History
of java
In 1991, Sun Microsystems engineers led James
Gosling decided to develop a language for consumer device like (Cable boxes
etc). Consumers want to be hardware independent (means independent application,
suppose you develop a application software in windows but it not capable to run
on Unix) but hands on those person who free from these tenses. Since different
manufactures would use different CPUs, different systems configurations but
this language is ready to run on all platforms. The project as code name ‘GREEN’.
In this time, Sun microsystem uses UNIX for their project. We uses
C++ language in this project because c++ language was used ‘object oriented’. The original name of the language was oak. And later they changed the name(oak) to java in January 1995.
Finally, one big step was taken on 7 dec 1995 when Microsoft signed a
letter of interest with sun for java technology source license.
Where it used?
Probably Java is used.
1. Desktop
Application such as acrobat reader, Antivirus etc.
2. Web
Application
3. Enterprise
application such as banking application
4. Mobile
such as android and java ME
5. Embedded
system
6. Smart
card
7. Robotics
8. Games
etc.
Java is high level language. It is completely hardware independent
language means “write once, run anywhere and at anytime, forever”. Programs are
run by an interpreter that converts the byte code to the appropriate native
machine code.
Byte
code: byte code consists of optimized set of instruction
that are not specific to processor. We get byte code after compiling the java
program using a compiler called javac.
Native
code: native code is computer programming (code) that is
compiled to run with a particular processor and its set of instruction.
JVM,
JRE, JIT and JDK
JVM (java virtual
machine):- the bytecode is to be executed by java runtime environment (JRE)
which is called as java virtual machine. The program that are running on JVM
must be compiled into a binary format which is denoted by .class files.
The JVM execute .class or .jar files, by either
interpreting it or using a just in time compiler (JITc).
Note: the
JIT is used for compiling and not for interpreting the file.
1.
JVM is like a specification (map) of documentation.
2.
JRE is like a implementation of
document, it is not an open source.
3.
JDK (java development kit)- it is the
collection of JRE and package file.
Note: every
source code (.java) generate the .class file.
Firstly
we are install the jdk in our computer.
Path set: there
are two way of run the java program.
1. Computer
icon right click -> property ->advanced system -> environment variable
-> System variable -> new -> variable name is path and Variable value
is address of the bin file.
C:/program
files/java/jdk/bin
This the permanent method of path save of java
program. You can be save anywhere in computer and run program.
2. C
drives -> program file -> java -> jdk -> bin -> save the program.
Simple program
Class
A
{
Public
static void main(String arr[])
{
System.out.println(“hello”);
}
}
Compile
-> javac A.java
Execution
-> java A
BY
default java classes and packages are distributed in .jar format.
.jar
file is the compress format of the file.
Note: Java is open source. So you can check rt.java. it is the compress file
of classes and package. This is provided by sun microsystem as part of JDK.
C:\program
file\java\jdk\jre\lib\rt.jar
E:\jar
-> describe all keyword
E:\jar
–xf rt.jar
Void:
No return type. If there is an error in the program then o.s check it and give
the message.
Public
: JRE is the outside part of the class. JRE call the main method and access
specifier.
Static:
In a class there are two type of members.
1.
Instance Member
2.
Class Member
Instance
member: this member represent attributes
And behavior of
individual object.
Class
Member:- class member represent attribute & behavior of
the whole class.
Note:
static keyword denotes class members.
By default all the member
of a class are instance member.
Method:
first letter of each word except the first word of the method is capitalized.
print();
getPrioprity();
getKeyMathodMap(); etc.
String
arr[] : main method is to used command line
argument. It is represent I/P provided by command prompt with
name of command.
System:
it is the final class in java.lang
package. System class facility provided input, output, error, loading file
& library.
Out:
out is static member of the system class and is type printstream class.
Println:
it is the method of printstream class.
Example:
class printstream
{
Public void print(String
s)
{
-------
}
Public void
println(String s)
{
-------
}
Class system
{
Public static printstream
out;
{------
}
Author-Ravi Kumar
