40 mins to read Technical interview questions and answers for freshers are questions that are typically asked in a technical interview for entry-level positions or for candidates who are just starting their careers in a particular field. These questions are designed to evaluate a candidate’s basic technical skills and knowledge, and may cover topics such as programming languages, data structures, algorithms, databases, and networking concepts.
Technical interview questions and answers for freshers
1. What is a variable?
A variable is a named memory location used to store data during program execution. It can hold various data types such as numbers, strings, and booleans.
2. What is the difference between a stack and a queue?
A stack is a data structure that operates on the principle of Last In First Out (LIFO), meaning the last item added to the stack is the first one to be removed. A queue, on the other hand, operates on the principle of First In First Out (FIFO), meaning the first item added to the queue is the first one to be removed.
3. What is a loop?
A loop is a programming construct that allows the repetition of a block of code until a certain condition is met. Common types of loops are the for loop, while loop, and do-while loop.
4. What is recursion?
Recursion is a technique in programming where a function calls itself repeatedly until a base case is reached. It is commonly used in solving problems that can be broken down into smaller subproblems.
5. What is object-oriented programming?
Object-oriented programming (OOP) is a programming paradigm that focuses on the use of objects and their interactions to design and develop software. It involves the use of classes, objects, inheritance, and encapsulation to create reusable code.
6. What is inheritance in OOP?
Inheritance is a mechanism in OOP that allows one class to inherit the properties and methods of another class. The class that inherits is called the subclass or derived class, and the class from which it inherits is called the superclass or base class.
7. What is polymorphism in OOP?
Polymorphism is a concept in OOP that allows objects of different classes to be treated as if they are of the same type. It is achieved through method overriding and method overloading.
8. What is the difference between a class and an object?
A class is a blueprint or template that defines the attributes and behaviors of an object. An object, on the other hand, is an instance of a class that has its own unique set of values for the attributes defined in the class.
9. What is a constructor in OOP?
A constructor is a special method in a class that is used to initialize the object’s attributes when it is created. It has the same name as the class and is called automatically when the object is created.
10. What is the difference between an abstract class and an interface?
An abstract class is a class that cannot be instantiated and is used as a base class for other classes. It can have abstract and non-abstract methods. An interface, on the other hand, is a collection of abstract methods that can be implemented by any class. A class can implement multiple interfaces, but can only inherit from one abstract class.
11. What is a pointer?
A pointer is a variable that stores the memory address of another variable. It allows a program to manipulate and access the value of a variable indirectly.
12. What is dynamic memory allocation?
Dynamic memory allocation is a mechanism that allows a program to request and use memory from the system at runtime. It is commonly used to allocate memory for data structures such as arrays and linked lists.
13. What is a data structure?
A data structure is a way of organizing and storing data in a computer program. It provides efficient methods for accessing and manipulating data.
14. What is a binary search?
A binary search is a search algorithm that operates on a sorted array or list. It works by repeatedly dividing the search interval in half until the target value is found or determined to be not present in the array.
15. What is a linked list?
A linked list is a data structure that consists of a sequence of nodes, each containing a value and a pointer to the next node in the sequence. It allows for efficient insertion and deletion of elements at any point in the list.
16. What is a stack overflow?
A stack overflow occurs when the call stack, a data structure used to manage function calls in a program, exceeds its maximum size. This can happen when a program has too many nested function calls or recursive calls.
17. What is a binary tree?
A binary tree is a data structure consisting of nodes, each with at most two child nodes, referred to as the left and right child. It is commonly used for sorting and searching algorithms.
18. What is a hash table?
A hash table is a data structure that stores key-value pairs in an array, with keys being mapped to indexes in the array using a hash function. It provides efficient methods for accessing and storing data.
19. What is a semaphore?
A semaphore is a synchronization primitive used in computer programming to control access to shared resources. It is a signaling mechanism that allows multiple processes to coordinate and communicate with each other.
20.What is a deadlock?
A deadlock is a situation that occurs when two or more processes are unable to proceed because each is waiting for the other to release a resource. This can result in a complete halt of the system.
21. What is a thread?
A thread is a lightweight process that can run concurrently with other threads within a program. It allows for parallel execution of tasks, which can improve performance and efficiency.
22. What is the difference between a process and a thread?
A process is an instance of a program that is executed by the operating system, with its own memory space and resources. A thread, on the other hand, is a unit of execution within a process that shares the process’s memory space and resources.
23. What is a deadlock?
A deadlock is a situation that occurs when two or more processes are unable to proceed because each is waiting for the other to release a resource. This can result in a complete halt of the system.
24. What is a virtual function in C++?
A virtual function is a function in C++ that is declared in a base class and can be overridden by a derived class. It allows for polymorphic behavior and dynamic binding.
25. What is the difference between a class method and an instance method?
A class method is a method that operates on the class itself rather than an instance of the class. It is declared with the keyword “static”. An instance method, on the other hand, operates on an instance of the class and is called using the dot notation.
26. What is a destructor in C++?
A destructor is a special method in C++ that is called when an object is destroyed. It is used to release resources allocated by the object during its lifetime.
27. What is an exception in Java?
An exception is a runtime error that occurs during the execution of a program. It represents an abnormal condition or situation that cannot be handled by the normal flow of control in the program. In Java, exceptions are objects that are thrown and caught by the program to handle such situations.
28. What is an abstract class in Java?
An abstract class is a class in Java that cannot be instantiated and is used as a base class for other classes. It contains one or more abstract methods that are not implemented in the abstract class but are implemented in its subclasses.
29. What is the difference between an interface and an abstract class in Java?
An interface is a collection of method declarations that a class can implement, whereas an abstract class is a class that cannot be instantiated and is used as a base class for other classes. An interface only contains method signatures, whereas an abstract class can contain concrete methods and instance variables.
30. What is a servlet in Java?
A servlet is a Java program that runs on a web server and processes requests from clients. It is used to create dynamic web content and is a key component of the Java Enterprise Edition (Java EE) platform.
31. What is a database?
A database is a collection of data that is organized in a way that allows for efficient storage, retrieval, and manipulation of data. It is commonly used in computer programs to store and manage large amounts of data.
32. What is SQL?
SQL (Structured Query Language) is a programming language used to manage and manipulate data in a relational database. It is used to create and modify database structures, as well as to retrieve and manipulate data stored in a database.
33. What is a primary key in a database?
A primary key is a column or set of columns in a database table that uniquely identifies each row in the table. It is used to ensure that each row in the table is unique and to enforce referential integrity between related tables.
34. What is normalization in database design?
Normalization is the process of organizing data in a database in a way that minimizes data redundancy and eliminates data anomalies. It involves breaking down a large table into smaller tables and establishing relationships between them.
35. What is a join in SQL?
A join in SQL is used to combine data from two or more tables in a database based on a related column or set of columns. There are several types of joins in SQL, including inner join, outer join, and cross join.
36. What is indexing in a database?
Indexing is the process of creating an index on one or more columns in a database table. An index allows for faster retrieval of data based on the indexed column, as the database can use the index to quickly locate the relevant rows.
37. What is a view in a database?
A view in a database is a virtual table that is created by combining data from one or more tables in the database. It is used to simplify complex queries and to provide a customized view of the data in the database.
38. What is a foreign key in a database?
A foreign key is a column or set of columns in a database table that refers to the primary key of another table in the database. It is used to establish a relationship between the two tables and to enforce referential integrity between them.
39. What is a transaction in a database?
A transaction in a database is a sequence of database operations that are performed as a single unit of work. It is used to ensure that all operations in the transaction are completed successfully, or else the entire transaction is rolled back to its original state.
40. What is a trigger in a database?
A trigger in a database is a special type of stored procedure that is automatically executed in response to a specific database event, such as the insertion, deletion, or modification of data in a table.
41. What is a deadlock in a database?
A deadlock in a database is a situation where two or more transactions are waiting for each other to release resources that they need to complete their work. This can result in a situation where none of the transactions can proceed, leading to a deadlock.
42. What is JDBC?
JDBC (Java Database Connectivity) is a Java API that is used to interact with relational databases. It provides a standard interface for connecting to a database, executing SQL statements, and processing the results.
43. What is Hibernate?
Hibernate is an open-source Java framework that provides an object-relational mapping (ORM) solution for mapping Java objects to relational databases. It simplifies the development of database-driven applications by abstracting away the details of database interaction.
44. What is Spring?
Spring is an open-source Java framework that is used to develop enterprise-level Java applications. It provides a comprehensive programming and configuration model for building modern Java applications.
45. What is Maven?
Maven is a build automation tool used primarily for Java projects. It is used to manage project dependencies, build and package the project, and deploy the project to a repository or server.
46. What is a thread in Java?
A thread in Java is a lightweight process that runs concurrently with other threads in the same process. It is used to execute code asynchronously and to improve the performance of multi-tasking applications.
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47. What is synchronization in Java?
Synchronization in Java is the process of controlling access to shared resources in a multi-threaded environment. It is used to prevent multiple threads from accessing shared resources at the same time, which can lead to data inconsistency and other problems.
48. What is a deadlock in Java?
A deadlock in Java is a situation where two or more threads are waiting for each other to release resources that they need to complete their work. This can result in a situation where none of the threads can proceed, leading to a deadlock.
49. What is a heap in Java?
A heap in Java is a region of memory used by the JVM to allocate objects at runtime. It is used to store objects that are created dynamically during the execution of a Java program.
50. What is garbage collection in Java?
Garbage collection in Java is the process of automatically freeing up memory that is no longer being used by a program. It is performed by the JVM and is used to prevent memory leaks and other memory-related problems in Java programs.
51. What is the difference between an abstract class and an interface in Java?
An abstract class is a class that cannot be instantiated and is used to provide a common base class for a hierarchy of related classes. An interface, on the other hand, defines a set of methods that a class must implement. While both abstract classes and interfaces can define abstract methods, an abstract class can also define concrete methods and instance variables, whereas an interface can only define constant values and method signatures.
52. What is the difference between a static method and an instance method in Java?
A static method is a method that is associated with a class rather than an instance of that class. It can be called directly on the class itself, without the need to create an instance of the class. An instance method, on the other hand, is a method that is associated with a specific instance of a class and can only be called on that instance.
53. What is the difference between an ArrayList and a LinkedList in Java?
An ArrayList is a resizable array that can hold objects of any type. It provides constant-time access to elements and is best suited for applications that require frequent access to elements in random order. A LinkedList, on the other hand, is a collection of nodes, where each node contains a reference to the next node in the list. It provides constant-time insertion and deletion of elements, but accessing elements requires traversing the list, which can be slow for large lists.
54. What is the difference between a HashMap and a TreeMap in Java?
A HashMap is an unordered collection of key-value pairs that provides constant-time access to elements based on their keys. A TreeMap, on the other hand, is a sorted map that maintains its elements in ascending order based on their keys. While a HashMap is best suited for applications that require fast access to elements, a TreeMap is best suited for applications that require elements to be sorted.
55. What is a singleton class in Java?
A singleton class is a class that can only be instantiated once and provides a global point of access to that instance. It is typically used for creating classes that maintain a single shared state throughout the lifetime of an application.
56. What is the difference between a final, finally, and finalize in Java?
A final is a keyword that is used to declare a constant variable or a method that cannot be overridden. A finally is a block of code that is used to ensure that a block of code is always executed, regardless of whether an exception is thrown or not. A finalize is a method that is called by the garbage collector when an object is about to be garbage collected.
57. What is polymorphism in Java?
Polymorphism in Java is the ability of an object to take on many forms. It allows objects of different classes to be treated as if they were of the same class, which makes code more flexible and reusable.
58. What is an abstract method in Java?
An abstract method in Java is a method that does not have an implementation in the class where it is declared. It is declared using the abstract keyword and is intended to be implemented by a subclass.
59. What is an exception in Java?
An exception in Java is an event that occurs during the execution of a program and disrupts the normal flow of control. It can be caused by a variety of factors, such as invalid input, resource exhaustion, or programming errors.
60. What is the purpose of the static keyword in Java?
The static keyword in Java is used to define a class-level variable or method. It allows the variable or method to be accessed directly on the class, rather than on an instance of the class.
61. What is method overloading in Java?
Method overloading in Java is a feature that allows a class to have multiple methods with the same name but different parameters. This allows the programmer to write code that is more concise and easier to read, as well as providing more flexibility and versatility to the class.
62. What is method overriding in Java?
Method overriding in Java is a feature that allows a subclass to provide a specific implementation of a method that is already defined in its superclass. This allows the subclass to modify the behavior of the method inherited from its superclass, while still maintaining the same method signature.
63. What is a package in Java?
A package in Java is a namespace that contains a set of related classes and interfaces. It provides a way to organize classes into logical groups and to avoid naming conflicts between classes from different libraries or applications.
64. What is an access modifier in Java?
An access modifier in Java is a keyword that specifies the level of access to a class, method, or variable. There are four access modifiers in Java: public, private, protected, and default. These modifiers determine whether other classes can access the class, method, or variable, and whether they can modify it.
65. What is a constructor in Java?
A constructor in Java is a special method that is used to initialize objects of a class. It is called when an object is created, and can be used to set the initial values of instance variables or to perform other initialization tasks.
66. What is an interface in Java?
An interface in Java is a collection of abstract methods and constants that can be implemented by a class. It provides a way to define a contract between different parts of an application, and allows objects of different classes to be treated as if they were of the same type.
67. What is inheritance in Java?
Inheritance in Java is a mechanism that allows a subclass to inherit the properties and methods of its superclass. This allows the subclass to reuse code from its superclass, and to add new functionality without duplicating code.
68. What is encapsulation in Java?
Encapsulation in Java is the process of hiding the internal details of an object from the outside world, and providing a public interface to access and modify the object’s state. This helps to maintain the integrity of the object’s data and to prevent unintended modifications.
69. What is a thread in Java?
A thread in Java is a lightweight unit of execution that runs concurrently with other threads within the same program. Threads allow multiple tasks to be performed simultaneously, and can improve the responsiveness and performance of an application.
70. What is the difference between an error and an exception in Java?
An error in Java is a serious problem that typically cannot be handled by the application. Examples of errors include OutOfMemoryError and StackOverflowError. An exception, on the other hand, is a problem that can be handled by the application, and is typically caused by invalid input, resource exhaustion, or programming errors. Examples of exceptions include NullPointerException and ArrayIndexOutOfBoundsException.
Checked exceptions in Java are exceptions that are checked at compile-time, and must be either caught or declared in the method signature. Examples of checked exceptions include IOException and SQLException. Unchecked exceptions, on the other hand, are exceptions that are not checked at compile-time, and do not need to be caught or declared. Examples of unchecked exceptions include NullPointerException and ArrayIndexOutOfBoundsException.
72. What is a static variable in Java?
A static variable in Java is a variable that belongs to a class rather than to any particular instance of the class. This means that the variable is shared by all instances of the class, and can be accessed using the class name rather than an object reference.
73. What is a static method in Java?
A static method in Java is a method that belongs to a class rather than to any particular instance of the class. This means that the method can be called using the class name rather than an object reference, and can be accessed without creating an instance of the class.
74. What is the final keyword in Java?
The final keyword in Java is used to declare a variable, method, or class as immutable, meaning that its value cannot be changed once it has been set. A final variable cannot be reassigned, a final method cannot be overridden, and a final class cannot be extended.
75. What is a synchronized method in Java?
A synchronized method in Java is a method that is protected by a lock, which prevents multiple threads from accessing the method simultaneously. This is used to prevent race conditions and ensure that the method behaves correctly in a multithreaded environment.
76. What is a deadlock in Java?
A deadlock in Java occurs when two or more threads are blocked, waiting for each other to release resources that they need in order to continue executing. This can result in a situation where none of the threads can proceed, and the program appears to be frozen.
77. What is the difference between the equals() method and the == operator in Java?
The equals() method in Java is used to compare the values of two objects for equality, while the == operator is used to compare the memory addresses of two objects. In other words, equals() compares the contents of two objects, while == compares their references.
78. What is a hash table in Java?
A hash table in Java is a data structure that provides fast access to key-value pairs, based on the hash code of the key. It uses an array to store the key-value pairs, and a hashing function to map the keys to indices in the array.
79. What is a linked list in Java?
A linked list in Java is a data structure that consists of a sequence of nodes, each of which contains a data element and a reference to the next node in the list. This allows for efficient insertion and deletion of elements, but may result in slower access times than other data structures such as arrays.
80. What is a stack in Java?
A stack in Java is a data structure that allows elements to be inserted and removed from only one end, known as the top of the stack. It follows the Last-In-First-Out (LIFO) principle, meaning that the last element added to the stack is the first one to be removed.
A queue in Java is a data structure that allows elements to be inserted at one end, known as the rear of the queue, and removed from the other end, known as the front of the queue. It follows the First-In-First-Out (FIFO) principle, meaning that the first element added to the queue is the first one to be removed.
82. What is polymorphism in Java?
Polymorphism in Java is the ability of an object to take on many forms. This can be achieved through method overloading or method overriding. Method overloading allows multiple methods with the same name but different parameters to be defined within the same class, while method overriding allows a subclass to provide a specific implementation of a method that is already defined in its superclass.
83. What is inheritance in Java?
Inheritance in Java is a mechanism by which a new class is created from an existing class, with the new class inheriting the properties and methods of the existing class. This allows for code reuse and the creation of hierarchies of related classes.
84. What is encapsulation in Java?
Encapsulation in Java is the practice of hiding the implementation details of a class from other classes. This is typically achieved by using access modifiers to control access to the class’s variables and methods.
85. What is abstraction in Java?
Abstraction in Java is the process of identifying the essential features of a class or interface, while ignoring the implementation details. This allows for the creation of generalizations that can be applied to a wide variety of specific cases.
86. What is a constructor in Java?
A constructor in Java is a special method that is used to create and initialize an object of a class. It has the same name as the class, and is called automatically when an object is created.
87. What is an interface in Java?
An interface in Java is a collection of abstract methods that define a set of behaviors that a class can implement. It is used to define a contract between a class and the outside world, and can be used to achieve polymorphism and loose coupling.
88. What is the difference between an abstract class and an interface in Java?
An abstract class in Java is a class that cannot be instantiated, and is typically used to define a base class that other classes can inherit from. It can contain both abstract and non-abstract methods, and can have instance variables. An interface, on the other hand, is a collection of abstract methods that define a set of behaviors that a class can implement. It cannot contain any implementation code, and is used to define a contract between a class and the outside world.
89. What is a package in Java?
A package in Java is a mechanism for organizing related classes and interfaces into a single namespace. It helps to prevent naming conflicts and makes it easier to manage large projects.
90. What is a JAR file in Java?
A JAR (Java ARchive) file in Java is a file format used to distribute a set of Java classes and associated resources as a single unit. It can be used to simplify the distribution and deployment of Java applications, and can be run using the Java Virtual Machine (JVM).
A servlet in Java is a Java program that runs on a web server and processes incoming requests and produces responses. It is a server-side component that can be used to handle web-based requests and generate dynamic content.
92. What is a JSP in Java?
A JSP (JavaServer Pages) in Java is a technology that allows for the creation of dynamic web pages by combining HTML, Java code, and JSP elements. It is a server-side component that can be used to generate dynamic content in response to user requests.
93. What is JDBC in Java?
JDBC (Java Database Connectivity) in Java is a standard API (Application Programming Interface) that allows Java programs to access and manipulate data stored in databases. It provides a set of classes and interfaces that enable Java applications to interact with databases in a platform-independent way.
94. What is the difference between the == operator and the equals() method in Java?
The == operator in Java is used to compare the reference values of two objects. It returns true if the two objects refer to the same memory location, and false otherwise. The equals() method, on the other hand, is used to compare the content or value of two objects. It returns true if the two objects have the same content, and false otherwise.
95. What is the difference between a checked and an unchecked exception in Java?
A checked exception in Java is an exception that must be declared in the method signature or handled with a try-catch block. Examples include IOException and SQLException. An unchecked exception, on the other hand, is an exception that does not need to be declared in the method signature or handled with a try-catch block. Examples include NullPointerException and ArithmeticException.
96. What is the difference between a static and non-static method in Java?
A static method in Java is a method that belongs to the class rather than the instance of the class. It can be called without creating an instance of the class. A non-static method, on the other hand, is a method that belongs to the instance of the class, and can only be called on an instance of the class.
97. What is the difference between an abstract class and a concrete class in Java?
An abstract class in Java is a class that cannot be instantiated, and is typically used to define a base class that other classes can inherit from. It can contain both abstract and non-abstract methods, and can have instance variables. A concrete class, on the other hand, is a class that can be instantiated, and can be used to create objects.
98.What is the difference between a private and a protected method in Java?
A private method in Java is a method that can only be accessed within the same class in which it is defined. A protected method, on the other hand, is a method that can be accessed within the same class, as well as by subclasses and classes in the same package.
99. What is the difference between a final class and a final method in Java?
A final class in Java is a class that cannot be subclassed or extended. A final method, on the other hand, is a method that cannot be overridden by a subclass.
100. What is the difference between a stack and a queue in Java?
A stack in Java is a data structure that follows the Last-In-First-Out (LIFO) principle, meaning that the last element added to the stack is the first one to be removed. A queue, on the other hand, follows the First-In-First-Out (FIFO) principle, meaning that the first element added to the queue is the first one to be removed.
A package in Java is a way of organizing related classes and interfaces. It provides a namespace for the classes and interfaces, which helps to avoid naming conflicts with classes and interfaces from other packages.
102. What is the access modifier “default” in Java?
The “default” access modifier in Java is used when no access modifier is specified. It is also known as the package-private access modifier, and it allows access to the member within the same package. It is more restrictive than the “protected” access modifier, which allows access to the member within the same package and by subclasses.
103. What is the difference between a StringBuffer and StringBuilder in Java?
A StringBuffer and StringBuilder in Java are both classes that represent a mutable sequence of characters. The difference between them is that StringBuffer is synchronized, meaning that it is thread-safe and can be accessed by multiple threads at the same time without any problems. StringBuilder, on the other hand, is not synchronized, meaning that it is not thread-safe, but it is faster than StringBuffer in single-threaded applications.
104. What is a static block in Java?
A static block in Java is a block of code that is executed when the class is loaded into memory, before any object of the class is created. It is used to initialize static variables or to perform any other initialization tasks that need to be done before the class is used.
105. What is a constructor in Java?
A constructor in Java is a special method that is used to initialize an object when it is created. It has the same name as the class and no return type. It can take parameters, which are used to initialize the instance variables of the object.
106. What is the difference between a constructor and a method in Java?
A constructor in Java is a special method that is used to initialize an object when it is created. It has the same name as the class and no return type. A method, on the other hand, is a general-purpose method that can be used to perform any operation on an object. It has a name, return type, and parameters, and can be called on an object after it has been created.
107. What is the final keyword in Java?
The final keyword in Java is used to indicate that a variable, method, or class cannot be modified or extended. A final variable cannot be reassigned, a final method cannot be overridden by a subclass, and a final class cannot be extended.
108. What is the difference between an interface and an abstract class in Java?
An interface in Java is a collection of method signatures, but does not provide any implementation. It is used to define a contract that a class must implement. An abstract class, on the other hand, is a class that cannot be instantiated, and is typically used to define a base class that other classes can inherit from. It can contain both abstract and non-abstract methods, and can have instance variables.
109. What is a thread in Java?
A thread in Java is a separate path of execution within a program. It allows for concurrent execution of different parts of a program, which can improve performance and responsiveness.
110. What is the difference between the wait() and sleep() methods in Java?
The wait() method in Java is used to make a thread wait until it is notified by another thread or until a certain amount of time has passed. It can only be called within a synchronized block. The sleep() method, on the other hand, is used to make a thread sleep for a certain amount of time. It does not release the lock on the object, so other threads cannot access the object while the thread is sleeping.
Synchronization in Java is the process of controlling the access to shared resources or critical sections of code by multiple threads. It ensures that only one thread can access the shared resource at a time, preventing race conditions and other concurrency issues.
112. What is a deadlock in Java?
A deadlock in Java is a situation where two or more threads are blocked waiting for each other to release resources that they are holding. This can result in a situation where none of the threads can continue, and the program becomes unresponsive.
113. What is a finalizer in Java?
A finalizer in Java is a method that is called by the garbage collector before an object is destroyed. It is used to perform any final cleanup tasks that need to be done before the object is removed from memory.
114. What is the difference between checked and unchecked exceptions in Java?
Checked exceptions in Java are exceptions that the compiler requires you to handle or declare in the method signature. Unchecked exceptions, on the other hand, are exceptions that do not need to be handled or declared. They are usually caused by programming errors, such as null pointer exceptions or array index out of bounds exceptions.
115. What is the purpose of the “this” keyword in Java?
The “this” keyword in Java is used to refer to the current object. It is typically used to disambiguate between instance variables and parameters with the same name, or to call one constructor from another constructor in the same class.
116. What is a lambda expression in Java?
A lambda expression in Java is a way of expressing a block of code as an object. It is used to create instances of functional interfaces, which are interfaces that define a single abstract method. Lambda expressions can be used to provide a concise and expressive way of writing code.
117. What is a stream in Java?
A stream in Java is a sequence of elements that can be processed in a functional style. It allows for operations such as filtering, mapping, and reducing to be performed on collections of objects in a concise and expressive way.
118. What is the difference between a stream and a collection in Java?
A collection in Java is a data structure that holds a group of objects, whereas a stream is a sequence of objects that can be processed in a functional style. A collection is typically used to store objects for later access or modification, whereas a stream is used to perform operations on a group of objects without modifying the original collection.
119. What is the purpose of the “super” keyword in Java?
The “super” keyword in Java is used to refer to the superclass of the current class. It can be used to call the constructor of the superclass, or to access the methods or variables of the superclass.
120. What is a reflection in Java?
Reflection in Java is the ability of a program to examine and modify its own structure and behavior at runtime. It allows for dynamic loading of classes, introspection of classes and objects, and manipulation of objects and classes at runtime.
A package in Java is a way of organizing related classes and interfaces into a single unit. It helps to avoid naming conflicts between classes in different packages, and allows for better organization and management of large code bases.
122. What is a constructor in Java?
A constructor in Java is a special method that is used to initialize objects of a class. It is called when an object is created, and is used to set the initial values of the object’s instance variables.
123. What is polymorphism in Java?
Polymorphism in Java is the ability of an object to take on many forms. It allows for a single method or class to be used with objects of different types, as long as they share a common interface or superclass.
124. What is method overloading in Java?
Method overloading in Java is the ability to define multiple methods with the same name in a single class. The methods must differ in their parameter lists, allowing for different versions of the method to be called depending on the arguments passed to it.
125. What is method overriding in Java?
Method overriding in Java is the ability to define a method in a subclass that has the same name, return type, and parameters as a method in its superclass. The overridden method in the superclass is replaced by the method in the subclass when the method is called on an object of the subclass.
126. What is an interface in Java?
An interface in Java is a collection of abstract methods and constant values that can be implemented by a class. It defines a set of methods that a class must implement, allowing for multiple classes to share common behavior without being related by inheritance.
127. What is an abstract class in Java?
An abstract class in Java is a class that cannot be instantiated, and is typically used as a base class for other classes to inherit from. It can contain both abstract and concrete methods, and may define abstract methods that must be implemented by its subclasses.
128. What is the difference between an abstract class and an interface in Java?
An abstract class in Java can contain both abstract and concrete methods, whereas an interface can only contain abstract methods and constant values. An abstract class can be extended by a single class, whereas a class can implement multiple interfaces. An abstract class is typically used to define a base class for other classes to inherit from, whereas an interface is used to define a set of methods that a class must implement.
129. What is the difference between static and non-static methods in Java?
A static method in Java is a method that belongs to the class itself, rather than to a specific instance of the class. It can be called without creating an instance of the class. A non-static method, on the other hand, is a method that is called on a specific instance of the class.
130. What is the purpose of the “static” keyword in Java?
The “static” keyword in Java is used to declare a variable or method as belonging to the class itself, rather than to a specific instance of the class. It allows for the variable or method to be called without creating an instance of the class.
131. What is a multi-threading in Java?
Multi-threading in Java is the ability of a program to execute multiple threads of execution concurrently. It allows for multiple tasks to be performed at the same time, improving the overall performance and responsiveness of the program.
132. What is a daemon thread in Java?
A daemon thread in Java is a thread that runs in the background, providing a service to other threads. It is typically used to perform tasks that do not require user interaction, such as garbage collection or background I/O.
134. What is the purpose of the “volatile” keyword in Java?
The “volatile” keyword in Java is used to indicate that a variable’s value may be modified by multiple threads. When a variable is declared volatile, the compiler and runtime system ensure that all accesses to the variable are done in a way that is consistent with the Java Memory Model, which specifies the ordering of reads and writes to shared memory in a multi-threaded environment. This ensures that changes made to the variable by one thread are immediately visible to other threads that access the variable, preventing inconsistent or incorrect behavior due to concurrent modifications.
A Java Bean is a Java class that follows certain naming and coding conventions, allowing it to be easily manipulated by visual development tools. It typically has a no-argument constructor, private member variables with public getter and setter methods, and implements the Serializable interface.
136. What is a final class in Java?
A final class in Java is a class that cannot be subclassed. It is typically used to prevent the class from being modified or extended, ensuring that its behavior remains consistent.
137. What is a final variable in Java?
A final variable in Java is a variable that cannot be reassigned once it has been initialized. It is typically used to define constants or to prevent the accidental modification of a variable.
138. What is the difference between public, private, and protected access modifiers in Java?
Public, private, and protected are access modifiers used in Java to control the visibility of class members. Public members can be accessed from anywhere, private members can only be accessed from within the same class, and protected members can be accessed from within the same package or from subclasses in other packages.
139. What is a try-catch block in Java?
A try-catch block in Java is used to handle exceptions that may occur during program execution. The code that may throw an exception is placed in the try block, and any exceptions that are thrown are caught and handled in the catch block.
140. What is a finally block in Java?
A finally block in Java is used to ensure that a block of code is executed regardless of whether an exception is thrown or not. It is typically used to release resources or to perform cleanup tasks.
141. What is a static block in Java?
A static block in Java is a block of code that is executed when a class is loaded into memory. It is typically used to initialize static variables or to perform other one-time setup tasks.
142. What is a package-private access modifier in Java?
Package-private is an access modifier in Java that allows class members to be accessed only from within the same package. It is used to control the visibility of class members and to prevent them from being accessed from outside the package.
143. What is the purpose of the “this” keyword in Java?
The “this” keyword in Java is used to refer to the current object. It is typically used to distinguish between instance variables and local variables with the same name, or to pass the current object as a parameter to a method.
144. What is the purpose of the “super” keyword in Java?
The “super” keyword in Java is used to refer to the parent class of the current class. It is typically used to call the constructor or methods of the parent class, or to access parent class members that have been overridden in the child class.
145. What is the difference between an ArrayList and a LinkedList in Java?
An ArrayList in Java is a dynamic array that can be resized as needed. It provides constant-time access to individual elements, but slower insertion and deletion times as elements must be shifted to maintain the order of the array.
A LinkedList in Java is a linked list data structure that provides constant-time insertion and deletion of elements, but slower access times as elements must be traversed sequentially to access them.
146. What is a stream in Java?
A stream in Java is a sequence of elements that can be processed in parallel or sequentially. It is typically used to perform operations on collections, such as filtering, sorting, or mapping elements.
147. What is the purpose of the “map” method in Java streams?
The “map” method in Java streams is used to transform the elements of a stream using a specified function. It takes a Function as a parameter, which is applied to each element of the stream, and returns a new stream containing
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