Session - 3 / Overview of JAVA

Introduction (10minutes)

Java Buzzwords (15 minutes)

Java Tokens (20 minutes)

Assessment (5 minutes)

Java Buzzwords

JAVA TOKENS

RESERVED KEYWORDS

Keywords are the reserved words which are enlisted here->

IDENRTIFIERS

Literals

Operators

Separators

Introduction to Java

•  Java was invented by James Gosling, Patrick Naughton, Chris Warth, Ed Frank and Mike Sheridan at Sun Microsystems, Inc. in 1991. It took 18 months to complete the first working version of Java.

•  This language was initially called as Oak but was renamed as Java in 1995.

•  Java is purely an object oriented programming language as its supports various features like Classes, Objects, abstraction, inheritance and polymorphism.

Java Buzzwords

Java is getting popular because of its features. Following is a list of buzzwords that makes Java a popular programming language.

•  Simple

•  Secure

•  Platform independent

• Object oriented

•  Distributed

•  Portable

•  High performance

•  Robust

•  Multithreaded

•  Interpreted

•  Dynamic

Let us discuss these features in detail.

1. Java is simple and small programming language

•  Java is a simple programming language. Even though you have no programming background you can learn this language comfortably.

• The programmers who worked on C or C++ can learn this language more efficiently because the syntax of Java resembles with C and C++.

 In fact Java is made more clear and adaptable than C++.

2. Java is robust and secure

• Following are reasons that make Java more secured than other programming languages

1. Java does not support the concept of pointers directly. This makes it impossible to accidentally reference memory that belongs to other programs or the kernel.

2. The output of Java compiler is not executable code but it is a bytecode. The instructions of bytecode is executed by the Java Virtual Machine(JVM). That means JVM converts the bytecode to machine readable form. JVM understand only the bytecode and therefore any infectious code can not be executed by JVM. No virus can infect bytecode. Hence it is difficult to trap the internet and network based applications by the hackers.

3 In programming languages like C or C++ the memory management is done explicitly by the user. That means user allocates or deallocates the memory. Whereas in java its automatically done using garbage collection. Thus user can not perform the memory management directly.

4. If an applet is executing in some browser then it is not allowed to access the file system of local machine.

3. Java is a platform independent and portable programming language

•  Platform independence is the most exciting feature of Java program. That means programs in Java can be executed on variety of platforms. This feature is based on the goal - write once, run anywhere, and at anytime forever.

•  Java supports portability in 2 ways - Java compiler generates the byte code which can be further used to obtain the corresponding machine code. Secondly the primitive data types used in Java are machine independent.

4. Java is known as object oriented programming language

•  Java is popularly recognised as an object oriented programming language.

• It supports various object oriented features such as data encapsulation, inheritance, polymorphism and dynamic binding.

• Everything in Java is an object. The object oriented model of Java is simple and can be extended easily.

5. Java is multithreaded and interactive language

•  Java supports multithreaded programming which allows a programmer to write such a program that can perform many tasks simultaneously.

• This ultimately helps the developer to develop more interactive code.

6. Java can be compiled and interpreted

• Normally programming languages can be either compiled or interpreted but Java is a language which can be compiled as well as interpreted.

•  First, Java compiler translates the Java source program into a special code called bytecode. Then Java interpreter interprets this bytecode to obtain the equivalent machine code.

• This machine code is then directly executed to obtain the output.

7. Java is known for its high performance, scalability, monitoring and manageability

• Due to the use of bytecode the Java has high performance. The use of multi-threading also helps to improve the performance of the Java.

• The J2SE helps to increase the scalability in Java. For monitoring and management Java has large number of Application Programming Interfaces(API).

• There are tools available for monitoring and tracking the information at the application

level.

8. Java is a dynamic and extensible language

•  This language is capable of dynamically linking new class libraries, methods and objects.

•  Java also supports the functions written in C and C++. These functions are called native methods.

9. Java is a designed for distributed systems

• This feature is very much useful in networking environment.

• In Java, two different objects on different computers can communicate with each other.

. • This can be achieved by Remote Method Invocation (RMI). This feature is very much useful in Client-Server communication.

10. Java can be developed with ease

There are various features of Java such as Generics, static import, annotations and so on which help the Java programmer to create a error free reusable code. 

Structure of JAVA Program 

JAVA TOKENS

The smallest individual and logical unit of the java statements are called tokens. In Java there are five types of tokens used. These tokens are -

1. Reserved keywords

2. Identifiers

3. Literals

4. Operators

5. Separators

RESERVED KEYWORDS

Keywords are the reserved words which are enlisted here->

IDENRTIFIERS

Identifiers are the kind of tokens defined by the programmer. They are used for naming the classes, methods, objects, variables, interfaces and packages in the program. 

1. The identifiers can be written using alphabets, digits, underscore and dollar sign. 2. They should not contain any other special character within them.

3. There should not be a space within them.

4. The identifier must not start with a digit, it should always start with alphabet.

5. The identifiers are case-sensitive. For example -

int a; int A;

In above code a and A are treated as two different identifiers.

6. The identifiers can be of any length.

Literals

Literals are the kind of variables that store the sequence of characters for representing the constant values. Five types of literals are -

1. Integer literal

2. Floating point literal

3. Boolean literal

4. Character literal

5. String literal

As the name suggests the corresponding data type constants can be stored within these literals.

Operators

Operators are the symbols used in the expression for evaluating them.

Separators

For dividing the group of code and arranging them systematically certain symbols are used, which are known as separators. Following table describes various separators.