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Q1861. How does a try statement determine which catch clause should be used to handle an exception?

Ans. When an exception is thrown within the body of a try statement, the catch clauses of the try statement are examined in the order in which they appear. The first catch clause that is capable of handling the exception is executed. The remaining catch clauses are ignored.

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Q1862. Describe what happens when an object is created in Java ?

Core Java

Ans. 1. Memory is allocated from heap to hold all instance variables and implementation-specific data of the object and its superclasses. Implemenation-specific data includes pointers to class and method data.
2. The instance variables of the objects are initialized to their default values.
3. The constructor for the most derived class is invoked. The first thing a constructor does is call the constructor for its superclasses. This process continues until the constructor for java.lang.Object is called,as java.lang.Object is the base class for all objects in java.
4. Before the body of the constructor is executed, all instance variable initializers and initialization blocks are executed. Then the body of the constructor is executed. Thus, the constructor for the base class completes first and constructor for the most derived class completes last.

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Very frequently asked. Usually asked in different variants like Diff between StringBuffer , String Builder ; Difference between StringBuilder and String class; Choice between these classes etc.

Q1863. What is the difference between StringBuffer and String class ?

Core Java

Ans. A string buffer implements a mutable sequence of characters. A string buffer is like a String, but can be modified. At any point in time it contains some particular sequence of characters, but the length and content of the sequence can be changed through certain method calls.

The String class represents character strings. All string literals in Java programs, such as "abc" are constant and implemented as instances of this class; their values cannot be changed after they are created.

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Advanced level question usually asked in High end product companies. Have been asked in Google and Amazon (Based on 1 Feedback)

Q1864. Describe, in general, how java's garbage collector works ?

Core Java

Ans. The Java runtime environment deletes objects when it determines that they are no longer being used. This process is known as garbage collection. The Java runtime environment supports a garbage collector that periodically frees the memory used by objects that are no longer needed. The Java garbage collector is a mark-sweep garbage collector that scans Java dynamic memory areas for objects, marking those that are referenced. After all possible paths to objects are investigated, those objects that are not marked (i.e. are not referenced) are known to be garbage and are collected.

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Q1865. What is RMI ?

Ans. RMI stands for Remote Method Invocation. Traditional approaches to executing code on other machines across a network have been confusing as well as tedious and error-prone to implement. The nicest way to think about this problem is that some object happens to live on another machine, and that you can send a message to the remote object and get a result as if the object lived on your local machine. This simplification is exactly what Java Remote Method Invocation (RMI) allows you to do.

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Q1866. What is JDBC? Describe the steps needed to execute a SQL query using JDBC.

Database

Ans. The JDBC is a pure Java API used to execute SQL statements. It provides a set of classes and interfaces that can be used by developers to write database applications.

The steps needed to execute a SQL query using JDBC:

1. Open a connection to the database.
2. Execute a SQL statement.
3. Process th results.
4. Close the connection to the database.

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Q1867. Are constructors inherited? Can a subclass call the parent's class constructor? When?

Core Java

Ans. You cannot inherit a constructor. That is, you cannot create a instance of a subclass using a constructor of one of it's superclasses. One of the main reasons is because you probably don't want to override the superclasses constructor, which would be possible if they were inherited. By giving the developer the ability to override a superclasses constructor you would erode the encapsulation abilities of the language.

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Q1868. What is JSON ?

Json

Ans. JSON is "JavaScript Object Notation", primarily used for client-server or server-server communication. Its a much lighter and readable alternative to XML. JSON is language independent and is easily parse-able in all programming languages.

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Q1869. What is the role of JSON.stringify ?

Json

Ans. JSON.stringify() turns an object into a JSON text and stores that JSON text in a string.

So If we stringfy above notation , it will become

{"name":"xyz","gender":"male";"age":30}

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Q1870. Which data types are supported by JSON ?

Json

Ans. Number
String
Boolean
Array
Object
null

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Q1871. What are the benefits of JSON over XML ?

Json

Ans. Lighter and faster than XML as on-the-wire data format

Object Representation - Information is presented in object notations and hence better understandable.

Easy to parse and conversion to objects for information consumption.

Support multiple data types - JSON supports string, number, array, boolean whereas XML data are all string.

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Frequently asked. Favorite question in Walk in Drive of many Indian service companies.

Q1872. What are the methods of Object Class ?

Core Java

Ans. clone() - Creates and returns a copy of this object.

equals() - Indicates whether some other object is "equal to" this one.

finalize() - Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.

getClass() - Returns the runtime class of an object.

hashCode() - Returns a hash code value for the object.

toString() - Returns a string representation of the object.

notify(), notifyAll(), and wait() - Play a part in synchronizing the activities of independently running threads in a program.

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Q1873. Explain JMS ( Java Messaging Services ) ?

JMS

Ans. JMS Provides high-performance asynchronous messaging. It enables Java EE applications to communicate with non-Java systems on top of various transports.

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Q1874. Which MVC is struts2 based on ?

Ans. MVC2

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Q1875. What is an API ( Application Programming Interface ) ?

Ans. An API is a kind of technical contract which defines functionality that two parties must provide: a service provider (often called an implementation) and an application. an API simply defines services that a service provider (i.e., the implementation) makes available to applications.

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Q1876. What is URL?

Java EE

Ans. URL is Uniform Resource Locator which is representation of HTTP address.

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Q1877. Explain features of struts2 ?

Ans. 1) It is an Action based MVC based framework which has adopt mvc2.

2) Struts2 is a pull-MVC (or MVC2) framework where action takes the role of the model rather than the controller. The â€œpullâ€ concepts means views ability to pull data from an action, rather than having a separate model object available.

3) The Model View-Controller pattern in Struts2 is implemented with five core components â€“ actions, interceptors, value stack / OGNL, result types and results / view technologies.

4) XML configuration as well as Annotation option available.

5) POJO based action available so we can write test cases easily.

6) Integration with Spring, tiles and OGNL based expression langugae.

7) Theme based tag libraries integrated with struts tag as well as support of Ajax tag.

8) Can have various view options like jsp, velocity, freemarker etc.

9) We can embed plugin through which we can modify and extend framework features.

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Q1878. What is HTTP ?

Java EE

Ans. HTTP or Hypertext Transfer Protocol is internet protocol for tranmission of hypertext ( text with meta data ) over internet.

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Q1879. what is content negotiation?

Ans. Suppose we want to visit a site for any information, information can be represented in different languages like English,German or may be other and their format for presentation can also differ from HTML to PDF or may be Plain text. In this case when an client makes an HTTP request to a server, client can also specify the media types here. Client can specify what it can accept back from host and on the basis of availability the host will return to the client. This is called content negotiation because client and server negotiated on the language and format of the content to be shared.

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Q1880. Is tomcat an application or Web server ?

Server

Ans. Tomcat is a web server and a Servlet container. It is often used as an application server for web-based applications but does not include the complete suite of capabilities that a Java EE application server would supply.

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Q1881. What are the default or implicitly assigned values for data types in java ?

Ans. boolean ---> false
byte ----> 0
short ----> 0
int -----> 0
long ------> 0l
char -----> /u0000
float ------> 0.0f
double ----> 0.0d
any object reference ----> null

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Very frequently asked to Fresh graduates.

Q1882. What is the difference between Encapsulation and Abstraction?

Core Java

Ans. 1.Abstraction solves the problem at design level while encapsulation solves the problem at implementation level

2.Abstraction is used for hiding the unwanted data and giving relevant data. while Encapsulation means hiding the code and data into a single unit to protect the data from outside world.

3. Abstraction lets you focus on what the object does instead of how it does it while Encapsulation means hiding the internal details or mechanics of how an object does something.

4.For example: Outer Look of a Television, like it has a display screen and channel buttons to change channel it explains Abstraction but Inner Implementation detail of a Television how CRT and Display Screen are connect with each other using different circuits , it explains Encapsulation.

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Q1883. Can I import same package/class twice? Will the JVM load the package twice at runtime?

Core Java

Ans. One can import the same package or same class multiple times. Neither compiler nor JVM complains wil complain about it. And the JVM will internally load the class only once no matter how many times you import the same class.

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Q1884. Explain static blocks in Java ?

Core Java

Ans. A static initialization block is a normal block of code enclosed in braces, { }, and preceded by the static keyword. Here is an example:

static {
// whatever code is needed for initialization goes here
}

A class can have any number of static initialization blocks, and they can appear anywhere in the class body. The runtime system guarantees that static initialization blocks are called in the order that they appear in the source code.

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Q1885. Which access specifier can be used with Class ?

Core Java

Ans. For top level class we can only use "public" and "default". We can use private with inner class.

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Q1886. What is meant by an "asynchronous event." Give some examples ?

Operating System

Ans. An asynchronous event is one that occurs at an unpredictable time outside the control of the program that the CPU is running. It is not "synchronized" with the program.

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Q1887. Explain use of nested or inner classes ?

Core Java

Ans. Sometime we just need classes or class objects just to be used as part of a particular class or objects. Making them non nested won't make any difference as far as functionality is concerner but making them Nested provide a level of convenience and protection fro, being used anywhere else. Moreover it helps reducing the Code.

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Q1888. Explain Annotations ?

Ans. Annotations, a form of metadata, provide data about a program that is not part of the program itself. Annotations have no direct effect on the operation of the code they annotate. Annotations have a number of uses, among them:
â€¢ Information for the compiler â€” Annotations can be used by the compiler to detect errors or suppress warnings.
â€¢ Compile-time and deployment-time processing â€” Software tools can process annotation information to generate code, XML files, and so forth.
â€¢ Runtime processing â€” Some annotations are available to be examined at runtime.

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Q1889. Give an Example of Annotations ?

Ans. Suppose that a software group traditionally starts the body of every class with comments providing important information:
public class Generation3List extends Generation2List {

// Author: John Doe
// Date: 3/17/2002
// Current revision: 6
// Last modified: 4/12/2004
// By: Jane Doe
// Reviewers: Alice, Bill, Cindy

// class code goes here

}
To add this same metadata with an annotation, you must first define the annotation type. The syntax for doing this is:
@interface ClassPreamble {
String author();
String date();
int currentRevision() default 1;
String lastModified() default "N/A";
String lastModifiedBy() default "N/A";
// Note use of array
String[] reviewers();
}
The annotation type definition looks similar to an interface definition where the keyword interface is preceded by the at sign (@) (@ = AT, as in annotation type). Annotation types are a form of interface, which will be covered in a later lesson. For the moment, you do not need to understand interfaces.
The body of the previous annotation definition contains annotation type element declarations, which look a lot like methods. Note that they can define optional default values.
After the annotation type is defined, you can use annotations of that type, with the values filled in, like this:
@ClassPreamble (
author = "John Doe",
date = "3/17/2002",
currentRevision = 6,
lastModified = "4/12/2004",
lastModifiedBy = "Jane Doe",
// Note array notation
reviewers = {"Alice", "Bob", "Cindy"}
)
public class Generation3List extends Generation2List {

// class code goes here

}

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Q1890. What are few of the Annotations pre defined by Java?

Ans. @Deprecated annotation indicates that the marked element is deprecated and should no longer be used. The compiler generates a warning whenever a program uses a method, class, or field with the @Deprecated annotation.

@Override annotation informs the compiler that the element is meant to override an element declared in a superclass.

@SuppressWarnings annotation tells the compiler to suppress specific warnings that it would otherwise generate.

@SafeVarargs annotation, when applied to a method or constructor, asserts that the code does not perform potentially unsafe operations on its varargsparameter. When this annotation type is used, unchecked warnings relating to varargs usage are suppressed.

@FunctionalInterface annotation, introduced in Java SE 8, indicates that the type declaration is intended to be a functional interface, as defined by the Java Language Specification.

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