Software Engineer

AJAX communicates with the server using XMLHttpRequest object. XMLHttpRequest object plays a important role.
User sends a request from the UI and a javascript call goes to XMLHttpRequest object.
HTTP Request is sent to the server by XMLHttpRequest object.
Server interacts with the database using JSP, PHP, Servlet, ASP.net etc.
Data is retrieved.
Server sends XML data or JSON data to the XMLHttpRequest callback function.
HTML and CSS data is displayed on the browser.

SOAP stands for Simple Object Access Protocol whereas REST stands for Representational State Transfer.
SOAP is a protocol whereas REST is an architectural pattern.
SOAP uses service interfaces to expose its functionality to client applications while REST uses Uniform Service locators to access to the components on the hardware device.
SOAP needs more bandwidth for its usage whereas REST doesn’t need much bandwidth.
Comparing SOAP vs REST API, SOAP only works with XML formats whereas REST work with plain text, XML, HTML and JSON.
SOAP cannot make use of REST whereas REST can make use of SOAP.

1) In case of Get request, only limited amount of data can be sent because data is sent in header. In case of post request, large amount of data can be sent because data is sent in body.
2) Get request is not secured because data is exposed in URL bar. Post request is secured because data is not exposed in URL bar.
3) Get request can be bookmarked. Post request cannot be bookmarked.
4) Get request is idempotent . It means second request will be ignored until response of first request is delivered Post request is non-idempotent.
5) Get request is more efficient and used more than Post. Post request is less efficient and used less than get.

Observer pattern is used when there is one-to-many relationship between objects such as if one object is modified, its depenedent objects are to be notified automatically. Observer pattern falls under behavioral pattern category.
Implementation : Observer pattern uses three actor classes. Subject, Observer and Client. Subject is an object having methods to attach and detach observers to a client object.

In object-oriented programming, a singleton class is a class that can have only one object (an instance of the class) at a time. After the first time, if we try to instantiate the Singleton class, the new variable also points to the first instance created. So whatever modifications we do to any variable inside the class through any instance, affects the variable of the single instance created and is visible if we access that variable through any variable of that class type defined.

An object is considered immutable if its state cannot change after it is constructed. Maximum reliance on immutable objects is widely accepted as a sound strategy for creating simple, reliable code.
Immutable objects are particularly useful in concurrent applications. Since they cannot change state, they cannot be corrupted by thread interference or observed in an inconsistent state.

Dependency injection is basically providing the objects that an object needs (its dependencies) instead of having it construct them itself. It's a very useful technique for testing, since it allows dependencies to be mocked or stubbed out.
Dependencies can be injected into objects by many means (such as constructor injection or setter injection). One can even use specialized dependency injection frameworks (e.g. Spring) to do that, but they certainly aren't required. You don't need those frameworks to have dependency injection. Instantiating and passing objects (dependencies) explicitly is just as good an injection as injection by framework.

To create an immutable class in Java, you have to do the following steps.
1) Declare the class as final so it can’t be extended.
 

2) Make all fields private so that direct access is not allowed.
 

3) Don’t provide setter methods for variables.
 

4) Make all mutable fields final so that its value can be assigned only once.
 

5) Initialize all the fields via a constructor performing deep copy.
 

6) Perform cloning of objects in the getter methods to return a copy rather than returning the actual object reference.

Tip 1 : The cross questioning can go intense some time, think before you speak.

Tip 2 : Be open minded and answer whatever you are thinking, in these rounds I feel it is important to have opinion.

Tip 3 : Context of questions can be switched, pay attention to the details. It is okay to ask questions in these round, like what are the projects currently the company is investing, which team you are mentoring. How all is the work environment etc.