Java Full Stack Interview Questions – 3 Yrs

1. What are wrapper classes in Java?

A class containing primitive data types. When we are creating an object to a wrapper class, a field is available to store primitive data types.

2. What is the difference between an Array list and a vector in Java?

Vector and ArrayList uses arrays as data structures internally. They are dynamically resizable. But, ArrayList increases by half of its size when its size is increased. Therefore as per Java API the only main difference is, Vector’s methods are synchronized and ArrayList’s methods are not synchronized.

3. How does cookies work in Servlets?

In cookies technique, we add cookies with response from the servlet. So the cookie is stored in the cache of the browser. After that if a request is sent by the user, a cookie is added with the request by default. Thus, we recognize the user as the old user.

4. Can we declare a class as Abstract without having any abstract method?

Yes, we can declare an abstract class without any abstract method. The purpose of declaring a class as abstract is not to instantiate the class. Declaring an abstract class means that it cannot be instantiated on its own and can only be subclassed.

5. Why is the Runnable Interface used in Java?

The Runnable interface should be implemented by any class whose instances are intended to be executed by a thread. The class must define a method of no arguments called run. It is designed to provide a common protocol for objects that wish to execute code while they are active.

6. How to design a Good Key for HashMap?

Designing a good key results in efficient and predictable hashing behavior. The Key points to be considered are:

Keys should have constant hash code
Good distribution of hash code
equals() has to be consistent with hashCode()
Implement the Comparable interface to sort and order keys.

7. What are memory areas allocated in JVM?

The Java virtual machine memory is a runtime area used for the execution of various programs. The memory area of a JVM is broadly divided into different parts, such as:

Method area,
Heap area,
Stack,
Program counter (PC) registers area,
Native method area.

8. Can you explain the internal workings of HashSet in java?

HashSet uses HashMap internally to store its objects. Whenever you create a HashSet object, one HashMap object associated with it is also created. This HashMap object is used to store the elements you enter in the HashSet. The elements you add into HashSet are stored as keys of this HashMap object.

9. Difference between controlled and uncontrolled components?

In a controlled component, form data is handled by a React component which allows validation control. In uncontrolled components, form data is handled by the DOM itself and uses a ref to get form values from DOM.

10. “In React, everything is a component.” Explain?

Components are the building blocks of a React application’s UI which splits up the entire UI into small independent.

11. What is Shallow Rendering in React testing?

Shallow rendering is a valuable technique for unit testing. It provides a controlled environment to render a component without rendering its child components. It is useful to ensure that the component works correctly, regardless of its children.

12. What is ReactDOMServer?

The ReactDOMServer object enables rendering components to static markup which is mainly used for server-side rendering (SSR). The following methods can be used in both the server and browser environments:

renderToString()
renderToStaticMarkup()

13. What are the Pointer Events supported in React?

Pointer Events provide a unified way of handling all input events. Many devices are used nowadays that don’t correlate with a mouse, like phones with touch surfaces or pens. So we need to remember that these events will only work in browsers that support the Pointer Events specification.

14. How to format date using React Intl?

The injectIntl() higher-order component will give access to the formatDate() method via the props in the component. It is used internally by instances of FormattedDate and it returns the string representation of the formatted date.

15. What is the difference between $scope and scope in Angular?

In Angular js $scope is used whenever we have to use dependency injection (D.I) whereas the scope is used for directive linking.

16. How did you get the value from the input box using JQuery?

To get the textbox value, use the jQuery val() function. For example, $(‘input:textbox’). val() – Get textbox value.

17. Explain about let and const in ES6

In ES6 “const” will have block scoping just like the “let” keyword. A constant is a block scope that cannot be shared its name with a function or a variable in the same scope. The value of a constant cannot change through re-assignment. The const declaration creates a read-only reference to a value.

18. What is TypeScript?

TypeScript is a free, open source programming language which is developed by Microsoft. TypeScript is a syntactical superset of JavaScript. It is easy to maintain and comfortable to interpret.

19. What is @NgModule?

An NgModule is a class marked by the @NgModule decorator. @NgModule is a decorator for building web applications. The key features of @NgModule are:

Imports
Declarations
Providers
Exports
Bootstrap

20. What is the Traceur compiler?

Traceur compiler takes classes, generators, and other features from ECMAScript edition 6 (ES6) and compiles it into JavaScript ES5 that runs on the browser. This means developers can use the code from a future version that has more features and encourages design patterns.

21. What is NaN property in JavaScript?

NaN stands for Not a Number which represents a value that is not a valid number. It can be used to check whether a number entered is a valid number or not a number. To assign a variable to NaN value, we can use one of the two following ways.

var a = NaN var a = Number.NaN.

22. Explain Higher Order Functions in JavaScript?

Functions can be assigned to variables in the same way that strings or arrays can. They can be passed into other functions as parameters or returned from them as well. A “higher-order function” is a function that accepts functions as parameters and/or returns a function.

23. What are the rules to be followed for variable naming conventions in JavaScript?

Rules:

JavaScript variable names are case sensitive. For example, Test and test are two different variables.
Don’t use any of the JavaScript reserved keywords as variable names. For example, break or boolean variable names are not valid.
JavaScript variable names should not start with a numeral (0-9). They must begin with a letter or the underscore character. For example, 123name is an invalid variable name but _123name or name123 is a valid one.

24.What are all the loops available in JavaScript?

JavaScript provides several types of loops to handle repeated tasks, such as:

For loop
While loop
do.. while loop
For…in loop
For…of loop

25. What are the different types of errors available in JavaScript?

The three types of errors are:

Load time Errors: come up when we load a web page with inappropriate syntax Errors. They are generated dynamically.
Run time Errors: are generated due to misuse of command inside an HTML language.
Logical Errors: occur due to the formation or writing off bad logic inside the program.

26. Write a Java program to find the first non-repeated character in a string.

import java.util.LinkedHashMap; import java.util.Map; public class FirstNonRepeatedCharacter { public static char firstNonRepeatedChar(String str) { Map<Character, Integer> charCountMap = new LinkedHashMap<>(); for (char c : str.toCharArray()) { charCountMap.put(c, charCountMap.getOrDefault(c, 0) + 1); } for (Map.Entry<Character, Integer> entry : charCountMap.entrySet()) { if (entry.getValue() == 1) { return entry.getKey(); } } throw new RuntimeException(No non-repeated character found); } public static void main(String[] args) { String str =swiss; System.out.println(First non-repeated character: + firstNonRepeatedChar(str)); } }

27. What is the difference between an abstract class and an interface in Java?

Abstract class:

Can have both abstract and non-abstract methods.
Can have constructors and member variables.
Supports multiple levels of abstraction (i.e., it can implement other interfaces and extend another abstract class).
A class can only extend one abstract class due to single inheritance.
Use an abstract class when you want to share code among several closely related classes.

Interface:

Only abstract methods by default (but can also have default and static methods in Java 8+).
Cannot have instance variables or constructors.
Supports multiple inheritance, meaning a class can implement multiple interfaces.
Use an interface when you want to define a contract that unrelated classes can implement.

28. How would you reverse the words in a string while preserving the word order in Java?

Reversing the words in a string while preserving the order means reversing each word individually but keeping the sequence of the words intact.

public class ReverseWords { public static String reverseWords(String input) { String[] words = input.split(” “); StringBuilder result = new StringBuilder(); for (String word : words) { StringBuilder reversedWord = new StringBuilder(word).reverse(); result.append(reversedWord).append(” “); } return result.toString().trim(); // Remove the trailing space } public static void main(String[] args) { String input = “Hello World”; System.out.println(reverseWords(input)); } }

29. What is runtime polymorphism? Is it called Dynamic method dispatch?

Runtime polymorphism is a process to resolve a call to an overridden method at runtime time. It is performed using virtual functions. The concept of Runtime polymorphism is also called dynamic method dispatch.

30. What is a package in Java? List down various advantages of packages.

Java package is used to categorize the classes and interfaces so that they can be easily maintained. The advantages of packages are:

Grouping of related classes and interfaces makes them more modular and easier to manage. Packages help in avoiding name conflicts.
Enhance reusability across multiple applications in different projects. To encapsulate the implementation details of classes.
Allows implementation of access control mechanisms that enhance security. Simplifies the maintenance and updation of the relevant code.

31. What is multiple inheritance? Is it supported by Java?

Multiple Inheritance is a feature of object oriented concepts. It allows a class to inherit properties of more than one parent class. Java doesn’t support multiple inheritance of classes.

32. Why Java does not support pointers?
Pointer is a variable that refers to the memory address. They are not used in java because they are unsafe(unsecured) and complex to understand.

33. Write about loose coupling and tight coupling

Loose coupling: occurs when classes are designed to be independent of one another. They interact through well-defined interfaces or abstract classes.

Tight coupling: occurs when classes are highly dependent on each other. One class directly instantiates or tightly integrates with another.

34. What is synchronized collection in Java?

Synchronized collections are responsible for thread-safety. These collections internally handle synchronization. It ensures that only one thread can access a method at a time. Synchronized collections prevent concurrent modification issues and data corruption.

35. How events are handled differently in React JS?

Event handling is efficient in React JS using different ways, such as:

Synthetic Events by wrapping native browser events in a cross-browser wrapper called SyntheticEvent.
Event handlers are defined in the component using camelCase syntax. Event Delegation is achieved by attaching a single event listener to the root of the document.
Event handlers interact with the component’s state using hooks like useState and useEffect. Event handler methods need to be bound to the component instance explicitly.

36. What are React Mixins?

Mixins extend the class they are mixed into, while HOCs compose classes and return new classes. Mixins can set State in components since they are going to be part of that component. HOCs should not set State since they are only functions that take a class and return another class, they communicate through props instead.

37. What are the controlled components and uncontrolled components in ReactJS?

Controlled component is component which gets the changed value from the callback function and uncontrolled component is component that has the one from the DOM. For example, when input value is changed, we can use onChange function in Controlled Component and also we can get the value using DOM like ref.

38. What are stateless components in ReactJS?

Stateless components are those components which don’t have any state at all, which means you can’t use this. setState inside these components. It is like a normal function with no render method. It has no lifecycle, so it is not possible to use lifecycle methods such as componentDidMount and other hooks.

39. Event binding angular

Event binding is used to handle the events raised by the user actions like button click, mouse movement, keystrokes, etc. When the DOM event happens at an element(e.g. click, keydown, keyup), it calls the specified method in the particular component.

40. Difference between promise and observables

Promises deal with one asynchronous event at a time, while observables handle a sequence of asynchronous events over a period of time.

41. What does Angular Material mean?

Angular Material is a User Interface component library. It is used to speed up the development of the user interfaces. Angular Material offers reusable and beautiful UI components.It allows to develop fully functional web pages,and applications.

42. What Is Deep Linking In AngularJs?

Deep linking is a usage of the URL which will take the specific page Content without traversing the application home page. It helps for the indexed so that this link can be easily searchable by the SEO like google yahoo, etc.

43. How To Implement Internationalization In AngularJs?

The two approaches to providing locale rules to AngularJS:

Pre-bundled rule sets with AngularJS by concatenating the content of the locale-specific file to the end of angular. js or angular.
Including a locale script in index. html.

44. Explain Implicit Type Coercion in JavaScript?

Type Coercion refers to the process of automatic or implicit conversion of values from one data type to another. This includes conversion from Number to String, String to Number, Boolean to Number etc. when different types of operators are applied to the values.

45. What are undeclared and undefined variables?

Undefined: It occurs when a variable has been declared but has not been assigned with any value. Undefined is not a keyword. Undeclared: It occurs when we try to access any variable that is not initialized or declared earlier using var or const keyword.

46. What is Currying?

Currying is an advanced technique of working with functions. It’s used not only in JavaScript, but in other languages as well. It is a transformation of functions that translates a function from callable as f(a, b, c) into callable as f(a)(b)(c) . Currying doesn’t call a function. It just transforms it.

47. How to create an array in JavaScript?

Create an array in JavaScript

By array literal
By creating an instance of Array
By using an Array constructor

48. What are Pseudo classes?

Pseudo-classes are the type of pseudo-elements that don’t exist in a normal document tree. It allows selecting the regular elements under certain conditions especially when we try to hover over the link; the anchor tags are :link, :visited, :hover, :active, :focus

In this example, the color will be red on the anchor tag when it’s hovered.

/* mouse over link */ a:hover { color: #FFOOFF; }

49. What Is Ecmascript?

JavaScript is formally known as ECMAScript also known as “ES6” which is the new version of JavaScript offers a number of new features that extend the power of the language. Angular makes use of a number of features of ES6 and TypeScript.

50. What are the differences between adaptive design and responsive design?

Adaptive Design:

Main focus is to develop a website in multiple fixed layout sizes.
It is very time-consuming and takes a lot of effort to build the best possible adaptive design as examining it will need to go for many options with respect to the realities of the end user.
There are six standard screen sizes for the appropriate layouts; they are 320px, 480px, 760px, 960px, 1200px, 1600px to design.
Responsive Design
Main focus is to show content with respect to browser space.
Offers less control over the design.
It takes less time to build the design and there is no screen size issue irrespective of content.
It uses CSS media queries to design the screen layouts with respect to specific devices and property changes in the screen.

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Java Full Stack Interview Questions – 3 Yrs