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This is a Java programming class that runs on Java-enabled SERVER or application server and EXTENDS the capabilities of servers that host applications.

A servlet POSSESSES all the features of Java such as PLATFORM independence, portability, security and database connectivity.

By being platform independent, we mean that the java source code can be run on all OS. The PRESENCE of a machine independent code CALLED Byte Code, which once compiled, can be run on any platform, makes Java platform independent.

The compiler feature in Java CONVERTS or translates the high-level language into a common format understood by all the machines. The only REQUIREMENT is the AVAILABILITY of JVM.

A Collection in Java is a group of individual OBJECTS that are REPRESENTED as a single unit. The Collection Framework in Java defines CLASSES and interfaces that represent a group of objects as a single unit.

The TWO MAIN root interfaces are Collection interface and Map interface.

It is a class that is declared with an ABSTRACT keyword. An abstract class can have both abstract and non-abstract METHODS and needs to be EXTENDED. In this class, the METHOD must be implemented and cannot be instantiated.

Similar to CLASS, an interface in Java is a reference type. An interface contains ABSTRACT methods, CONSTANTS, STATIC methods, default methods and nested types.

A class implements an interface and INHERITS the abstract methods of the same interface. Writing an interface is like writing a class.

Method Overloading allows a class to have more than one methods of having the same NAME, but only if the argument LISTS are VARYING. This feature is similar to CONSTRUCTOR overloading feature that allows more than one constructor to a class only if their argument lists are DIFFERENT.

It is one of the features of OBJECT-oriented programming that allows the developers to perform one action in different WAYS. Developers OFTEN USE POLYMORPHISM in referencing a parent class to a child class object.

It is the process when one class acquires the properties or methods or fields of another class. This process is used to arrange and MANAGE INFORMATION in hierarchical ORDER. The class that inherits the properties is called SUBCLASS. The class whose properties get INHERITED is called superclass.

It is a reference VARIABLE that REFERS to the CURRENT OBJECT. It can be used as follows:

• To refer instance variable of class
• To invoke class constructor
• Passed as an argument in METHOD call
• Passed as an argument in the constructor call
• Used to return a class instance

The constructor is a method USED to initialize an object. A normal java method has return type but the constructor does not have any explicit return type. It is called during the object creation time.

There is two type of Constructors - DEFAULT or no-arg Constructor, Parameterized Constructor.

It is a PROTOTYPE or user-defined BLUEPRINT that is used to create objects or data types. A CLASS represents PROPERTIES or methods that are common to objects of ONE type. All class objects possess the class properties.

Following are the advantages:

• Allow you to define packages for BUNDLING a group of CLASSES or interfaces.
• No name conflicts with other package names.
• Packages MAKE access CONTROL easier
• Packages make access control easier

CLASS LOADERS are responsible for dynamically loading the classes during the runtime to the JVM. They are a part of the JRE.

Three types of Class Loaders are built-in - BOOTSTRAP, Extensions and SYSTEM.

It is a virtual machine that ENABLES computers to run JAVA programs in addition to programs written in other languages but are compiled to Java bytecode. OpenJDK project has developed the Java virtual machine (JVM) REFERENCE as open source code. The reference includes a JIT compiler which is KNOWN as HotSpot.

JAVA Programming language was created by James GOSLING at SUN micro systems in 1991.

Java is a computing PLATFORM as well as a programming language. An object-oriented language, Java is a fast, secure and easily extendible language. Java is a platform independent and Architecture-neutral language.

It is used to create COMPLETE & POWERFUL applications that may run on a single computer or be distributed among clients and servers in a network. I ALSO can be used on the intranet applications.

Java.lang.Throwable

An anonymous class is like a LOCAL class or an inner class, but WITHOUT a name. You can USE an anonymous class for declaring and INSTANTIATING a class simultaneously.

In Java, there are various STATES of a THREAD. But at any POINT of time, it can exist in any ONE of these states:

• New
• Runnable
• Blocked
• Waiting
• Timed Waiting
• Terminated

For copying an OBJECT in Java, there are TWO WAYS- shallow COPY and deep copy.

System.exit(0);

It refers to writing programs or applications that RUN across multiple devices when the devices are connected on a network.

The java.net package CONTAINS a collection of INTERFACES and classes that communicate and allow programmers to write programs that FOCUS on solving the current PROBLEM.

It is one endpoint of two-way COMMUNICATION between programs that are running on the same network.

A SOCKET is tied to a port number in such a manner that the TCP layer can recognize the application where the data needs to be SENT. If you USE Socket instead of native CODE, your programs will communicate platform-independently.

In Java, there are three ways to GENERATE random NUMBERS:

• java.util.Random CLASS
• Math.random method
• ThreadLocalRandom class

This is DONE USING java.util.Random class:
import java.util.Random;
Random rand = new Random();
int n = rand.nextInt(100) + 1; //100 is the maximum and the 1 is our minimum.

• Simple and EASY to learn
• Platform Independent
• Supports is OBJECT ORIENTED PROGRAMMING language
• Robust and multithreaded
• Enables high performance
• Java Interpreted
• Secure and its interpreter
• Follows WORA (write once, run anywhere) approach