Integration Programmer

Mock object are very useful to test an individual unit in your Software, in fact stud and mocks are powerful tool for creating automated unit tests. Suppose you write a program to display currency conversion rates but you don't have a URL to connect to, now if you want to test your code, you can use mock objects. In Java world, there are lot of frameworks which can create powerful mock objects for you e.g. Mockito and PowerMock.

A class is said to be Immutable if its state cannot be changed once created, for example String in Java is immutable. Once you create a String say "Java", you cannot change its content. Any modification in this string e.g. converting into upper case, concatenating with another String will result in new object. Immutable object are very useful on concurrent programming because they can be shared between multiple threads without worrying about synchronization. In fact, whole model of functional programming is built on top of Immutable objects.

A class is a blue print on which objects are created. A class has code and behavior but an object has state and behavior. You cannot create an object without creating a class to represent its structure. Class is also used to map an object in memory, in Java, JVM does that for you.

V stands for View in MVC pattern. View is what user sees e.g. web pages. This is a very important design pattern of web development which is based upon segregation of concern, so that each area can be modified without impacting other areas. In Java world, there are lots of open source framework which provides implementation of MVC pattern e.g. Struts 2 and Spring MVC. By the way, M stands for model and C stands for controller. Modes are actual business objects e.g. User, Employee, Order while controller is used to route request to correct processor.

Loose coupling is a desirable quality of software, which allows one part of software to modify without affecting other part of software. For example in a loosely coupled software a change in UI layout should not affect the back-end class structure.

This is the most classical question of all programming interviews. An interface is the purest form of abstraction with nothing concrete in place, while an abstract class is a combination of some abstraction and concrete things. The difference may vary depending upon language e.g. in Java you can extend multiple interface but you can only extend on abstract class. For a more comprehensive discussion see the detailed answer.

Association means two objects are related to each other but can exists without each other, Composition is a form of association where one object is composed of multiple object, but they only exists together e.g. human body is composition of organs, individual organs cannot live they only useful in body. Aggregation is collection of object e.g. city is aggregation of citizens.

DOM parser is a in memory parser so it loads whole XML file in memory and create a DOM tree to parse. SAX parser is a event based parser, so it parses XML document based upon event received e.g. opening tag, closing tag, start of attribute or end of attribute. Because of their working methodology, DOM parser is not suitable for large XML file as they will take lot of space in memory and your process may ran out of memory, SAX is the one which should be used to parse large files. For small files, DOM is usually much faster than SAX.

In a strongly typed language compiler ensure type correctness, for example you can not store number in String or vice-versa. Java is a strongly typed language, that's why you have different data types e.g. int, float, String, char, boolean etc. You can only store compatible values in respective types. On the other hand, weakly typed language don't enforce type checking at compile time and they tree values based upon context. Python and Perl are two popular example of weakly typed programming language, where you can store a numeric string in number type.

SQL injection is a security vulnerability which allows intruder to steal data from system. Any system which take input from user and create SQL query without validating or sanitizing that input is vulnerable to SQL injection. In such system, intruder can inject SQL code instead of data to retrieve more than expected data. There are many instances on which sensitive information e.g. user id, password and personal details are stolen by exploiting this vulnerability. In Java, you can avoid SQL injection by using Prepared statement.

A process can have multiple threads but a thread always belongs to a single process. Two process cannot share memory space until they are purposefully doing inter process communication via shared memory but two threads from same process always share same memory.

A well-formed XML is the one which has root element and all tags are closed properly, attributes are defined properly, their value is also quoted properly. On other hand, a valid XML is the one which can be validated against a XSD file or schema. So it's possible for a XML to be well-formed but not valid, because they contain tags which may not be allowed by their schema.

In SQL, there are mainly two types of joins, inner join and outer join. Again outer joins can be two types right and left outer join. Main difference between inner join and left join is that in case of former only matching records from both tables are selected while in case of left join, all records from left table is selected in addition to matching records from both tables. Always watch out for queries which has "all" in it, they usually require left join e.g. write sql query to find all departments and number of employees on it. If you use inner join to solve this query, you will missed empty departments where no one works.

Unit testing, integration testing and smoke testing. Unit testing is used to test individual units to verify whether they are working as expected, integration testing is done to verify whether individually tested module can work together or not and smoke testing is a way to test whether most common functionality of software is working properly or not e.g. in a flight booking website, you should be able to book, cancel or change flights.

Iteration uses loop to perform same step again and again while recursion calls function itself to do the repetitive task. Many times recursion result in a clear and concise solution of complex problem e.g. tower of Hanoi, reversing a linked list or reversing a String itself. One drawback of recursion is depth, since recursion stores intermediate result in stack you can only go upto certain depth, after that your program will die with StackOverFlowError, this is why iteration is preferred over recursion in production code.

By using modulus operator, number % 10 returns the last digit of the number, for example 2345%10 will return 5 and 567%10 will return 7. Similarly division operator can be used to get rid of last digit of a number e.g. 2345/10 will give 234 and 567/10 will return 56. This is an important technique to know and useful to solve problems like number palindrome or reversing numbers.

Answer is zero, because XOR returns 1 if two operands are distinct and zero if two operands are same, for example 0 XOR 0 is also zero, but 0 XOR 1 or 1 XOR 0 is always 1.

Test driven is one of the popular development methodology in which tests are written before writing any function code. In fact, test drives the structure of your program. Purists never wrote a single line of application code without writing test for that. It greatly improve code quality and often attributed as a quality of rockstar developers.

Liskov substitution principle is one of the five principle introduced by Uncle Bob as SOLID design principles. It's the 'L' in SOLID. Liskov substitution principle asserts that every sub type should be able to work as proxy for parent type. For example, if a method except object of Parent class then it should work as expected if you pass an object of Child class. Any class which cannot stand in place of its parent violate LSP or Liskov substitution principle. This is actually a tough question to answer and if you does that you end up with creating a good impression on interviewers mind.

Open closed is another principle from SOLID, which asserts that a system should be open for extension but close for modification. Which means if a new functionality is required in a stable system then your tried and tested code should not be touched and new functionality should be provided by adding new classes only.