#RandomAccessFile

[jacob-cs]

original source : http://tutorials.jenkov.com/java-io/files.html

Files are a common source or destination of data in Java applications. Therefore this text will give you a brief overview of working with files in Java. It is not the intention to explain every technique in detail here, but rather to provide you with enough knowledge to decide on a file access method. Separate pages will describe each of these methods or classes in more detail, including examples of their usage etc.

Reading Files via Java IO

If you need to read a file from one end to the other you can use a FileInputStream or a FileReaderdepending on whether you want to read the file as binary or textual data. These two classes lets you read a file one byte or character at a time from the start to the end of the file, or read the bytes into an array of byte or char, again from start towards the end of the file. You don't have to read the whole file, but you can only read bytes and chars in the sequence they are stored in the file.

If you need to jump around the file and read only parts of it from here and there, you can use aRandomAccessFile.

If you need to jump around the file and read only parts of it from here and there, you can use aRandomAccessFile.

Writing File via Java IO

If you need to write a file from one end to the other you can use a FileOutputStream or a FileWriterdepending on whether you need to write binary data or characters. You can write a byte or character at a time from the beginning to the end of the file, or write arrays of byte and char. Data is stored sequentially in the file in the order they are written.

If you need to skip around a file and write to it in various places, for instance appending to the end of the file, you can use a RandomAccessFile.

Random Access to Files via Java IO

As I have already mentioned, you can get random access to files with Java IO via the RandomAccessFileclass.

Random access doesn't mean that you read or write from truly random places. It just means that you can skip around the file and read from or write to it at the same time in any way you want. No particular access sequence is enforced. This makes it possible to overwrite parts of an existing file, to append to it, delete from it, and of course read from the file from wherever you need to read from it.

File and Directory Info Access

Sometimes you may need access to information about a file rather than its content. For instance, if you need to know the file size or the file attributes of a file. The same may be true for a directory. For instance, you may want to get a list of all files in a given directory. Both file and directory information is available via the File class.

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Guidelines for Using Exceptions in Java

Note: Whitespace has been automatically removed by this site for all the code examples.

You may want to read and adopt the guidelines that help you get the most out of Java's exception handling mechanism. You can write powerful and effective Java code by adopting most, or all, of the things recommended here.

Remember that exception handling provides a way to process synchronous errors such as divisions by zero and out-of-range array indexes. It's not meant for handling asynchronous events such as disk I/O completions and mouse clicks and keystrokes.

When to use Exceptions You may be wondering as to how you actually decide to create and throw an exception. As a rule of thumb, create exception classes for all common exceptions that are likely to occur in multiple classes of an application. In order to deal with simple errors that are likely to occur only in individual methods, try not to create an exception class. You can use an if statement in most cases to trap these types of errors.

Here's a simple example that shows when not to use a try-catch block in your code. The code throws an error when there's an exception of the type NullPointerException.

try {

System.out.println(refvar.toString()};

}

catch (NullPointerException e) {

System.out.println("refVar is null!");

This is pure overkill. You can instead use the much simpler if statement to handle these types of simple errors.

if (refVar!=null)

System.out.println(refVar.toString()};

else

System.out.println("refVar is null");

If your code can perform a simple logic test, as shown here, to handle an error, do so, rather than using an exception object to handle the error.

When you neither catch nor throw exceptions When you call any method that throws a checked exception, you must either throw the exception or catch it. If you decide that you can't handle the exception in the method where it occurs, write a throw statement to send the exception up to the calling method, which must then either handle it with an exception handler, or throw it up to its calling method.

The following set of examples show how you must either catch or throw a checked exception, in order to avoid compiler errors.

The first example shows code that throws an IOException. The statement in the method getFileLength may throw an IO exception when it calls the constructor of the RandomAccessFile class. In addition, the statement that calls the length method of the RandomAccessFile object may also throw an IOException. You thus specify the throws clause in the declaration for the getFileLength method to trap IOException.

public static long getFileLength() throws IOException

{

RandomAccessFile in = new RandomAccessFile("mytext.dat", "r");

long length = in.length();

return length;

}

Our next example shows code for a method that calls the getFileLength method. Since we already know that the getFileLength method call throws an IOException error, our new method must either handle the IO Exception or throw it. Our example here shows how to handle the IOException by catching it with a try statement:

public static int getRecordCount()

{

try

{

long length = getFileLength(); // this may throw an IOException

int recordCount = (int) (length / /RECORD_SIZE);

return recordCount;

}

catch (IOException e) // this will catch the IOException

{

System.out.println("IO Exception!");

return 0;

}

}

The third example shows how a method can call the getFileLength method without catching IOException. Instead, it throws the exception.

public static int getRecordCount() throws IOException

{

long length = getFileLength(); //this may throw an IOException

int recordCount = (int) (length / RECORD_SIZE);

return recordCount;

}

The getRecordCount method here includes a throw clause, which ensures that any IOException is thrown up to the calling method.

Our fourth example shows what happens when you don't catch an exception or throw it.

public static int getRecordCount()

{

long length = getFileLength(); //this may throw an IOException

int recordCount = (int) (length / RECORD_SIZE);

return recordCount;

}

Since your code fails to catch or throw a checked exception, you'll receive a compile error:

MyExceptionTest.java.26: unreported exception java.io.IOException;

must be caught or declared to be thrown

The following is a quick summary of best practices and guidelines that enable you to take advantage of Java's exception handling mechanism, without succumbing to common missteps in the use of exceptions.

Begin Early It is a good idea to incorporate exception handling into your applications from the get go, before you even start programming. That is, you must do this at the design stage, as it gets much harder to do it after implementing your applications.

Don't Ever Ignore an Exception Regardless of whether you're dealing with a checked or an unchecked exception, don't ever ignore the exception. Sometimes, you might see code such as the following:

//Following is an empty catch block

try {

...

} catch (SomeException e) {

}

The empty catch block means that the exception is simply ignored - it's not dealt with. You don't want to do this in your programs. At the minimum, if you must really, really ignore the exception, put a comment explaining why you wanted to ignore the exception. You can use printStackTrace to output a simple error message to tell you there was a problem. If you ignore the exception, because of a condition that you've predicted, it means that the program will run on despite the error. However, you're going to run the risk of a complete program failure down the road when conditions change. If you propagate the exception out, you can ensure that the program fails quickly and captures information that helps you fix the error.

Don't use Exception Handling for every Statement The goal of exception handling is to clarify programs - try not to use a try/catch/finally mechanism for every potential exception generating statement. A simple strategy is to enclose a significant amount of code within the try block and specify multiple catch blocks to account for all possible exceptions. End the whole thing with a single finally block if you need to release any resources held by the program. In any case, avoid placing try/catch/finally around each statement that might throw an exception. Your goal is to use exception handling to remove error processing code from the main program code.

Maintain Failure Atomicity Always strive to ensure that when an object throws an exception, the object continues to remain in a well-defined and usable state. Ideally, even after a method fails due to an exception, the object should be left in the state it was before the method was invoked, When a method can do this, it's said to possess the property of failure atomicity.

You can achieve failure atomicity by using any of the following programming techniques.

Design Immutable Objects The easiest way to achieve failure atomicity is by designing immutable objects. Although when you create an object you can change its contents, occasionally, it's a good idea to create objects whose contents cannot be changed after creation. An object such as this is called an immutable object and its class, an immutable class. A good example is the String class, which is an immutable class. You get automatic failure atomicity when an object is immutable, because the state of an object can't be modified after you create the object.

Check Parameters for Validity before the Operation If you're stuck with mutable objects, the best way to achieve failure atomicity is to perform a check for the validity of parameters before the program commences the modification of an object. The following example shows how you do this:

public Object pop() {

if (size == 0)

throw new EmptyStackException();

Object result = elements[--size];

elements[size] = null; // Eliminate obsolete reference

return result;

}

The initial size check ensures that the method will do two things when it tries to pop an element from an empty stack: it will throw an exception and it will do so while leaving the size field in a consistent state. Otherwise, the attempt to pop the element from an empty stack will leave the size field in a negative state which, of course, is an inconsistent state for the object to be in.

Attempt to Execute the Code before you Modify the Object You can write your programs in a way where the code that is susceptible to a potential exception, is run before any code that modifies an object. A good example would be where you would like to add an element to a TreeMap, wherein the new element must be compared using the TreeMap's ordering. If your code attempts to add an incorrect type element, it will fail when a search for the element in the tree is made, before the tree is modified.

Intercept the Failure Another strategy to achieve failure atomicity is to put in code that intercepts a failure that occurs during an operation, and which rolls back the object's state to what it was before the operation began. This strategy is often adopted when modifying disk based data, that is, data contained in a relational database, for example.

Perform Operations on a Temporary Copy of the Object You can limit state changes made to an object by changing a temporary copy of the object. You replace the contents of the object with the temporary copy once you complete the computational operations. If, for some reason, the computational work (say, a sort) ends up failing, no harm is done to the original object, as you're working with just a copy of the object.

Collect Failure Details If you're troubleshooting an easily reproducible failure, it's no big deal whether you're collecting detailed failure information. When dealing with exceptions that are not easily reproducible, it is critical that your exception's toString method captures sufficient details about the failure - to help diagnose and fix the failure.

When an exception occurs, your details message of an exception should capture the current values of all parameters and values that contributed to the exception. If your error message simply states IndexOutofBoundException, it's only of limited use and may, or may not, help you fix the data problem. If, on the other hand, your detail message for the IndexOutofBoundException contains the lower and upper bounds and the index value, you have something meaningful in your hands with which to proceed towards a fix of the failure condition.

Since the stack trace of the exception always contains the precise file and line number that threw the exception, you don't need a lot of information about the source code in your exception messages. To ensure that your exceptions always contain adequate failure details in their details message, use one of the constructors I explained about earlier in this chapter. It is better to do this than to capture the details within a simple string detail message.

The following example shows how you can use a more helpful constructor than the simple String constructor.

/**

* Construct an IndexOutOfBoundsException.

*

* @param lowerBound the lowest legal index value.

* @param upperBound the highest legal index value plus one.

* @param index the actual index value.

*/

public IndexOutOfBoundsException(int lowerBound, int upperBound,

int index) {

// Generate a detail message that captures the failure

super("Lower bound: " + lowerBound +

", Upper bound: " + upperBound +

", Index: " + index);

// Save failure information for programmatic access

this.lowerBound = lowerBound;

this.upperBound = upperBound;

this.index = index;

}

Top Tip: Provide accessor methods for all exceptions, especially for checked exceptions.

As mentioned earlier, it's sometimes useful to provide accessor methods to capture details regarding exactly why a failure happened. In the case of the example just shown, you can, for example, provide accessor methods for lowerBound, upperBound and index. It's critical that you provide such accessor methods for all accessor methods.My site list to string in java

Use Standard Java Exceptions As discussed earlier in the book, the Java platform offers a built-in set of unchecked exceptions which will take care of most of your exception mechanism setting needs. Make a point to try and use these preexisting exceptions before you run off coding your own custom exceptions. Other programmers are familiar with these preexisting exceptions and, therefore, they can easily understand your code. Also, since you'll be using just a set of basic exception classes and not a whole bunch of custom exceptions, your programs need less time to load.

Here are brief descriptions of the most common standard Java exceptions.

IllegalArgumentException

You throw this exception when a caller passes in an argument with an inappropriate value. For example, a calling program that passes a negative number in a parameter that denotes how many times you repeat an action.

IllegalStateException

This is the exception thrown when an object is illegally invoked because of its state - say, when a calling program tries to use an object before it has been initialized.

NullPointerException

Used when a parameter value is null when it ought not to be.

IndexOutofBoundsException

An exception thrown when a caller passes an out of range value in a parameter representing an index into a sequence.

ConcurrentModificationException

Thrown when an object designed for single thread usage finds that it was, or is, being concurrently modified.

UnsupportedOperationException

Thrown when an object doesn't support a specific operation such as when a program tries to delete an element from an append-only list.

Although in most cases it's quite apparent as to which exception applies to an error condition, sometimes, you may find that more than one exception might be correctly used for an error condition. There aren't any cut and dry rules for the specification of exceptions - as with some other things in Java, handling exceptions is an art as well as a science!

Document All of a Method's Exceptions Spend the necessary time to fully document all exceptions thrown by each method in an application. Declare all checked exceptions individually and use the Javadoc tag @throws to document the conditions under which each of the exceptions can be thrown.

It is critical that you don't fall into the bad habit of declaring that a method throws some super class of multiple exception cases that the method is set up to throw. That means that you never declare a method that can throw the generic exception classes Exception or Throwable! Using generic exceptions might handle the exception all right, but it keeps you from understanding the precise error that caused the exception to be thrown.

Top Tip: Always attempt to document every single exception that can potentially be thrown by each method in a program. 

Take care to document both checked and unchecked exceptions. Since unchecked exceptions normally represent programming errors, documenting them can keep you from avoiding those errors. You can use the same Javadoc tag @Throws to document unchecked exceptions, as is the case for checked exceptions.

If multiple methods in a class can throw the same exception, you may document the exception once in the class's documentation comment. This is much more efficient than documenting the exception separately for each of the methods.

Finally, a useful rule of thumb when handling Java exceptions is to always throw early and catch late!

This finally wraps up our discussion of Java's exception handling mechanisms and how to make the best use of them in your code. Our next topic is the effective use of pre and post conditions in your code within the framework of what's called Java assertions, primarily as a way of testing code before you move it to production.

[freemanjulie]

map framework in Java

There are three primary ways of implementing the map framework in Java:

Hash Map: This JAVA Framework allows the implementation of hash table data structures. Elements in Hash Maps are stored in key/value pairs.

TreeMap: This JAVA framework allows the implementation of tree data structures. It provides accessibility to the Navigable Map interface.

LinkedHashMap: This framework allows the implementation of linked lists and hash tables. It extends to the HashMap class where its entries are stored in a hash table.

Stack, queueing and sorting using JFC: In Java Foundation Classes (JFC), stacks are abstract linear data types with predefined boundaries or capacities. They follow a certain order when adding or deleting elements. In linear data structures, components are organized in a straight line, meaning, if one removes or adds an element, the data structure will decrease or increase respectively. Stacks follow a LIFO (Last In First Out) or (FILO) First In Last Out technique of sorting elements, meaning, the last item is always the first one to be removed.

Graph structures and algorithms

Graphs are non-linear data structures comprising of nodes and edges. Sometimes, the nodes are also called vertices. Edges are simply the arcs or lines that connect nodes within the graph. In Java Assignment Help, graph algorithms are a given set of instructions that connect nodes together. Based on the type of data, an algorithm can be used to identify a specific node or even a path between two nodes. Graphs are important in modeling and solving real-world problems Linear and non-linear searching algorithms. Searching is a common action in business applications. It involves fetching the information stored in data structures like maps, lists, arrays, etc. to help the business in decision-making. In most cases, the search action determines how responsive a given application will be for the end-user. Programs written in Java use several types of search algorithms, the most common being linear and non-linear searching algorithms. The linear algorithm is used to identify elements in an array by looping over other elements of the array. The non-linear algorithm is mostly used with sorted arrays to identify various elements and usually returns the index of the found elements or a negative one if there is no index found.

RandomAccessFile

The Random Access File is a class in Java  And Java Assignment Help used to write and read random access files. Basically, a random access file acts as a relatively large array of bytes. File pointer, a cursor applied to the array is used to perform the read-write operations and this is done by moving the cursor. If the program reaches the end-of-file and the required number of bytes have not been reached, then an EOFException is performed. In Java And JAVA Assignment Help, the Random Access File supports several access modes, which include, the read mode and the read and write mode. To read a byte, one must implement the read () method, and this will read a byte located in a position that is currently directed by the file pointer.

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Complete BeginnersStudents with programming experience who want to learn Java Course content of Become A Professional Java Developer From Scratch: Total Lecture:81 How To Study This Course Downloading and setting up our environments Variables Numeric operations and String concatenation Augmented Assignment Operators and Increment and Decrement Operators Getting Input from the user Displaying Current time Assignment The if statement Nested If-else statements Switch statement Logical Operators Using if-else statement to controll the input from the user Conditional Expressions Loops Nested Loops Using loops to controll the user input Assignment Classes Constructors with parameters Methods Static, final and scope of a variable Visibility Modifiers Data encapsulation Passing objects to methods Assignment Introducing arrays Processing arrays For each loop Arrays and methods The Arrays class Multidimensional arrays Assignment Inheritance Super, overriding and overloading The Object class Primitive and Reference variables The equals method The protected modifier and preventing Extending and Overriding Assignment Abstract Classes Interfaces Assignment Exceptions Getting information from exceptions and throwing our own exceptions The finally clause The File class Writing and reading data Reading data from the web Assignment FileInputStream and FileOutputStream DataInputStream and DataOutputStream BufferedInputStream and BufferedOutputStream ObjectInputStream and ObjectOutputStream RandomAccessFile class Assignment JFrame Adding a button to our JFrame Layout Managers Using JPanel as a subcontainer Helper Classes Image Icons Other components Listeners and Inner classes Alternative ways to create listeners Mouse Listeners and Mouse Adapters The Timer class Simple Login App More GUI Components Processing JComboBox and JList JScrollBar and JSlider CardLayout, BoxLayout and Box JTabbedPane Menus Dialogs JColorChooser and JFileChooser Assignment ArrayList and LinkedList Stacks, Vectors, Sets and Maps Note About Collections 6 more sections Become A Professional Java Developer From Scratch course Read the full article

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Module 1: Introduction

Java Why? What? How? When? Where?

Different Java Versions.

How Java is different from other Technologies

Module 2: Introduction To Java Programming Environment

How to Install & set Path.

A Simple Java Program

Compiling & executing Java Program

Phases of Java Program

Analysis of a Java Program

Understanding Syntax and Semantic Error,

Runtime Exception

Name of a Java Source File

Platform Independency

Java Technology (JDK, JRE, JVM, JIT)

Features of Java

Text Editors

Consoles

Module 3: Fundamentals of Java Programming

Naming convention of Java language

Comments

Statements

Blocks (Static, Non-static/instance)

Identifiers

Keywords

Literals

Primitive Data Types, Range

Reference (User defined) Data type

Variables (Primitive, Reference)

Type Casting, Default Value

Operators

Program/Interview questions

Module 4: Control Structures

Working with Control Structures

Types of Control Structures

Decision Control Structure (if, if-else, if else if, switch –case)

Repetition Control Structure (do –while,while, for)

Program/Interview questions

Module 5: Input Fundamentals And Datatypes In Java

Java program inputs from Keyboard

Methods of Keyboard inputs

Scanner, Buffered Reader

Problem Solving

Java Array

What is Array

Array Declaration in java vs C and C++.

Instantiation of an Array

String vs character array.Accessing Array

Elements, Default Value, for-each loop, varargs

Length of an Array (What is –Array Index Out Of Bounds Exception)

Increasing, Decreasing the Size and Copy of an Array

Multi-Dimensional Arrays

Program/Interview questions

Program/Interview questions Difference between C and C++ with Java

Application Compilation and Run

Interview related Question and Answer

Module 6: Object Oriented Programming (Oops Concepts In Deep)

Procedural Vs Object Oriented Program

Different type of Program Procedural Vs Object Oriented.

Top Down Vs Bottom Up Approach

Introduction to Object Oriented

Abstraction, Encapsulation, Inheritance,

Polymorphism.

Introduction to Classes and Objects

Custom Class Definition

Instance and Static Variables

Different ways to create Object Instance

Instance Variable and it's role in a Class

Constructors, types of Constructor,

Constructor Rule, Constructor Overloading

Static Variable and it's use.

Methods and their behavior.

Constructor vs Methods

Constructors

“this” Keyword

Java Access Modifiers (and Specifiers)

Programming Interview related Question and Answer

Call by value, Call by reference

Module 7: Command-Line Arguments

What is a Command-Line Argument?

Java Application with Command-Line Arguments

Conversion of Command-Line Arguments

Passing Command-Line Arguments

Using methods (Static , Non Static)

Loading...

Module 8: Integrated Development Environment

Using various Editors

Program Compilation, Execution in Editor

Using Eclipse IDE

Project Set Up

Source File Generation

Application Compilation and Run

Module 9: Inner Class

First View of Inner Class

Outer Class Access

Types of Inner Class

Module 10: Inheritance

Complete concepts of Inheritance

Sub-Classes

Object Classes

Constructor Calling Chain

The use of "super" Keyword

The use of “private” keyword inheritance.

Reference Casting

Module 11: Abstract Classes and Inheritance

Introduction to Abstract Methods

Abstract Classes and Interface

Interface as a Type

Interface v/s Abstract Class

Interface Definition

Interface Implementation

Multiple Interfaces' Implementation

Interfaces' Inheritance

How to create object of Interface

Module 12: Polymorphism

Introduction to Polymorphism

Types of Polymorphism

Overloading Methods

Overriding Methods

Hiding Methods

Final Class and Method

Polymorphic Behavior in Java

Benefits of Polymorphism

“Is-A” vs “Has-A”

Association Vs Aggregation

Interview related Question and Answer.

Module 13: Package

Package and Class path and its use

First look into Packages

Benefits of Packages

Package Creation and Use

First look into Class path

Class path Setting

Class Import

Package Import

Role of public, protected, default and private w.r.t package

Namespace Management

Package vs. Header File

Creating and Using the Sub Package

Sources and Class Files Management

Module 14: Using Predefined Package & Other Classes

Java.lang Hierarchy

Object class and using toString(), equals(),hashCode(), clone(), finalize() etc

Using Runtime Class, Process Class to play music, video from Java Program

Primitives and Wrapper Class

Math Class

String, StringBuffer, StringBuilder Class

String Constant Pool

Various usage and methods of String,StringBuffer, StringBuilder

Wrapper Classes

System Class using gc(), exit(), etc.

Module 15: New Concepts In Package

Auto boxing and Auto unboxing

Static import.

Instance of operator.

Enum and its use in Java

Working with jar

Module 16: Garbage Collection

Garbage Collection Introduction

Advantages of Garbage Collection

Garbage Collection Procedure

Java API

Interview related Question and Answer

Module 17: Exception Handling

Introduction to Exceptions

Effects of Exceptions

Exception Handling Mechanism

Try, catch, finally blocks

Rules of Exception Handling

Exception class Hierarchy, Checked &

Unchecked Exception

Throw & throws keyword

Custom Exception Class

Chained Exception.

Resource handling & multiple exception class

Interview related Question and Answer.

Module 18: Multithreading

Introduction

Advantages

Creating a Thread by inheriting from Thread class

Run() and start() method.

Constructor of Thread Class

Various Method of Thread Class

Runnable Interface Implementation

Thread Group

Thread States and Priorities

Synchronization method, block

Class & Object Level Lock

Deadlock & its Prevention

Inter thread Synchronization

Life Cycle of Thread

Deprecated methods : stop(), suspend(),resume(), etc

Interview related Question and Answer

Module 19: Input and Output Streams

Java I/O Stream

I/O Stream - Introduction

Types of Streams

Stream Class Hierarchy

Using File Class

Copy and Paste the content of a file

Byte Streams vs Character Streams

Text File vs Binary File

Character Reading from Keyboard by Input Stream Reader

Reading a Line/String from Keyboard by Buffered Reader

Standard I/O Streams Using Data Streams to read/write

primitive data

PrintStream vs PrintWriter Using StreamTokenizer and RandomAccessFile

Interview related Question and Answer

Module 20: Serialization

Introduction to Serialization

Using Object Streams to read/write object

Transient Keyword

Serialization Process

Deserialization Process

Interview related Question and Answer

Module 21: Collection Framework

Generics(Templates)

What is generic

Creating User defined Generic classes

The java.util package

Collection

What is Collection Framework

List, Set & Map interfaces

Using Vector, Array List, Stack,

Linked List, etc.

Using Collections class for sorting

Using Hashtable, Hash Map, Tree Map,

SortedMap, LinkedHashMap etc.

Iterator, Enumerator.

Using Queue, Deque, SortedQue, etc.

Using HashSet, TreeSet, LinkedHashSet etc

Using Random class

Using Properties in a Java Program

Using user defined class for DataStructure

Using Date and Formatting Date class.

Interview related Question and Answer

Module 22: Advanced Java Syllabus

Module 1: JDBC

Introduction to JDBC

Databases and Drivers

Types of Driver

Loading a driver class file

Establishing the Connection to different

Database with different Driver

Executing SQL queries by ResultSet, Statements , Prepared Statment interface.

Using Callable Statement

Transaction Management & Batch Update

Programs/Interview related Question and Answer

Module 2: JSP

· Basics Of Jsp

Life cycle of JSPJSP APIJSP in Eclipse and other IDE'sPrograms/Interview related Question and Answer.

· Scripting Elements

scriptlet tagexpression tagdeclaration tagPrograms/Interview related Question and Answer.

· Implicit Objects

outrequestresponseconfigapplicationsessionpageContextpageexceptionPrograms/Interview related Question and Answer.

· Directive Elements

page directiveinclude directivetaglib directivePrograms/Interview related Question and Answer.

· Exception Handling

· Action Elements

jsp:forwardjsp:includeBean classjsp:useBeanjsp:setProperty & jsp:getPropertyDisplaying applet in JSP

· Expression Language

What is expression and how to use itDefine expression and use over the service flowThe way to be achieve same in JSP

· Mvc In Jsp

MVC patternWorking flow implementation of MVCCRUD operation using MVCDesign a real time web application using MVC

· JSTL

Discussion on the tag libraryHow to implement and use

· Custom Tags

Custom Tag : What and Why?Custom Tag API?Custom Tag ExampleAttributesIterationCustom URI

Module 3: Servlet

Basics of Servlet

Servlet: What and Why?

Basics of Web

Servlet API

Servlet Interface

GenericServlet

HttpServlet

Servlet Life Cycle

Working with Apache Tomcat Server

Steps to create a servlet in Tomcat

How servlet works?

servlet in Myeclipse

servlet in Eclipse

servlet in Netbeans

· Servlet request

Servlet Request methodsRegistration example with DB

· Servlet Collaboration

Request Dispatchersend Redirect

· Servlet Configure

Servlet Configure methodsServlet Configure example

· Servlet Context

Servlet Context methodsServlet Context example

· Session Tracking

CookiesHidden Form FieldURL RewritingHttpSession

Loading...

Module 4: Concurrent and implementation of collection

Implemenation of ArrayList

Implemenation of LinkedList

Implemenation of HashMap

Implementation of Queue/PriorityQueue/Deque

Module 5: Advanced Multi-Threading

Implemenation of Executor pool service and working mechanism with real time

Big file(Single , multiple ) processing using multiple thread

Implemenation to achieve thread class and runnable interface

Module 6: Javamail

Sending Email

Sending email through Gmail server

Receiving Email

Sending HTML content

Module 7: Design Pattern

Singleton

DAO

DTO

MVC

Front Controller

Factory Method

Abstract

etc

Module 8: Junit

JUnit: What and Why?

Annotations used in JUnit

Assert class

Test Cases

Module 9: Maven

Maven: What and Why?

Ant Vs Maven

How to install Maven?

Maven Repository

Understanding pom.xml

Maven Example

Maven Web App Example

Maven using Eclipse

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Related Search Term

Java Training in Dubai

Which is the best institute for Java training in Dubai?

Core and Advanced Java Training Institute in Dubai

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Java Training Locations in Dubai

Site Galleria branches in Dubai are listed above. And most popular locations where students / professionals are lining up to get trained with us.

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Design Patterns - Adapter Pattern

Adapter Pattern

Also known as Wrapper.

Definition

The Adapter pattern is used to translate the interface of one class into another interface. This means that we can make classes work together that couldn't otherwise because of incompatible interfaces. A class adapter uses multiple inheritance (by extending one class and/or implementing one or more classes) to adapt one interface to another. An object adapter relies on object aggregation.

Where to use

•When you want to use an existing class, and its interface does not match the one you need. •When you want to create a reusable class that cooperates with unrelated or unforeseen classes, that is, classes that don't necessarily have compatible interfaces. •When you want to increase transparency of classes. •When you want to make a pluggable kit.

Benefits

•Highly class reusable. •Introduces only one object

Drawbacks/consequences

When using Java, Target must be an interface.

Adapter Pattern - Class Diagram

In the class-diagram above: •A Client class expects a certain interface (called the Target interface) •An available interface doesn't match the Target interface •An Adapter class bridges the gap between the Target interface and the available interface •The available interface is called the Adaptee

Adapter Pattern Example

public interface FileManager { public String open(String s); public String close(); public String read(int pos, int amount, byte[] data); public String write(int pos, int amount, byte[] data); } import java.util.*; import java.io.*; public class FileManagerUtil { private RandomAccessFile f; public boolean openFile(String fileName) { System.out.println("Opening file: "+fileName); boolean success=true; return success; } public boolean closeFile() { System.out.println("Closing file"); boolean success=true; return success; } public boolean writeToFile(String d, long pos, long amount) { System.out.print("Writing "+amount+ " chars from string: "+d); System.out.println(" to pos: "+pos+" in file"); boolean success=true; return success; } public String readFromFile(long pos, long amount) { System.out.print("Reading "+amount+ " chars from pos: "+pos+" in file"); return new String("dynamite"); } } public class FileManagerImpl extends FileManagerUtil implements FileManager { public String close() { return new Boolean(closeFile()).toString(); } public String open(String s) { return new Boolean(openFile(s)).toString(); } public String read(int pos, int amount, byte[] data) { return readFromFile(pos, amount); } public String write(int pos, int amount, byte[] data) { boolean tmp= writeToFile(new String(data), pos, amount); return String.valueOf(tmp); } } public class FileManagerClient { public static void main(String[] args) { FileManager f = null; String dummyData = "dynamite"; f = new FileManagerImpl(); System.out.println("Using filemanager: "+ f.getClass().toString()); f.open("dummyfile.dat"); f.write(0, dummyData.length(), dummyData.getBytes()); String test = f.read(0,dummyData.length(), dummyData.getBytes()); System.out.println("Data written and read: "+test); f.close(); } }

Imagine you need to develop a simple file manager to handle text documents. There is an existing resource that already handles this, but by some reason you are forced to a specific interface for your file manager. By using a class adapter we can use the forced interface and still reuse the existing functionality. In the class diagram below the interface FileManager is the target (desired interface). FileManagerUtil is the existing utility class that we would like to adapt to FileManager interface. We do the actual adaptation in the class FileManagerImpl, this class uses the desired interface and the existing functionality through inheritance, i.e. a class adapter. When FileManagerClient is executed the result is:

c:>Opening file: dummyfile.dat c:>Writing 8 chars from string: dynamite to pos: 0 in file c:>Reading 8 chars from pos: 0 in fileData written and read: dynamite c:>Closing file

Usage example

The Java API uses the Adapter pattern, WindowAdapter, ComponentAdapter, ContainerAdapter, FocusAdapter, KeyAdapter, MouseAdapter, MouseMotionAdapter.

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Java Tutorial : Java IO (Java RandomAccessFile - V1)

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Java Q/A Part XV

Java Q/A Part XV

What is the purpose of the enableEvents() method? The enableEvents() method is used to enable an event for a particular object. Normally, an event is enabled when a listener is added to an object for a particular event. The enableEvents() method is used by objects that handle events by overriding their event-dispatch methods.

What is the difference between the File and RandomAccessFile classes?