3680 tutorial console
TRANSCRIPT
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BCIS 3680 Enterprise Programming Console Tutorial ‐ 1
BCIS 3680 Enterprise Programming
Instructor: Dr. Andy Wu
Tutorial: Running Java in Command Console
Although we will use NetBeans to compile and run Java applications most of the time, the ability to
use command console to compile and run Java applications is essential to learning Java. Here I will
show you step by step how to do just that.
1. Starting a Command Console
First, let’s start a command console. There are two ways to do that. You may click Start | Run:
Then, in the “Run” dialog box, type in cmd. Click “OK”.
Alternatively, you may click Start | Accessories | Command Prompt to start a command console.
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BCIS 3680 Enterprise Programming Console Tutorial ‐ 2
Either way, a command console will appear. Yours may have white characters on black background.
To make my screenshots easier to read and to save toner, I have changed its color scheme.
2. Basic Commands
There are
a few
terms
you
want
to
know
to
get
started
with
the
console.
First,
note
the
prompt
ends
with a greater‐than sign (>). The part before it indicates your working directory at this moment. By
default, and as shown above, the working directory is the current user’s home directory. In this
example, it is C: \ Document s and Set t i ngs\ Andy.
In Windows Explorer, each directory is represented by a folder. So the previous directory would
look something like this:
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BCIS 3680 Enterprise Programming Console Tutorial ‐ 3
If the
current
working
directory
of
the
command
console
does
not
have
the
files
you
want
to
work
with, you may use a few commands to move around the file system.
If the directory (namely folder) you want to work with is not on the same drive as the current
working directory, you may move to that drive first. In our example, my Java source code file is
stored in F: \ j avademo\ hel l o\ sr c. So I type in F: and then press Enter.
Note that the working directory is now the root of the F: drive. Next, I use the cd (change directory)
command to move to the j avademo directory.
Notice that once I issue the cd command, the working directory now changes to F: \ j avademo:
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Another useful command is dir (directory), which lists the contents within a directory.
In the output of dir command, subdirectories (subfolders) are indicated by <DI R>. However, there
are two “subdirectories” (. and . . ) that exist in every single directory on the file system. They have
special meanings and don’t appear in Windows Explorer as folders. So you can ignore them. Thus,
the above output shows that there is a subdirectory called hel l o under F: \ j avademo , which is true.
However, my Java source code file is in F: \ j avademo\ hel l o\ sr c. So I keep on moving until I am
in the
sr c
directory.
There,
I find
my
Hel l o. j ava
file.
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BCIS 3680 Enterprise Programming Console Tutorial ‐ 5
In fact, I don’t have to issue the cd command repeatedly to get to the directory. If I know exactly
where I want to go, I can get there with one single cd command after I am in the right drive:
3. Running Java Commands
An idiosyncrasy of command prompt is that, unless you do something (and we will cover that in the
next section), only a small number of most essential commands are recognized by the console by
default. Most of these commands are related to system maintenance. If you issue a command that is
not one of those, the console will look in the current working directory to find it. Since a command
in fact is an executable file (most often a . exe file), the console looks for the executable file that has
the same name as your command. If it finds a match, the executable file is run. Otherwise, the
console simply tells you that the command is not recognizable and stops.
Unfortunately, the
Java
compiler
file
( j avac. exe)
is
not
recognized
by
the
console
automatically.
If
I am inside my source code directory and issue the javac command, it will not be recognized:
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BCIS 3680 Enterprise Programming Console Tutorial ‐ 6
That’s because the console searched the current working directory F: \ j avademo\ hel l o\ sr c and
didn’t find an executable file with the name j avac. exe.
The console will recognize the javac command if I change my working directory to where
j avac. exe is
(the
Java
binary
folder).
On
my
machine,
the
location
is
D: \ J ava\ j dk1. 6. 0\ bi n:
Another problem surfaces, though, when I issue the javac command from this directory:
This time the console does not complain about not finding the javac command. However, since I
am now in D: \ J ava\ j dk1. 6. 0\ bi n , not F: \ j avademo\ hel l o\ sr c , where I have my source code files, I encounter a “f i l e not f ound” error. In other words, when I run the Java compiler in the
console with the syntax javac source_file_name , the console looks in the working directory for
both j avac. exe and the source file. Usually, these two files are stored in different directories and it
is bad practice to do otherwise. Thus, it looks like I have a dilemma here. Regardless of which of
the two directories I am in, either the console can’t find the j avac. exe file or my source file.
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BCIS 3680 Enterprise Programming Console Tutorial ‐ 7
4. Changing the System Path Variable
There is an easy and a hard way to solve the dilemma. The hard way is to issue the command from
the Java binary folder and also, in the second part of the command, tell the console where to locate
the source code file by preceding the file name with the complete path to that file.
As shown above, the command went through and now there is a Hel l o. cl ass file in the directory.
This would not be a problem if I were just compiling one or two source code files. But obviously, if I
have to do it for many times, that will be a lot of typing to do.
There is an easier solution. All I need to do is to add the path to the folder where j avac. exe is
installed on
my
system
to
Windows’
PATH
variable.
To
do
that,
first,
right
click
the
“My
Computer”
icon on Windows desktop and select “Properties”.
Alternatively, I can click Start | Settings | Control Panel | Performance and Maintenance. Then click
the “System” icon.
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BCIS 3680 Enterprise Programming Console Tutorial ‐ 8
If you work with Windows Vista, the desktop may be darkened and you may be prompted for
confirmation. Agree to it to move ahead.
Either way, the System Properties dialog box will appear. Click the “Advanced” tab:
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BCIS 3680 Enterprise Programming Console Tutorial ‐ 9
Click the “Environment Variables” button. The “Environmental Variables” dialog box will pop up:
In the “System variables” area (in the bottom), scroll down to find the “Path” variable. Click it and
then click the “Edit” button. The “Edit System Variable” dialog box will appear.
Initially, the entire content of the “Variable value” textbox is highlighted. To prevent altering any
part of it inadvertently, I would press Ctrl + C to make a copy of it and paste it into Notepad as a
backup copy. Then I move to the very end of the value and get my cursor there:
Next, I add a semicolon (; ) to it. A semicolon separates one part of the path from the next. Then I
add the location of my Java binary folder (namely D: \ J ava\ j dk1. 6. 0\ bi n , where j avac. exe is)
to it. In essence, I am appending this location to the system PATH variable.
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BCIS 3680 Enterprise Programming Console Tutorial ‐ 10
Click “OK” several times until you get all the way out to the desktop. You can check whether this
has been done successfully by issuing the path command in the console:
As it’s shown above, now the location of the Java binary folder is part of the PATH variable (if it isn’t,
reboot the computer). The significance of this is that, from now on, the console should be able to
recognize the javac command, regardless of which working directory I issue the command from.
5. Running Java Commands Again
Now, I should
be
able
to
move
into
my
source
code
file
directory
and
issue
the
javac
command
from there. The console will find my . j ava file there and since javac is now recognizable, the
command should go through. To see the impact of changing the PATH variable clearly, let’s delete
the Hel l o. cl ass file created by the solution in the previous section. Then, take a look at the
content of the directory again.
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As shown above, only Hel l o. j ava is in the source file directory. From here I issue the javac
command:
The console doesn’t complain any more. The compiler produces the Hel l o. cl ass file gain. Let’s
run it by issuing the java command.
The . cl ass file works. Since j ava. exe resides in the same folder as j avac. exe (see the first
screenshot on page 6), the command console also recognizes the java command from anywhere.