Language:
It is the Mediator. Without language we cannot
communicate with others.
There are 2 types of languages.
Natural language
Programming language
Natural language
Programming language
Natural language:
If u want to establish the communication between 2
humans
Programming language:
If u want to establish the communication between
human and system
E.g.: c, c++, java, .net
Smallest word of the statement is called token
Collection of tokens is called statement
Collection of statements is called program
Collection of programs is called software
Note: each programming language follows syntax and
semantics rules
Each program has tokens :- They are keywords,
identifier, operators, values/constants, and separators
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IDENTIFIER: A
name of Class,variable,method and labels is called an identifier.
Rules for constructing identifier:
a. Identifier must starts with either alphabets(a-z,A-Z) or _ (underscore) or $
b. From 2nd character onwards either alphabets or _ or $ or digits(0-9)
c. don't take any keyword as identifier.
d. Identifier doesn't allow any special characters.
Ex: Total(valid) total123(valid) 123total(invalid) _total (valid)
Total#(invalid) total_number(valid) total-number(invalid
Ex: Total(valid) total123(valid) 123total(invalid) _total (valid)
Total#(invalid) total_number(valid) total-number(invalid
=========================================================================================
RESERVED WORDS:
53 reserved words are there in java
50 are keywords
3 reserved literals(true,false,null)
Keywords
for Primitive Datatypes: 8
byte short int long
float double char boolean
Keywords
for flow control: 11
if else switch case default for
do while break continue return
Keywords
for Modifiers: 11
private protected public static abstract final volatile transient native strictfp(jdk1.2)
Class
related keywords: 6
class interface package extends implements import
Object
related keywords:4
new instanceof super this
Keywords
for Exception Handling: 6
try catch finally throw throws assert(jdk 1.4)
void
Unused
keywords:2
const goto
New
keyword in jse 1.5(version): 1
enum
Reserved
Literals: 3
true false null
==========================================================================================
JAVA VERSIONS:
No. of Version code
name
--------------------------------------------------------------
Jdk 1.0/sdk 1.0 oak
Jdk 1.1 ---------
J2SE1.2 playground
J2SE 1.3 kestrel
J2SE 1.4 Merlyn
JSE5 Tiger
JSE6 Mustang
JSE7 Dolphin
============================================================================================
JAVA
|
|
-------------------------------------------------------------------------------------------------------
| | |
| | |
JSE JEE JME
============================================================================================
JAVA
|
|
-------------------------------------------------------------------------------------------------------
| | |
| | |
JSE JEE JME
============================================================================================
JAVA FEATURES
-----------------------------
1. Simple
2. Object oriented
3.Platform Independent
4.Portable
5.Architecture
6.Multi-Threading
7.Robust
8.Compiler and Interpreter
9.N/w based
10. Dynamic
11.Distributed
12.Secured
OOP LANGUAGE
------------------------
Object based language and object oriented language
difference
Q. What are conditions to call one language is pure oop's?
A). 1. Encapsulation
2. Abstraction
3. Polymorphism
4. Inheritance
5. All predefined types are objects (java not
support)
6. All operations are performed by sending messages
to objects
7. All user defined type’s objects
Ex:ruby,small talk,Eiffel
Q. What is difference between loosely and strongly typed coupled languages?
A) C,c++,java,.net this are strongly typed languages
because before uses of variable it's type.Declaration is very important
without type declaration we cannot able use that variable more over it can be
supporting related values only JavaScript is loosely typed language the variable
declaration is not compulsory and it can be able to handle any type of values
Var a;
a=10;
document.write (a);
a="cherry";
========================================================================================
Data Types:
Java having 2 types of data types: they are
1. Primitive data type
2. Reference data type
PRIMITIVE TYPES:
Java having 8 primitive data types. They are
Numeric DataTypes:
Floating Point DataTypes: float double
Non-Numeric DataTypes: char boolean(for logical values)
==========================================================================================
byte :
Size: 8
bits or 1byte
Range: -128
to 127
This datatype is the best suitable if you are
handling data of streams from a file or network
byte b=100; //valid
byte b=200; //invalid
Compile time error: possible
loss of precision
Found:int
Required: byte
=========================================================================================
short :
Size: 16
bits or 2bytes
Range: -2^15 to 2^15-1 i.e. -32768 to 32767
This data type is very rarely used types in java but
best suitable for 16 bit processors.
========================================================================================
int :
Size: -32
bits or 4 bytes
Range: -2^31 to 2^31-1 or
-2147483648 to +2147483647
In C language the size of int is varied from
platform to platform.
The C program worrest for 32 bit processor cannot
run on 16 bit processor. Hence the chance of failing of c program is very high
of we change platform.As a result C is not considered as Robust Language But in
the case of java the size of any data type is fixed for any platform,hence the
chance of failing the java program very less As a result java is considered as robust language
========================================================================================
long :
Size: 64 bits or 8 bytes
Size: 64 bits or 8 bytes
Range: -2^63 to +2^63-1
If int is not enough for to hold big values like
amount of distance traveled by light in 1000 days we should for long data type
========================================================================================
Floating point data type:
float size: 4 byte or 32 bits
float range: -3.4 e 38 to 3.4 e 38
double size: 8 bytes or 64 bits
double range: -1.7 e 308 to 1.7 e 308
These datatypes are representing for real numbers.For 6-7 decimal places of accuracy we should go for
float data type so this less accuracy.For 14-15 decimal places of accuracy we should go
for double datatype so this is more accuracy.float is single precision where as double is double precision
========================================================================================
boolean :
The size of the boolean is not applicable (It purely
depends on the underlying JVM)
Range: not applicable(But allowed values are true or false)
TRUE or FALSE are not violation leads
CTE: cannot resolve the symbol
==========================================================================================
char :
Size: 2
bytes
This is provide il8n. Providing Unicode’s for all the worldwide character
sets(range 0 to 65535)
=========================================================================================
Reference Data
type:
We can take the any
user define class or predefined class as data type
The default value
for reference data type is null
============================================================================================
class:
class is a template, it contains variables and methods
it is just a imagination so class does not exist physically
By using class keyword we can define classes in java
class <class name
(identifier)>
{
Variables;
Methods;
}
Example: class Student //Student is class name
{
int sno; // sno , name are variables
String name;
public void read() // read() is method name
{
System.out.println("Student is Reading");
} // method close
} // class close
=========================================================================================
Object:
u The instance of the class is called object
u Each object contains state (instance variables), Behavior (methods), Reference (name)
u By using new keyword we can create the objects in java
Syntax:
Classname object
name = new Classname();
Example :
Student s1= new Student(); // here " s1" object name and Student is classname
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JVM ARCHITECTURE :
=======================================================================================
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