Q1. What is the difference between an Inner Class and a Sub-Class? Ans: An Inner class is a class which is nested within another class. In this guide we will discuss about different types of questions that can be used in a Java interview, in order for the employer to test your skills in Java and. Moreover, many interview questions have different solutions. This book popular programming languages (C, C++, C#, and Java) are discussed in Chapter 2.
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Java Interview Questions And Answers Pdf Yes, We can execute any code, even before the main method. We are using a static block. Coding is an integral part of any programming job interviews Java development interviews are no exception. I would even suggest you should. In this section, we are giving few java interview programs faced by some of my friends. If you come across any questions, post it to me. I can provide solutions.
A sub-class is a class which inherits from another class called super class. Sub-class can access all public and protected methods and fields of its super class. What are the various access specifiers for Java classes? Ans: In Java, access specifiers are the keywords used before a class name which defines the access scope. The types of access specifiers for classes are: 1. Public : Class,Method,Field is accessible from anywhere.
Protected:Method,Field can be accessed from the same class to which they belong or from the sub-classes,and from the class of same package,but not from outside. Default: Method,Field,class can be accessed only from the same package and not from outside of it's native package. Private: Method,Field can be accessed from the same class to which they belong.
What's the purpose of Static methods and static variables?
Ans: When there is a requirement to share a method or a variable between multiple objects of a class instead of creating separate copies for each object, we use static keyword to make a method or variable shared for all objects. What is data encapsulation and what's its significance? Ans: Encapsulation is a concept in Object Oriented Programming for combining properties and methods in a single unit. Encapsulation helps programmers to follow a modular approach for software development as each object has its own set of methods and variables and serves its functions independent of other objects.
Encapsulation also serves data hiding purpose. What is a singleton class? Give a practical example of its usage.
A singleton class in java can have only one instance and hence all its methods and variables belong to just one instance. Singleton class concept is useful for the situations when there is a need to limit the number of objects for a class. The best example of singleton usage scenario is when there is a limit of having only one connection to a database due to some driver limitations or because of any licensing issues.
What are Loops in Java? What are three types of loops?
Java Interview Questions and Answers PDF eBook Free Download (250+ Questions, 60 Pages)
Ans: Looping is used in programming to execute a statement or a block of statement repeatedly. There are three types of loops in Java: 1 For Loops For loops are used in java to execute statements repeatedly for a given number of times. For loops are used when number of times to execute the statements is known to programmer. In while loops, condition is checked first before execution of statements. Hence in case of do while loop, statements are executed at least once.
Q7: What is an infinite Loop? How infinite loop is declared? Ans: An infinite loop runs without any condition and runs infinitely. An infinite loop can be broken by defining any breaking logic in the body of the statement blocks. What is the difference between continue and break statement? Ans: break and continue are two important keywords used in Loops.
When a break keyword is used in a loop, loop is broken instantly while when continue keyword is used, current iteration is broken and loop continues with next iteration. In below example, Loop is broken when counter reaches 4. What is the difference between double and float variables in Java? Ans: In java, float takes 4 bytes in memory while Double takes 8 bytes in memory. Float is single precision floating point decimal number while Double is double precision decimal number. What is Final Keyword in Java?
Give an example. Ans: In java, a constant is declared using the keyword Final. Value can be assigned only once and after assignment, value of a constant can't be changed.
This method are faster than any other method,because they are resolved at complied time. When a class is declares as final,it cannot be subclassed. Example String,Integer and other wrapper classes. What is ternary operator? Ans: Ternary operator , also called conditional operator is used to decide which value to assign to a variable based on a Boolean value evaluation.
It's denoted as? In the below example, if rank is 1, status is assigned a value of "Done" else "Pending". Ans: Using Math. What is default switch case? Give example.
Ans: In a switch statement, default case is executed when no other switch condition matches. Default case is an optional case. It can be declared only once all other switch cases have been coded. In the below example, when score is not 1 or 2, default case is used. What's the base class in Java from which all classes are derived? Ans: java. Can main method in Java can return any data?
Ans: In java, main method can't return any data and hence, it's always declared with a void return type. What are Java Packages? What's the significance of packages? Ans: In Java, package is a collection of classes and interfaces which are bundled together as they are related to each other.
Use of packages helps developers to modularize the code and group the code for proper re-use. Once code has been packaged in Packages, it can be imported in other classes and used. Can we declare a class as Abstract without having any abstract method? Ans: Yes we can create an abstract class by using abstract keyword before class name even if it doesn't have any abstract method. However, if a class has even one abstract method, it must be declared as abstract otherwise it will give an error.
What's the difference between an Abstract Class and Interface in Java? Ans: The primary difference between an abstract class and interface is that an interface can only possess declaration of public static methods with no concrete implementation while an abstract class can have members with any access specifiers public, private etc with or without concrete implementation.
Another key difference in the use of abstract classes and interfaces is that a class which implements an interface must implement all the methods of the interface while a class which inherits from an abstract class doesn't require implementation of all the methods of its super class. A class can implement multiple interfaces but it can extend only one abstract class. What are the performance implications of Interfaces over abstract classes? Ans: Interfaces are slower in performance as compared to abstract classes as extra indirections are required for interfaces.
Another key factor for developers to take into consideration is that any class can extend only one abstract class while a class can implement many interfaces. Use of interfaces also puts an extra burden on the developers as any time an interface is implemented in a class; developer is forced to implement each and every method of interface.
Does Importing a package imports its sub-packages as well in Java? Ans: In java, when a package is imported, its sub-packages aren't imported and developer needs to import them separately if required.
For example, if a developer imports a package university. To load the classes from its sub-package say department , developer has to import it explicitly as follows: Import university. Can we declare the main method of our class as private? Ans: In java, main method must be public static in order to run any application correctly. If main method is declared as private, developer won't get any compilation error however, it will not get executed and will give a runtime error.
How can we pass argument to a function by reference instead of pass by value?
Top 100 Java Interview Questions with Answers
Ans: In java, we can pass argument to a function only by value and not by reference. How an object is serialized in java? Ans: In java, to convert an object into byte stream by serialization, an interface with the name Serializable is implemented by the class. All objects of a class implementing serializable interface get serialized and their state is saved in byte stream.
When we should use serialization? Ans: Serialization is used when data needs to be transmitted over the network. Using serialization, object's state is saved and converted into byte stream. The byte stream is transferred over the network and the object is re-created at destination.
Ans: Try block needs to be followed by either Catch block or Finally block or both.
You need to write code in such a way that no deadlock should occur. The trick to solving this problem is acquiring resources in an order and release them in reverse order e. This way you can avoid deadlock. Factorial solution This is one of the simplest programs you can expect on interviews.
It is generally asked to see if you can code or not. Sometimes interviewer may also ask about changing a recursive solution to iterative one or vice-versa.
Reverse a String solution This problem is similar to the String Palindrome problem we have discussed above. If you can solve that problem you can solve this as well. You can use indexOf or substring to reverse a String or alternatively, convert the problem to reverse an array by operating on character array instead of String.
Remove duplicates from array solution Write a program to remove duplicates from an array in Java without using the Java Collection API.
The array can be an array of String, Integer or Character, your solution should be independent of the type of array. If you want to practice more array based questions then see this list of top 30 array interview questions from Java interviews.
Printing patterns solutions Print repeated characters of String? GCD of two numbers solution Square root of number solution You need to write a program to calculate the square root of a number without using the Math.
You need to write your logic and method to calculate the square root. You can though use popular algorithm e. Newton's method. Reverse array in place solution Reverse words of sentence solution Leap year solution Binary search solution String Anagram solution Write a program to check if two given String is Anagram of each other.
Your function should return true if two Strings are Anagram, false otherwise. A string is said to be an anagram if it contains same characters and same length but in different order e. You can ignore cases for this problem but you should clarify that from your interview. You will be given 3 hours to design and code a vending machine satisfying some of the business requirements. You also need to write unit tests to prove your code satisfy those requirements.
You can see this article for more object oriented analysis questions. Reverse a number solution The first non-repeated character of String solution Finding Middle element of linked list in one pass solution Pre-order traversal solution Pre-order traversal without recursion solution In order traversal solution In order traversal without recursion solution Post-order traversal solution Post order traversal without recursion solution Print all leaves of binary tree solution Sort array using quicksort solution You need to write a Java program to sort an array of integers using quick sort algorithm.
You cannot use any library method e. JDK or a third party library, which means, you need to first implement the quicksort algorithm and then sort the array. Insertion sort solution Write a program to implement the insertion sort algorithm in Java. The program should take an unsorted array and sort it using insertion sort algorithm Also explain the best case and worst case time and space complexity of Insertion sort algorithm.
Bubble sort solution Write a program to implement the bubble sort algorithm in Java. You can use basic operators and functions but sorting functions from Java API is not allowed. Transpose a matrix solution Print all permutations of String solution Write a Java program to print all permutations of a given String. For example, if given String is "GOD" then your program should print all 6 permutations of this string e.
Share to Twitter Share to Facebook. Coding Interview Question , core java interview question , Programming interview question. Anonymous said Nice collection of interview question October 12, at 2: Good Programmas December 11, at Good collection February 11, at 9: Do you know any other books recommended for coding interviews?
July 13, at 2: Thank you. March 23, at 1: Newer Post Older Post Home.
Subscribe to: Post Comments Atom. Follow by Email.What is ternary operator? How can you generate random numbers in Java?
Java Exception Handling Interview questions. Encapsulation helps programmers to follow a modular approach for software development as each object has its own set of methods and variables and serves its functions independent of other objects.
If we want to use such collections where we may require a change of size no of items , we should prefer vector over array. Memory isn't allocated before creation of objects.
Objects are the instances of classes which interacts with one another to design applications and programs. In java, a thread which is in dead state can't be started again.
Answer: Finally block will not be executed whenever jvm shutdowns.
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