Interview Prep Flashcards

Question

What is the Application Context definition?

Answer 1

In general, the application context has a similar definition to the bean factory. It loads bean definitions, wires beans together, and dispenses them if required. Also, it provides a generic way to load file resources, specific events to the beans defined as listeners, as well as means for resolving text messages using various languages.

Answer 2

JDBC (also known as Java Database Connectivity) stands for the Java API, responsible for the connection to a database, queries, and commands issuing as well as receiving the result sets processed by the database. Basically, it enables developers to switch between the databases without having to underlie the specific features of a particular database.

Answer 3

The controllers of the Spring MVC framework enable access to the app behavior programmers typically define via the service interface. They analyze the user’s query and convert it into the specific model user can perceive by the view component. The controllers in Spring are implemented only in the abstract way, thus allowing developers to create a wide range of different controllers.

Answer 4

CI is a DevOps software development practice that is used to merge the code changes made by different developers in the central repository in order to run automated builds and tests. CI should build code multiple times a day in order to timely detect any issue and identify its cause.

Answer 5

Java and C++ are both object-oriented programming languages, but they have some key differences. Platform independence: Java is a platform-independent language, while C++ is a platform-dependent language. This means that Java code can run on any platform that has a Java virtual machine (JVM), while C++ code can only run on the platform that it was compiled for. Memory management: Java uses automatic memory management, while C++ requires manual memory management. This means that Java programmers do not need to worry about allocating and freeing memory, while C++ programmers need to be careful to manage memory correctly to avoid memory leaks. Safety: Java is a safer language than C++. This is because Java has built-in security features that help to protect applications from malicious code. For example, Java does not allow direct access to the operating system, which makes it more difficult for attackers to exploit security vulnerabilities. Performance: Java is typically not as fast as C++. This is because Java uses a virtual machine, which adds an extra layer of abstraction between the code and the hardware. However, Java applications are typically more portable and secure than C++ applications.

Answer 6

It stands for Java Development Kit. It is the tool necessary to compile, document and package Java programs. It contains JRE + development tools.

Answer 7

It stands for Java Runtime Environment. JRE refers to a runtime environment in which Java bytecode can be executed. It’s an implementation of the JVM which physically exists.

Answer 8

It stands for Java Virtual Machine. It is an abstract machine. It is a specification that provides a run-time environment in which Java bytecode can be executed. JVM follows three notations: Specification, Implementation, and Runtime Instance.

Answer 9

main() in Java is the entry point for any Java program. It is always written as public static void main(String[] args). public: Public is an access modifier, which is used to specify who can access this method. Public means that this Method will be accessible by any Class. static: It is a keyword in java which identifies it is class-based. main() is made static in Java so that it can be accessed without creating the instance of a Class. In case, main is not made static then the compiler will throw an error as main() is called by the JVM before any objects are made and only static methods can be directly invoked via the class. void: It is the return type of the method. Void defines the method which will not return any value. main: It is the name of the method which is searched by JVM as a starting point for an application with a particular signature only. It is the method where the main execution occurs. String args[]: It is the parameter passed to the main method.

Answer 10

The Java ClassLoader subset of JVM loads class files. The classloader loads Java programs first. Three classloaders are built into Java: Bootstrap ClassLoader Extension ClassLoader System/Application ClassLoader

Answer 11

Java is not 100% Object-oriented because it makes use of eight primitive data types such as boolean, byte, char, int, float, double, long, short which are not objects.

Answer 12

boolean, byte, char, double, int, float, long, short

Answer 13

Wrapper classes convert the Java primitives into the reference types (objects). Every primitive data type has a class dedicated to it. These are known as wrapper classes because they “wrap” the primitive data type into an object of that class. Refer to the below image which displays different primitive type, wrapper class and constructor argument.

Answer 14

In Java, constructor refers to a block of code which is used to initialize an object. It must have the same name as that of the class. Also, it has no return type and it is automatically called when an object is created. There are two types of constructors: Default Constructor: In Java, a default constructor is the one which does not take any inputs. In other words, default constructors are the no argument constructors which will be created by default in case you no other constructor is defined by the user. Its main purpose is to initialize the instance variables with the default values. Also, it is majorly used for object creation. Parameterized Constructor: The parameterized constructor in Java, is the constructor which is capable of initializing the instance variables with the provided values. In other words, the constructors which take the arguments are called parameterized constructors.

Answer 15

Singleton class is a class whose only one instance can be created at any given time, in one JVM. A class can be made singleton by making its constructor private.

Answer 16

Equals() method is defined in Object class in Java and used for checking equality of two objects defined by business logic. “==” or equality operator in Java is a binary operator provided by Java programming language and used to compare primitives and objects. public boolean equals(Object o) is the method provided by the Object class. The default implementation uses == operator to compare two objects. For example: method can be overridden like String class. equals() method is used to compare the values of two objects.

Answer 17

In Java, the super keyword is a reference variable that refers to an immediate parent class object. When you create a subclass instance, you’re also creating an instance of the parent class, which is referenced to by the super reference variable. The uses of the Java super Keyword are- To refer to an immediate parent class instance variable, use super. The keyword super can be used to call the method of an immediate parent class. Super() can be used to call the constructor of the immediate parent class.

Answer 18

When we create a string using new(), a new object is created. Whereas, if we create a string using the string literal syntax, it may return an already existing object with the same name.

Answer 19

Stack memory is used only by one thread of execution. Stack memory can’t be accessed by other threads. Exists until the end of execution of the thread. Stack memory only contains local primitive and reference variables to objects in heap space.

Answer 20

Heap memory is used by all the parts of the application. Objects stored in the heap are globally accessible. Memory management is based on the generation associated with each object. Heap memory lives from the start till the end of application execution. Whenever an object is created, it’s always stored in the Heap space.

Answer 21

Packages in Java, are the collection of related classes and interfaces which are bundled together. By using packages, developers can easily modularize the code and optimize its reuse. Also, the code within the packages can be imported by other classes and reused. Below I have listed down a few of its advantages: Packages help in avoiding name clashes They provide easier access control on the code Packages can also contain hidden classes which are not visible to the outer classes and only used within the package Creates a proper hierarchical structure which makes it easier to locate the related classes

Answer 22

JIT stands for Just-In-Time compiler in Java. It is a program that helps in converting the Java bytecode into instructions that are sent directly to the processor. By default, the JIT compiler is enabled in Java and is activated whenever a Java method is invoked. The JIT compiler then compiles the bytecode of the invoked method into native machine code, compiling it “just in time” to execute. Once the method has been compiled, the JVM summons the compiled code of that method directly rather than interpreting it. This is why it is often responsible for the performance optimization of Java applications at the run time.

Answer 23

In Java, access modifiers are special keywords which are used to restrict the access of a class, constructor, data member and method in another class. Java supports four types of access modifiers: Default Private Protected Public

Answer 24

An object is a real-world entity that has a state and behavior. An object has three characteristics: State Behavior Identity An object is created using the ‘new’ keyword. For example: ClassName obj = new ClassName();

Answer 25

Object-Oriented Programming or OOPs is a programming style that is associated with concepts like: Inheritance: Inheritance is a process where one class acquires the properties of another. Encapsulation: Encapsulation in Java is a mechanism of wrapping up the data and code together as a single unit. Abstraction: Abstraction is the methodology of hiding the implementation details from the user and only providing the functionality to the users. Polymorphism: Polymorphism is the ability of a variable, function or object to take multiple forms.

Answer 26

In Java, a local variable is typically used inside a method, constructor, or a block and has only local scope. Thus, this variable can be used only within the scope of a block. The best benefit of having a local variable is that other methods in the class won’t be even aware of that variable. Whereas, an instance variable in Java, is a variable which is bounded to its object itself. These variables are declared within a class, but outside a method. Every object of that class will create it’s own copy of the variable while using it. Thus, any changes made to the variable won’t reflect in any other instances of that class and will be bound to that particular instance only.

Answer 27

Used to initialize the state of an object Do not have any return type Is invoked implicitly A default constructor is provided by the compiler if the class has none Constructor name must always be the same as the class name

Answer 28

final is a special keyword in Java that is used as a non-access modifier. A final variable can be used in different contexts such as: final variable When the final keyword is used with a variable then its value can’t be changed once assigned. In case the no value has been assigned to the final variable then using only the class constructor a value can be assigned to it. final method When a method is declared final then it can’t be overridden by the inheriting class. final class When a class is declared as final in Java, it can’t be extended by any subclass class but it can extend other class

Answer 29

this() represents the current instance of a class Used to call the default constructor of the same class Used to access methods of the current class Used for pointing the current class instance Must be the first line of a block

Answer 30

super() represents the current instance of a parent/base class Used to call the default constructor of the parent/base class Used to access methods of the base class Used for pointing the superclass instance Must be the first line of a block

Answer 31

In Java, string objects are immutable in nature which simply means once the String object is created its state cannot be modified. Whenever you try to update the value of that object instead of updating the values of that particular object, Java creates a new string object. Java String objects are immutable as String objects are generally cached in the String pool. Since String literals are usually shared between multiple clients, action from one client might affect the rest. It enhances security, caching, synchronization, and performance of the application.

Answer 32

Arrays can contain primitive data types as well as objects. Arrays Cannot contain values of different data types. Arraylists can contain only objects, no primitive data types are allowed Arraylists Can contain values of different data types.

Answer 33

In Java, Map is an interface of Util package which maps unique keys to values. The Map interface is not a subset of the main Collection interface and thus it behaves little different from the other collection types. Below are a few of the characteristics of Map interface: Map doesn’t contain duplicate keys. Each key can map at max one value.

Answer 34

In Java, the collection is a framework that acts as an architecture for storing and manipulating a group of objects. Using Collections you can perform various tasks like searching, sorting, insertion, manipulation, deletion, etc. Java collection framework includes the following: Interfaces Classes Methods

Answer 35

Polymorphism is briefly described as “one interface, many implementations”. Polymorphism is a characteristic of being able to assign a different meaning or usage to something in different contexts – specifically, to allow an entity such as a variable, a function, or an object to have more than one form. There are two types of polymorphism: Compile time polymorphism Run time polymorphism Compile time polymorphism is method overloading whereas Runtime time polymorphism is done using inheritance and interface.

Answer 36

Abstraction refers to the quality of dealing with ideas rather than events. It basically deals with hiding the details and showing the essential things to the user. Thus you can say that abstraction in Java is the process of hiding the implementation details from the user and revealing only the functionality to them. Abstraction can be achieved in two ways: Abstract Classes (0-100% of abstraction can be achieved) Interfaces (100% of abstraction can be achieved)

Answer 37

An interface in Java is a blueprint of a class or you can say it is a collection of abstract methods and static constants. In an interface, each method is public and abstract but it does not contain any constructor. Thus, interface basically is a group of related methods with empty bodies. Example:

Answer 38

An interface cannot provide any code at all, just the signature A Class may implement several interfaces All methods of an Interface are abstract An Interface cannot have instance variables An Interface visibility must be public (or) none f we add a new method to an Interface then we have to track down all the implementations of the interface and define implementation for the new method An Interface cannot contain constructors

Answer 39

Inheritance in Java is the concept where the properties of one class can be inherited by the other. It helps to reuse the code and establish a relationship between different classes. Inheritance is performed between two types of classes: Parent class (Super or Base class) Child class (Subclass or Derived class) A class which inherits the properties is known as Child Class whereas a class whose properties are inherited is known as Parent class.

Answer 40

Java supports four types of inheritance which are: Single Inheritance: In single inheritance, one class inherits the properties of another i.e there will be only one parent as well as one child class. Multilevel Inheritance: When a class is derived from a class which is also derived from another class, i.e. a class having more than one parent class but at different levels, such type of inheritance is called Multilevel Inheritance. Hierarchical Inheritance: When a class has more than one child classes (subclasses) or in other words, more than one child classes have the same parent class, then such kind of inheritance is known as hierarchical. Hybrid Inheritance: Hybrid inheritance is a combination of two or more types of inheritance.

Answer 41

In Method Overloading, Methods of the same class shares the same name but each method must have a different number of parameters or parameters having different types and order. Method Overloading is to “add” or “extend” more to the method’s behavior. It is a compile-time polymorphism. The methods must have a different signature. It may or may not need inheritance in Method Overloading.

Answer 42

In Method Overriding, the subclass has the same method with the same name and exactly the same number and type of parameters and same return type as a superclass. Method Overriding is to “Change” existing behavior of the method. It is a run time polymorphism. The methods must have the same signature. It always requires inheritance in Method Overriding.

Answer 43

You cannot override a private or static method in Java. If you create a similar method with the same return type and same method arguments in child class then it will hide the superclass method; this is known as method hiding. Similarly, you cannot override a private method in subclass because it’s not accessible there. What you can do is create another private method with the same name in the child class.

Answer 44

If a child class inherits the property from multiple classes is known as multiple inheritance. Java does not allow to extend multiple classes. The problem with multiple inheritance is that if multiple parent classes have the same method name, then at runtime it becomes difficult for the compiler to decide which method to execute from the child class. Therefore, Java doesn’t support multiple inheritance. The problem is commonly referred to as Diamond Problem.

Answer 45

Encapsulation is a mechanism where you bind your data(variables) and code(methods) together as a single unit. Here, the data is hidden from the outer world and can be accessed only via current class methods. This helps in protecting the data from any unnecessary modification. We can achieve encapsulation in Java by: Declaring the variables of a class as private. Providing public setter and getter methods to modify and view the values of the variables.

Answer 46

Association is a relationship where all object have their own lifecycle and there is no owner. Let’s take the example of Teacher and Student. Multiple students can associate with a single teacher and a single student can associate with multiple teachers but there is no ownership between the objects and both have their own lifecycle. These relationships can be one to one, one to many, many to one and many to many.

Answer 47

An aggregation is a specialized form of Association where all object has their own lifecycle but there is ownership and child object can not belong to another parent object. Let’s take an example of Department and teacher. A single teacher can not belong to multiple departments, but if we delete the department teacher object will not destroy.

Answer 48

Composition is again a specialized form of Aggregation and we can call this as a “death” relationship. It is a strong type of Aggregation. Child object does not have their lifecycle and if parent object deletes all child object will also be deleted. Let’s take again an example of a relationship between House and rooms. House can contain multiple rooms there is no independent life of room and any room can not belongs to two different houses if we delete the house room will automatically delete.

Answer 49

In Java, a marker interface is an interface that does not declare any methods or fields. Its sole purpose is to mark or tag a class as having a certain characteristic or capability. By implementing a marker interface, a class indicates that it possesses specific behavior or qualifies for a particular treatment. Marker interfaces are purely a convention and serve as a form of metadata. They provide a way for developers or frameworks to identify classes that meet certain criteria without requiring any additional methods or fields.

Answer 50

Object cloning in Java is the process of creating an exact copy of an object. It basically means the ability to create an object with a similar state as the original object. To achieve this, Java provides a method clone() to make use of this functionality. This method creates a new instance of the class of the current object and then initializes all its fields with the exact same contents of corresponding fields. To object clone(), the marker interface java.lang.Cloneable must be implemented to avoid any runtime exceptions. One thing you must note is Object clone() is a protected method, thus you need to override it.

Answer 51

Copy constructor is a member function that is used to initialize an object using another object of the same class. Though there is no need for copy constructor in Java since all objects are passed by reference. Moreover, Java does not even support automatic pass-by-value.

Answer 52

In Java, constructor overloading is a technique of adding any number of constructors to a class each having a different parameter list. The compiler uses the number of parameters and their types in the list to differentiate the overloaded constructors.

Answer 53

Java Servlet is server-side technologies to extend the capability of web servers by providing support for dynamic response and data persistence. The javax.servlet and javax.servlet.http packages provide interfaces and classes for writing our own servlets. All servlets must implement the javax.servlet.Servlet interface, which defines servlet lifecycle methods. When implementing a generic service, we can extend the GenericServlet class provided with the Java Servlet API. The HttpServlet class provides methods, such as doGet() and doPost(), for handling HTTP-specific services. Most of the times, web applications are accessed using HTTP protocol and thats why we mostly extend HttpServlet class. Servlet API hierarchy is shown in below image.

Answer 54

RequestDispatcher interface is used to forward the request to another resource that can be HTML, JSP or another servlet in same application. We can also use this to include the content of another resource to the response. There are two methods defined in this interface: 1.void forward() 2.void include()

Answer 55

Servlet is loaded Servlet is instantiated Servlet is initialized Service the request Servlet is destroyed

Answer 56

The DriverManager class manages the registered drivers. It can be used to register and unregister drivers. It provides factory method that returns the instance of Connection.

Answer 57

The Connection interface maintains a session with the database. It can be used for transaction management. It provides factory methods that returns the instance of Statement, PreparedStatement, CallableStatement and DatabaseMetaData.

Answer 58

he important annotations are: @Required @Autowired @Qualifier @Resource @PostConstruct @PreDestroy

Answer 59

Beans are objects that form the backbone of a Spring application. They are managed by the Spring IoC container. In other words, a bean is an object that is instantiated, assembled, and managed by a Spring IoC container. There are five Scopes defined in Spring beans.

Answer 60

Singleton: Only one instance of the bean will be created for each container. This is the default scope for the spring beans. While using this scope, make sure spring bean doesn’t have shared instance variables otherwise it might lead to data inconsistency issues because it’s not thread-safe. Prototype: A new instance will be created every time the bean is requested. Request: This is same as prototype scope, however it’s meant to be used for web applications. A new instance of the bean will be created for each HTTP request. Session: A new bean will be created for each HTTP session by the container. Global-session: This is used to create global session beans for Portlet applications.

Answer 61

n Spring framework, the scope of a bean determines the lifecycle and visibility of the bean instance within the container. You can set the scope of a Spring bean using the `@Scope` annotation or the XML configuration. To set the scope using the `@Scope` annotation, you can specify it on the bean class or the bean definition method within a configuration class. Here’s an example:

Answer 62

@Controller – for controller classes in Spring MVC project. @RequestMapping – for configuring URI mapping in controller handler methods. This is a very important annotation, so you should go through Spring MVC RequestMapping Annotation Examples @ResponseBody – for sending Object as response, usually for sending XML or JSON data as response. @PathVariable – for mapping dynamic values from the URI to handler method arguments. @Autowired – for autowiring dependencies in spring beans. @Qualifier – with @Autowired annotation to avoid confusion when multiple instances of bean type is present. @Service – for service classes. @Scope – for configuring the scope of the spring bean. @Configuration, @ComponentScan and @Bean – for java based configuration

Answer 63

Object-relational mapping or ORM is the programming technique to map application domain model objects to the relational database tables. Hibernate is Java-based ORM tool that provides a framework for mapping application domain objects to the relational database tables and vice versa. Hibernate provides a reference implementation of Java Persistence API, that makes it a great choice as ORM tool with benefits of loose coupling. We can use the Hibernate persistence API for CRUD operations. Hibernate framework provide option to map plain old java objects to traditional database tables with the use of JPA annotations as well as XML based configuration.

Answer 64

Hibernate has a layered architecture which helps the user to operate without having to know the underlying APIs. Hibernate makes use of the database and configuration data to provide persistence services (and persistent objects) to the application. It includes many objects such as persistent object, session factory, transaction factory, connection factory, session, transaction etc.

Answer 65

Implementation ArrayList: Implements List interface. HashSet: Implements Set interface. Duplicates ArrayList: Allows duplicates values. HashSet: Doesn’t allow duplicates values. Constructor ArrayList: Have three constructor which are ArrayList (), ArrayList (int capacity), ArrayList (int Collection c). HashSet: Have four constructor which are HashSet (), HashSet (int capacity), HashSet (Collection c), and HashSet (int capacity, float loadFactor). Order ArrayList: Maintains the order of the object in which they are inserted. HashSet: Doesn’t maintain any order. Null Object ArrayList: It’s possible to add any number of null value. HashSet: Allow one null value.

Answer 66

For those who don't know Java is both the compiler and interpreter language. When you compile a Java program creates a .class file which is a collection of byte code, these byte codes are not machine instructions instead they are instructions which Java a virtual machine can understand. Since every Java program runs on Java virtual machine, the same byte code can be run on any platform. the key is byte code is not machine instruction they are platform-independent instruction to JVM. On another hand, JVM or Java virtual machine is platform-dependent because it converts byte code into machine level instruction which is platform-specific and that's why you have a different version of JDK and JRE for windows and Linux because both JDK and JRE come with Java virtual machines. if you are confused between JVM, JRE and JDK then read my post on the difference between JDK, JRE, and JVM in Java.

Answer 67

Byte code is created when you compile Java program using Java compiler "javac" and byte code runs on JVM which is created by running the "java" command. In detail when you run "java" command it creates Java virtual machine, loads Main class specified in the command line and calls the standard main method in java. In summary combination of bytecode and JVM makes the Java program platform-independent. Write once run everywhere was Java’s mantra when it started ruling the programming world in the mid and late ’90s. Always remember, Java programs are platform independent but JVM is not. That's why you have different JVM and JRE installations for different platforms like Mac, Windows, Linux, or Solaris. Similarly, there are different JVM for 32-bit and 64-bit machines. Java has always been famous for its platform independent and write once run everywhere (WORA) feature and that's why it is still popular after 25 years of its creation. There are many more programming language and platform created after Java which uses same feature like .NET CLR (Common Language Runtime) which also offer platform independency for .NET application.

Answer 68

ClassLoader in Java is a class that is used to load class files in Java. Java code is compiled into a class file by javac compiler and JVM executes the Java program, by executing byte codes written in the class file. ClassLoader is responsible for loading class files from file systems, networks, or any other source. There is three default class loader used in Java, Bootstrap, Extension, and System or Application class loader. In short here is the location from which Bootstrap, Extension, and Application ClassLoader load Class files. 1) Bootstrap ClassLoader - JRE/lib/rt.jar 2) Extension ClassLoader - JRE/lib/ext or any directory denoted by java.ext.dirs 3) Application ClassLoader - CLASSPATH environment variable, -classpath or -cp option, Class-Path attribute of Manifest inside JAR file.

Answer 69

Autoboxing and unboxing are introduced in Java 1.5 to automatically convert the primitive type into boxed primitive( Object or Wrapper class). autoboxing allows you to use primitive and object types interchangeably in Java in many places like an assignment, method invocation, etc. If you have been using Collections like HashMap or ArrayList before Java 1.5 then you are familiar with the issues like you can not directly put primitives into Collections, instead, you first need to convert them into Object only then only you can put them into Collections. Wrapper classes like Integer, Double and Boolean help for converting primitive to Object but that clutter the code. With the introduction of autoboxing and unboxing in Java, this primitive to object conversion happens automatically by the Java compiler which makes the code more readable.

Answer 70

Overriding happens at subclass while Overloading happens in the same class. Also, overriding is a runtime activity while overloading is resolved at compile time.

Answer 71

StringBuilder is not synchronized while StringBuffer is synchronized. One of the most notable differences between StringBuilder, StringBuffer, and String in Java is that both StringBuffer and StringBuilder are Mutable classes but String is Immutable in Java. What this means is, you can add, remove or replace characters from StringBuffer and StringBuilder object but any change on the String object like converting uppercase to lowercase or appending a new character using String concatenation will always result in a new String object Another key difference between them is that both StringBuffer and String are thread-safe but StringBuilder is not thread-safe in Java. String achieves its thread-safety from Immutability but StringBuffer achieves it via synchronization, which is also the main difference between the StringBuffer and StringBuilder in Java.