Java: Java Programming For Beginners a simple Start To Java Programming (Written By a software Engineer)

Environment
A  complete  set  of  variables  and  the  values  they  contain  form  what  is  called  the
environment.  Therefore,  whenever  you  load  a  new  webpage  in  the  browser,  you  are
creating  a  new  environment.  If  you  take  the  example  of  Windows  8,  it  creates  an
environment  when  an  application  starts  and  the  same  is  destroyed  when  the  application
ends.
Functions
A set of statements that solve a purpose are referred to as a function. The purpose of using
functions is code reuse. If your program uses functionality multiple times in the program,
then it is implemented as a function, which can be called as and when required. Since, a
function is to be called from within the code, parameters can be sent to the function from
the code. Upon execution, the function returns a value to the calling function. The syntax
for function declaration and definition is as follows:
function multiply(a, b){
return a*b;
}
The  name  of  the  function  must  always  be  preceded  with  the  keyword  function.  The
variables a and b are parameters passed into the function and the function return the value
obtained  by  computing  a*b.  This  is  a  simple  function,  but  you  can  implement  complex
and large function depending upon the functionality desired.
Now  that  you  have  implemented  the  function,  you  must  be  wondering  as  to  how  the
function is called. Here is an example:
var x=2;

---

var y=5
var c=multiply(x, y);
Here, x and y are arguments that the function multiply will receive as parameters.
JavaScript  is  a  loosely  typed  language.  What  that  means  is  that  if  you  pass  more
arguments  to  a  function  than  what  it  is  expecting,  the  system  simply  uses  the  first  n
arguments  required  and  discards  the  rest.  The  advantage  of  this  functionality  is  that  you
can use already implemented functions and pass the extra argument to scale the function
and add functionality to it. On the other hand, you will not be able to get any indication of
error if you unintentionally pass the wrong number of arguments.
JavaScript  also  provides  some  built-in  functions  for  interacting  with  the  user.  These
functions are as follows:
alert
This function raises an alert with a message and the system resumes operation after
the user clicks on the OK button. Sample implementation:
alert(‘Alert message!’);
prompt
This function presents a textbox to the user and asks him or her to give input. You
can supply the default value in the presented textbox and the user can click on the
OK button to accept that the value entered is correct. Sample implementation:
var result = prompt(‘Enter a value’, ‘default value’);
confirm
This  message  gives  the  user  the  choice  to  OK  or  CANCEL  an  action.  Sample
implementation:

---

var result = confirm(‘Do you wish to proceed?’);
Function Scope
Each variable that you declare possesses a scope of operation, which is the function within
which  the  variable  has  been  declared.  This  is  called  the  local  scope.  Unlike,  many  other
languages,  which  define  local  scope  by  the  curly  braces  within  which  the  variable  lies,
JavaScript’s local scope is same as function scope.
In addition to this, JavaScript also supports the concept of global scope, in which variables
can be declared global and thus, can be used anywhere in the program.
Nesting Functions
Functions can be nested at any level. In other words, a function can be called from within
another  function,  which  could  have  been  called  from  a  different  function.  However,  it  is
important  to  note  that  the  scope  of  variable  is  within  the  function  in  which  they  are
declared.