So, we have learned about how to run Java
programs and then the different resources which are required to support your Java programming.
So, today we have a quick demo about setting our environment suitable for Java programming.
We in addition to this we shall discuss a few more things also. So, you should configure your machine right
if you use a laptop or any PC so, that you can run your programs from your project directory.
So, we should advise you to build a directory so, that you can store all the programs that
you will develop. And, then we will also learn about how a program can be edited and the
different steps towards the execution of your program. Finally, we shall have some simple
demonstration of simple small programs so, that you can understand how to deal with a
basic Java programming features. Let us have some demo, I understand that so,
yes. So, in the theoretical discussion, I have mentioned that you should install JDK
version 8. I hope you have already downloaded the JDK 8 and installed in your system. Now,
suppose you have installed your JDK software in program files. So, we will see exactly we have installed
in our own machine in program files directory the JDK system, you can see we have installed
our programs I mean JDK in program files directory; the name of the directory here is JDK. And,
this is the version where we have installed the JDK version 8 ok. Once the installation is successful you have
to set the path of your program directory; that means, the main directory where the all
the Java tools, Java codes, Java commands are installed. So, we have to do it I am giving
you the step by step. First you have to go to properties and then
you go to advanced settings and the environment variables and then you have to set the Java
home, the variable name JavaHome then the variable value for the Java home should be
set at the C://Program Files/Java/JDK 1.8.0_171, this is basically the program which you have
installed. So, you have to set this variable name Java home with this value. And then you have to set the path. So, the
path that you should set using this name that JAVA HOME then under the JAVA HOME the bin
because the bin is basically the executable of all the Java course, Java systems is there.
So, this is the setting of the parts and then finally, you have to set the classpath. So,
you can set the classpath variable by C://Program Files/Java/JDK 1.8.0_171/bin. So, this is
basically your executable or the common files where it will be is it will it is stored.
So, you have to set the paths: one the paths and then system variables are configured this
way, it will help you to run your program from any directory. So for example, in this case, we have created
one directory. The name of the directory is NPTEL Java>all final>week 1>code>demonstration
1. So, today we have created a directory we [ca/can] can call it as a project directory,
the name of the directory is demonstration 1. You can according to your own understanding
you can create your project directory anywhere in your machine, in your system, in any drive.
And, then once you do it you will be able to now create your program, compile your program
and executive your program. Now, I told you the Notepad++ is a very good
editor which you can consider to write your program. Now, I am just opening this Notepad++
software so, that you can see. So, here is basically opening the software
Notepad++ So, this is the window of the Notepad++. So, it is basically text editor you can type
anything whatever the things you can type from the keyboard. So, this is the simple
editor anybody can use it ok, our objective is to write a Java program; I am writing a
Java program. So, let us start Java program is like this
you just ok. See the Java program that I am going to write
it, I will not write it here through keyboard; I have already written for you I am just opening
this file. So, I am opening the programs in the first Java program. So, this is the first
program that we are going to have a demo. So, this is the program whose name is the,
it is class name is rather FirstJavaProgram. So, this program is now supposed you have
typed it from your keyboard then our next task is to save this program. So, there is
a save menu and you can go save menu save as so, let the FirstJavaProgram is saved.
So, this so, the program is saved and after saving you can go to your directory where
you can see the program is already saved here. For example, here FirstJava FirstProgram.java
is saved here ok. Once the program is written and saved successfully our next task is to
compile it. For this compiler, we have to go to the command
prompt. So, you have to go to the command prompt from your Windows system if it is there
and if we use the Unix system then you have to open a terminal so that you can use it
to type the command. Now, in order to compile your program the command that is required
is javac and then you have to give the full name of the file. The file that we have used
to save our first program is FirstJavaProgram.java. So, we have to give the name of the file in
the same way as the name of the class you have given and it is a case sensitive so,
be careful about that. So, this is the example where javac we have
invoked the compiler to compile the program FirstJavaProgram.java. Now, let us compile
it ok. So, as there is no error, no message in the command from this means that this program
has successfully compiled. Once on the successful compilation, you can see in the same directory
one file is created, the name of the file is the same as the name of the Java file except
the extension is .class. So, here you can see the byte code file which has been created
is FirstJavaProgram.class. So, one this program is successful on compilation
now we are ready to run it, to run this program the command that we said to use it java. So,
Java first program FirstJavaProgram and then .class you can use the .class or even if you
use the class also no issue so it will run. So, here, for example, the class file name
is FirstJavaProgram. So, just simply type java and the name of the class file, namely
FirstJavaProgram here. So, this is the program that has been executed and as you see this
program is basically used only one statement namely System.out.println() and within this
println() is basically typed the “Congratulations your first, just open or just browse. So, this is the message that it will display
“Congratulations your first Java program run successfully. Now, we can see that output
also gives the same thing. This is basically the steps that you have to edit your program,
compile your program using javac and then run your program using Java command. So, these
are the few steps that you should consider and now say, suppose there is a mistake in
this program. For example, you have given the name of the
class file FirstJavaProgram1, but you saved this program as a FirstJavaProgram.java saved
this program as a FirstJavaProgram.java right. So, yes this is the program that we have created,
but the see the name of the class file that we have created is FirstJavaProgram 1, but
the name of the file that we have saved it FirstJavaProgram.java. The two things are
not the same; this means that in this case compilation should not be successful.
Now, let us run the program the same javac FirstJavaProgram.java and then run it. No,
you have to no your program, no class file is what.
Different from the class file name. So, how it is compiled successfully?
Compilation will be done. The compilation will be successful.
Now, let us see run the program. So, to run the program java FirstJavaProgram right now
what is going on here, how the compilation will be successful. Why we have saved the
program as JavaProgram1.class. Yes.
Yes, now here we can see we have saved the program file as the name FirstJavaProgram,
but the name of the class that is there in the program is FirstJavaProgram1. So, there
is no match, if there is no match that means mismatch then the compilation will not be
successful. So, for example, in this case, we could not compile the program successfully.
So, here you should note that the name of the class file should be same as the name
of the Java file. Then, in that case, the program will be compiled successfully and
if it is successfully compiled then you will get some execute some if the execution will
be possible. Now, let us see I have another simple demonstration
of another program. So, HelloWorld yes so, this program and I am writing. So, I am writing
another program. Let us give the name of the program is helloworld.java program. So, HelloWorld
this is the program and it has only one statement,
it is very similar to the FirstJavaProgram. I will combine it so, javac this program has
been saved as helloworld.java. So, here the name of the file Java file is helloworld,
all in small letters helloworld.java. So, program compilation is successful then we
will be able to run it. So, running the program using Java right so, java helloworld . right
yeah; so it gives Hello, World. Now, in the same program I am adding one more statement
System out . println() System.out.println(). So, here instead of “Hello, World” I am
typing “Hi”. So, here the two messages: the first message “Hello, World” and the
second message “Hi” will be printed. I am again compiling and then again execution.
So, you see Hello, World and then Hi. So, you can understand about, if you want to print
some message on the screen the statement that is required in Java program is System.out.println().
And, whatever you write within double quote is basically print will display on the screen
; that means, as if whatever it is written there. So, Hi for example, again Hi . . . within
the double quote and the same thing Hi . . . right Hi . . . ok; now if you save it again run
it so, it is like this. Now, if you want to print two messages in
one println() statement so, we usually use plus symbol so, Hi plus no no Hi ++ Debasis
ok. So, now here basically in one line, it will print Hello, World then the next line
Hi and then Debasis will be printed you can see ok. So, now you have hope you have understood
that is a very simple statement and the simple program indeed. So, how you can run the simple
program? This is a good starting point for you actually ok. Now, let us consider another
program, this program is basically we have discussed how to define an array and then
how to initialize an array and how to use the element which is stored in an array. So, this is the one program that we have written
here the name of the program is TestArray, where capital T and then capital you should
note it. So, this is the name of the program your Java program and the and this program
should be saved as TestArray.java. So, this program has been saved as a TestArray.java
in the directory, the current project directory the test right. So, this is the program TestArray.java
we have stored it. Now, let us look at the program state statement
by statement, we have to understand this program what we have done it now ok. So, this is the
name of the class the TestArray, this is the name of the program and then public static
void main String args. It is as usual there the standard syntax that you have to follow;
you will understand the meaning of this statement later on.
Now, next is basically we have declared an array type of integer. So, int a within square
bracket and then it is basically initialization memory allocation and then declaration all
the three things have been done together. So, this is the statement int an array symbol
equals then within second brackets 10 20 30 40 50 so; that means, the array a is of now
size 5. And, this array contents 5 elements which are stored in a 0 location 10 a 1 location
20 a 2 location 30 a 3 location 40 and a 4 location 50. So, this array is stored and
then the next one for loop, this for loop basically we will print the elements which
are stored in the array. So, this loop will roll starting from i equals to 0 because the
array index is from 0 and then it will loop till value of i less than a.length().
So, a.length() is basically what is the size of the array a. So, a.length() is the specific
one function that you can use and that will return the size of the array. So, in that
case, a.length() is 5 and then the next is basically an implementation of the loop variable
i ++ and within this loop System.out.println(). So, it will print one element in the array
at a time and then go to the next loop and so on. So, this will print the array. So,
instead of println() if we type print it basically will print all the elements in one line. So,
ln and print the difference is that is basically in one line or in a different line.
Now, let us have the ln I will discuss simple print as an alternative to println() later
on. Now, once the array is array elements are printed our next step is to calculate
the average value of all the elements which are stored there in the array. So, we have
declared one variable called the sum and it declared as a float and then the average has
also a float variable. So, we declared two variables; one is the sum and the another
is average and sum is initialized a 0 at the time of declaration.
Now, so the next loop is to find the sum of all the elements and finally, it will basically
calculate the average is basically sum divided by the total number of elements stored in
the array that is the size of the array. And finally, there is a System.out.println() and
it will print the average value with this statement that average equals the average
value. Now, let us run this program using javac TestArray.java
is the program file name ok, run it run ok. So, this program is successfully compiled,
now we are going to run this program right. So, here you see the first few lines 10 20
30 40 50 is an outcome of the first for loop, it basically it display all the elements which
are stored there. And, the next for loop calculate the sum of all the elements the stored in
the array and finally, calculate the average which is printed within the System.out.println()
average equals to 30.0 in this case. Now, I will just want to do some changes here
in the first for loop, I am writing system out println() instead of println() simple
print and then let us see what will happen right run. So, it is little bit not easy to
difficult I can put some single space. So, I can go to the print again print a.i ++ and
then within double quote plus double quote blank space. So, if we give a space so, the
display will be quite comfortably visible. So, we make the print statement like this.
So now, here we can see how the output is displayable on the screen. I can make a little
bit different output at the end of the right System.out.println() at the first for loop,
at the end of the first for loop brackets you know here right here, here you can type
right one System.out.println(). System.out.println() just only brackets double quote right nothing
ok. I have so this semi colon so, I just see so
in the first for loop it will print all the numbers in one row, then at the end of the
for loop it will go to the next line and then in the next for loop it will calculate sum
and then print at the next line. So now, you see the display is more comfortably presentable
so, that you can see about it, yes now you can understand. So, this is the matter of
simple how you can configure your printing on the display. So, using System.out.println();
regarding this System.out we will learn a lot when we will discuss this method in details. So, let us come to another one example. In
this example, we will consider here the 3DArray. Now, let us give the name of this program
as a 3DArray as the file and you should save this program as a 3DArray.java. So, this program
if you see the name of the program file is 3DArray here public static void main String
args it is as usual ok. And, now we have declared here. So, here
we declared an array of type integer and we gave the name of the array as my3DArray. As
it is a 3DArray so, it should have 3 square brackets as it is shown here and then this
array will be declared and then memory allocation for this memory allocation, we use the keyword
new; new is basically the memory allocated. So, it will allocate the memory for the array
and here you see 3 4 5 are the 3 dimensions. So, the first dimension is for the number
of pages, the second is for the number of rows and the second next last dimension 5
is the number of columns. So, if it is a 2D array then is a 4 5, if it is a 3D array then
3 4 5 like so, 3 dimensions. So, it is basically is a collection of 3 2 dimensional array 3
2 dimensional arrays where each 2-dimensional array of size 4 rows and 5 columns. So, here
basically if we print it then it will print as a 3 2 dimensional arrays actually.
Anyway now, just let us see how we can initialize, there are you can read the total number of
elements which can be stored in this array is 60. So, 60 array typing from the keyboard
sometimes is very difficult anyway. So, we are just using one for 3 for loops to initialize
this array. Now, to initialize this array I use one I mean is the nested for loop I
should say, here see the nested for loop. This loop will roll for 3 loops actually the
innermost loop with k=0, k