Beginning help with Java

darin3200 · 06-25-2003, 09:06 AM

I'm am trying to learning java and I hava a few questions. First, I go to download the Java Developers Kit. Should I donwload the JRE or SDK ? Secondly how do i install something that is .bin. And lastly, my book is written for windows users. Can anyone give me what to do in linux for the following.

C:\>javac Example.java (for compiling)
C:\>java Example (for running)

Thanks,

acid_kewpie · 06-25-2003, 09:16 AM

you want the sdk - Standard Developement Kit

.bin - run it, it's a self executable installer

the same programs will work.

jpbarto · 06-25-2003, 09:20 AM

You want the SDK (Software Development Kit). The JRE (Java Runtime Environment) is just for running java apps... not writing them.

to execute a .bin file the easiest way is to pass it to the shell...
sh j2sdk1.4.1_install.bin

and then finally the javac and java commands are the same on linux as on windows... just make sure that the jdk bin directory is in your path, that JAVA_HOME environment is setup and that your CLASSPATH is set up.

hope that helps,
jpbarto

darin3200 · 06-25-2003, 12:32 PM

Quote:

Originally posted by jpbarto
just make sure that the jdk bin directory is in your path, that JAVA_HOME environment is setup and that your CLASSPATH is set up.

Lost you here.

Here is what I have

Code:

/*
This is a simple, simple app.
This is called First.java.
*/
class First {
public static void main(string args[]) {
}
}

I save this as First.java in my home directory. How should I comply it with the >javac commmand.
Thanks,

jpbarto · 06-25-2003, 12:36 PM

compile with
javac First.java

run with
java First

are you aware of the two common java environment variables?
JAVA_HOME
and
CLASSPATH?

JAVA_HOME points to the directory where java is installed.
for example my java compiler and sdk and everything is installed in /opt/j2sdk1.4.1
so at the command line I execute
export JAVA_HOME=/opt/j2sdk1.4.1

then the CLASSPATH contains a list of directories where Java can find its lib files (or your executable code)
so you'd want something like...
export CLASSPATH=$JAVA_HOME/lib:./

darin3200 · 06-25-2003, 01:08 PM

this is what I am trying

Code:

[darinf@localhost darinf]$ javac First.java
bash: ./javac: Permission denied
[darinf@localhost darinf]$ su
Password:
[root@localhost darinf]# javac First.java
bash: javac: command not found
[root@localhost darinf]# export JAVA_HOME=/usr/java/j2sdk1.4.1_03/
[root@localhost darinf]# export CLASSPATH=$JAVA_HOME/lib:./

what should I try now?

Looking_Lost · 06-25-2003, 02:06 PM

export PATH=$PATH:/usr/java/j2sdk1.4.1_03/bin

try it with the bin at the end

string should be String if you get it going.

darin3200 · 06-25-2003, 02:33 PM

It doens't do anything, it just brings up another command prompt. Do I do >javac or just javac. And i always get a command not found with both. Do I have to have my code anyplace special like in /usr/java/j2sdk1.3.1_03/bin or can in just be in my home directory. Thanks for the help becaue I have no idea what I'm doing

Looking_Lost · 06-25-2003, 02:45 PM

Simple test just to get you doing something.

add in the line System.out.println("Whoopeee! ");
inbetween the two brackets after main

You'll have to be root

copy your code to the /usr/java/j2sdk1.4.1_03/bin directory

type

javac name_of_my_file.java
then
java name_of_my_file (without the java extension)

If you don't get any errors i.e javac not found then it's cool and all you've got to do is make sure for certain the directory above is in your path

darin3200 · 06-25-2003, 03:49 PM

no, that didn't help. So after I write the java, where should I save it to?

jpbarto · 06-25-2003, 05:11 PM

After you write the java you can save it to anywhere.
issuing the command
javac First.java
will work if the javac executable (which resides in the bin directory of your java installation) is in your PATH environment variable.
after you execute
export PATH=$PATH:/usr/java/j2sdk1.4.1_03/bin
then execute
javac --help.

If javac prints out its usage then your command shell can find the javac compiler.

next execute
javac First.java

darin3200 · 06-25-2003, 05:35 PM

Thanks, it works. I tried to complie first but it would show a little ^ where I was missing something and I finally got it working.

Code:

/*
This is a simple, simple app.
This is called First.java.
*/
class First {
public static void main(String args[]) {
System.out.println("Whopeeee!!! I wrote JAVA");
}
}

Its primative and simple but I love it. Of course I might dig up this thread later if I get confused.

Also, I found what I did wrong, I can only run javac from the /bin directory of my j2dk directory. Is there anyway around this?

Looking_Lost · 06-26-2003, 02:40 AM

Forgive me if I'm having a wry smile to myself but it's already being said a good few times now

To be doubly sure insert the line

PATH=$PATH:/usr/java/j2sdk1.4.1_03/bin

before the export PATH line

into /etc/profile file

logout of the gui

log back in again and it should be accessible by every user in their shell, hopefully.

darin3200 · 06-26-2003, 08:10 AM

yeh, wry smile all you want. Before I actually typed PATH=$PATH:/JAVA_HOME

and I was thinking how that didn't lool quite right.

Looking_Lost · 06-26-2003, 08:16 AM

Okey-dokey, it's good to keep a sense of humour about things. I'm the first to laugh at myself - which I need to do more often than not when there's a computer involved.