strings as its argument (String[] args) and is responsible for launching the program’s execution.

65. How are destructors defined in Java?

In Java, there are no destructors defined explicitly. Java uses automatic garbage collection to reclaim memory, and developers do not need to explicitly release resources. This is in contrast to languages like C++ where destructors are used to release resources.

66. What will be the output of Round(3.7) and Ceil(3.7)?

The Round(3.7) function returns 4, and the Ceil(3.7) function also returns 4.

67. What is a synchronized method?

A synchronized method in Java is a method that is used to control access to an object or a block of code. It ensures that only one thread can execute the synchronized method at a time, preventing concurrent access.

68. Can you cast any other type to a Boolean type with type casting?

No, you cannot cast other data types to a Boolean type using type casting. Casting between incompatible data types is not allowed in Java.

69. What are synchronized methods and synchronized statements?

Synchronized methods are Java methods that are explicitly marked as synchronized using the synchronized keyword. They ensure that only one thread can execute the method at a time. Synchronized statements are used to create synchronized blocks of code, providing finer-grained synchronization control.

70. What is the difference between access specifiers and access modifiers in Java?

In Java, access specifiers (e.g., public, private, protected, and default) control the visibility and accessibility of class members, while access modifiers (e.g., static, final, abstract) modify the behavior of class members.

71. Explain creating threads by implementing the Runnable interface.

To create threads by implementing the Runnable interface, you define a class that implements the Runnable interface and provides an implementation for the run() method. You then create instances of your Runnable class and pass them to Thread objects. The run() method defines the code that will run in a separate thread when the start() method of the Thread object is called.

72. When do we use synchronized methods in Java?

Synchronized methods are used when multiple threads need to access a method that can manipulate the internal state of an object. By marking a method as synchronized, you ensure that only one thread can execute the method at a time, preventing concurrent modifications to the object’s state.

73. Can you call one constructor from another if a class has multiple constructors?

Yes, in Java, you can call one constructor from another within the same class using the this() keyword. This is known as constructor chaining and is often used when a class has multiple constructors with varying parameters to avoid code duplication.

74. What is type casting?

Type casting is the process of converting a value from one data type to another in a programming language. In Java, type casting can be explicit (using casting operators) or implicit (automatic conversion when safe).

75. What is the difference between inner class and nested class?

In Java, an inner class is a non-static class defined within another class. A nested class is a broader term that includes both inner classes and static nested classes. Inner classes have access to the instance variables of the enclosing class, while static nested classes do not.

76. Where and how can you use a private constructor?

A private constructor can be used to prevent the instantiation of a class from outside that class. It is often used in utility classes that provide only static methods and do not need to be instantiated.

77. What is the Vector class?

The Vector class in Java is a dynamic array-like data structure that can hold multiple elements. It automatically resizes itself when the number of elements exceeds its capacity.

78. Why do we need wrapper classes?

Wrapper classes in Java are used to convert primitive data types into objects. They are useful when you need to work with objects instead of primitives, such as when dealing with collections or generics that require objects.

79. Does Java allow Default Arguments?

No, Java does not support default arguments in methods. All arguments must be explicitly provided when calling a method.

80. Which number is denoted by a leading zero in Java?

In Java, a leading zero denotes an octal (base-8) number. For example, 012 represents the decimal number 10.

81. What is a set in Java?

A set in Java is a collection that does not allow duplicate elements. It is often used to represent a mathematical set and provides methods for set operations such as union, intersection, and difference.

82. What is a Map in Java?

A map in Java is a collection that stores key-value pairs. It allows you to associate values (the “values”) with unique keys, and it provides methods to retrieve and manipulate those values based on their keys.

83. What is polymorphism in Java?

Polymorphism in Java is a concept that allows objects of different classes to be treated as objects of a common superclass. It facilitates the development of more flexible and reusable code by enabling a single interface to represent different types of objects.

84. What are checked and unchecked exceptions in Java?

Checked exceptions are exceptions that must be declared or caught using try-catch blocks. Unchecked exceptions, also known as runtime exceptions, do not require explicit handling. They are subclasses of RuntimeException.

85. What is the purpose of the static keyword in Java?

The static keyword is used in Java to create class-level variables and methods that are shared among all instances of a class. It allows access to the methods or variables without creating an instance of the class.

86. What is the super keyword used for in Java?

The super keyword is used to refer to the superclass (parent class) of a derived class (child class). It can be used to access superclass methods, constructors, or variables.

87. What is a ternary operator in Java?

The ternary operator, also known as the conditional operator, is a shorthand way to write simple if-else statements. It has the form condition ? expression1 : expression2. If the condition is true, it evaluates to expression1; otherwise, it evaluates to expression2.

88. Explain the difference between ArrayList and LinkedList in Java.

ArrayList and LinkedList are both implementations of the List interface in Java. The primary difference is in their underlying data structures. ArrayList uses an array to store elements, while LinkedList uses a doubly-linked list. ArrayList is more efficient when it comes to random access, while LinkedList is more efficient for insertions and deletions.

89. What are annotations in Java?

Annotations in Java are a form of metadata that can be added to Java code elements such as classes, methods, and fields. They provide information about the code to the compiler and can be used for various purposes, including documentation, code analysis, and code generation.

90. What is the purpose of the finally block in exception handling?

The finally block is used in exception handling to ensure that a particular block of code executes, whether or not an exception is thrown. It is often used for resource cleanup, ensuring that resources are released even in the presence of exceptions.

91. What is the purpose of the throws clause in method declarations?

The throws clause in method declarations is used to indicate that a method may throw certain types of exceptions. It is a way of declaring the exception types that the method might not handle and passes the responsibility to the calling code to handle those exceptions.

92. What is the purpose of the throw statement in Java?

The throw statement is used in Java to manually throw an exception. It is typically used to indicate an error or exceptional condition within the code, and it can be followed by an exception object that describes the error.

93. What is a Java package and how is it used?

A Java package is a way of organizing and categorizing related classes and interfaces. Packages help prevent naming conflicts and provide a namespace for classes. They are declared using the package keyword, and classes can be grouped within packages by specifying the package name at the beginning of the source file.

94. What is the purpose of the import statement in Java?

The import statement in Java is used to make classes and packages from other packages available to your code. It simplifies class referencing by allowing you to use short names, such as import java.util.ArrayList to access the ArrayList class without using the fully qualified name.

95. What are the key principles of Object-Oriented Programming (OOP)?

The key principles of Object-Oriented Programming (OOP) include encapsulation, inheritance, and polymorphism. OOP is based on the concept of objects, which represent real-world entities and their interactions.

96. What is encapsulation in Java?

Encapsulation is one of the core principles of OOP and refers to the practice of bundling data (attributes) and the methods (functions) that operate on the data into a single unit, called a class. It helps in data hiding, protecting data from unauthorized access.

97. What is inheritance in Java?

Inheritance is a fundamental concept in OOP that allows a class to inherit the properties and behaviors (methods and fields) of another class. It promotes code reuse and the creation of a hierarchical structure of classes.

98. What is polymorphism in Java?

Polymorphism is another key concept in OOP, allowing objects to be treated as instances of their parent class or interfaces. It enables flexibility and the use of a common interface to work with objects of different types.

99. How does Java support multiple inheritance?

Java supports multiple inheritance through interfaces. A class can implement multiple interfaces, inheriting their method signatures without the issues associated with multiple inheritance seen in some other programming languages.

100. What is method overloading in Java?

Method overloading in Java occurs when multiple methods in the same class have the same name but different parameters. It allows developers to create multiple methods with the same name, making code more readable and expressive.

About Java :

Java is a versatile, object-oriented programming language designed by Sun Microsystems in 1995. It is widely used for building applications ranging from desktop software to large-scale enterprise systems. Java’s platform independence—enabled by its “write once, run anywhere” (WORA) principle—makes it one of the most popular languages globally.

At the core of Java’s platform independence is the Java Virtual Machine (JVM), which allows Java programs to run on any device or operating system that has a JVM installed. Java code is compiled into bytecode, which the JVM interprets and runs, ensuring compatibility across platforms.

Java supports object-oriented programming (OOP) principles like encapsulation, inheritance, abstraction, and polymorphism, making it a powerful tool for building modular and reusable code. These OOP principles also promote clean architecture and maintainable software development.

The language offers a robust library of APIs and frameworks that simplify the development process. The Java Collections Framework, for example, provides efficient data structures like lists, sets, and maps, making Java particularly useful for handling large datasets. Additionally, Java’s robust concurrency model supports multithreading, making it ideal for performance-critical applications.

Java is also a dominant language in enterprise-level solutions, with frameworks like Spring and Hibernate simplifying development for large, complex applications. Its use in Android development has further increased its popularity, as Java is the primary language for building Android apps.

Security is another strong suit, with built-in mechanisms like bytecode verification and a sophisticated exception handling system that ensures error management and safer code execution.

With its large ecosystem, active community support, and continued evolution, Java remains a top choice for developers in various fields, from web development to big data and mobile applications.

General Knowledge

Click Here