3680 tutorial console

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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.




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:




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:




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.




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:




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.




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.




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:




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.




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.




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.

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