I have an application that is opened by the terminal. It loads some data automatically and now I need to be able to use commands such as -new or -min or -help within the terminal with functionalities implemented in my Java code. So I need to define new parameters for my command line (which only work during the runtime of my apllication).
I tried to search it for several hours now but all I get are tips how to run java programs with my command line...
So I am pretty stuck right now and hope you can help me out.
I am thankfull for every answer.
All the command line arguments for your program are passed to the main method in that method's only parameter, the string array (typically named args).
You can parse this array manually, or feed it to a library like Getopt to handle all of that for you.
Related
For one of our projects for school, we're asked to create a command-line executable program representing a hypothetical school grades system for teachers. We can use any language we want and I chose to use Java. However, with a Jar file executable, I'm not able to freely use the command line in Linux to use the methods I've created. It only runs through the commands I've written in the Main Java file and then exits. I suppose I can run a scanner but that seems tedious to scan and pick out my variable arguments to pass into methods.
Am I missing something? Or did I make the wrong language choice?
Thanks!
You can make an indefinite loop in your main which will get the input from console using BufferedReader (recommended) or Scanner.
Then, you could use a Scanner to tokenize de input and check whether the input corresponds to a command using a switch/case.
I'm a noobie to Java and I had some questions, I think they may be easy (duh) answers to you experts but for me, I couldn't figure out the answer.
What is the point of Java programs, all I am making in my class now are simple read text files, have user input some stuff on the command line and the program prints out something. Like, it's cool and all that I can make a program do this but what does this all lead up to?
Say, I create a java program that converts celcius to fahrenheit and I want to have someone use it. Would I be able to get someone to use it that has no knowledge of Java, that is to say, giving it to my mom and she can run it from her computer without using Eclipse? How do I have someone who has no knowledge of coding run my program?
And my last question is, what is the point of command line arguments? Instead of putting them in the arguments, why not just have it in the code itself? Is it because if the code is big, it might be hard to find it? And if I download code that requires argument input, is it possible to download the code with the arguments set in Eclipse or would I have to manually do it?
Thanks, sorry for the long paragraph, but just wanted to put my thoughts down.
I think the short answer is modularity. Compiling or building a Java program takes time and knowledge (like you mentioned, someone who has no knowledge of Java probably wouldn't know what to do).
Passing in command line arguments allows you to just send someone the binary distribution of your program and passing in their own parameters without having to know what your code looks like or have to modify it.
In real life, programs aren't run from Eclipse (obviously), they're usually packaged into jars or wars and executed from the command line or some kind of app server.
If you download code that requires command line arguments, you will probably have to put them into Eclipse yourself, but hopefully the application has some documentation or help usage that explains what the arguments should look like.
You can create your own jar files that you can run from the console.
One of the simpliest ways to make your program usable without using Eclipse is with the Windows command prompt or Linux terminal:
go to you working directory (where your java file is stored)
Type javac (Example:javac hello.java) -This would compile your program
Type java (Example: java hello) - This will start it
Using of args is when you want to set some information to your program with the launching of the program.
Another way to start your program without using Eclipse is to make your own executable jar. With this you will get something like .exe file From which you can start your aplication
Most of the java programs are started from the CMD / terminal, or runs on java servers. There are aplication which have their own user interface (SWING, SWT, AWT ...) .
Most popular types of Java usage is creating a serious bussiness software, android aplications, complex web aplications etc.
what is the point of command line arguments?
Benefits of using Command line.
if I download code that requires argument input, is it possible to
download the code with the arguments set in Eclipse or would I have to
manually do it?
Right Click on project-name > Run > Run Configuration > select Arguments tab
For more info click here.
What is the point of Java programs, all I am making in my class now
are simple read text files, have user input some stuff on the command
line and the program prints out something. Like, it's cool and all
that I can make a program do this but what does this all lead up to?
This is just the begining. Learn Java core. Get familiarized with Java. One day you will be building tools using Java. eg:- Apache
How do I have someone who has no knowledge of coding run my program?
Compiling a java program into an executable
Before you do any this, get a book on Java (my fav - Java The Complete Reference) and read it. Learn how Java works, why is it different from other languages, best practices etc...
After 2-3 years from now, you'll get the importance of taking a small step by building simple cmd line programs using Java
I'm very new to all Java related programming. For a school assignment, I've created my Java application using BlueJ. Apparently, the application should be able to run from the command prompt with the following line:
myapp -compress fileName
Honestly, I don't have the slightest idea about how to setup such:
My application has a Main class. Am I supposed to change it to be called myapp?
I've been running my app with java Main compress filename. I see that now I shouldn't be using the java key. But of course, as it is now, it won't work if I remove it. How can I run the app without it?
Is there a difference between having the compress argument I always use and the -compress one they tell me? Is that dash (-) any special?
Looking at this page: http://docs.oracle.com/javase/1.4.2/docs/tooldocs/windows/java.html, it seems to insist that to run my program I do need to use the java key. And the dash seems to be used for something called options - there are standard and non-standard. However, there doesn't seem a way to make a "custom" one (-compress).
So my question is, how can I run my application with the above format?
The easiest way it to create a one-line shell script (if you're using Unix) or a one-line batch file (if you're using Windows). Call it myapp (or myapp.bat) and make it launch Java, passing the appropriate arguments.
As to the -compress argument, your main() takes an argv. You'll need to examine that to figure out what arguments have been passed to your program. You can either code everything yourself (very easy in your case), or use an existing framework:
How to parse command line arguments in Java?
Trying to figure out my way around Sphinx 4 (the CMU speech recognition engine in Java), I tried to use a demo included with the distribution by altering it to what I wanted it to do (the name of the demo is Aligner). I am running into problems and want to use jdb from the command line for debugging the same. I read the documentation given here, but it is limited and does not have a solution to my problem, which in brief is as follows:
I invoke jdb like so:
jdb Aligner (name of the main class of the project).
Set a breakpoint like so: stop at Aligner:33
The output I get (on the command line):
Deferring breakpoint Aligner:33.
It will be set after the class is loaded.
In the file demo.xml (which is the makefile equivalent for this Project),
javac debug=true is mentioned.
My questions:
1. Where should I invoke jdb from? Should it be invoked from anywhere in the entire sphinx directory or should I invoke it from the same directory as Aligner.java?
2. How can I use jdb with the jar for this project?
P.S: I know I can use Eclipse with this, but I am not sure I know how to do that. My first priority is to get this up and running.
P.P.S: I am a Java newbie and do not know much about the language. My preference for the command line comes from my background of C/C++ programming on the command line.
Any help is most welcome,
Thanks!
What are you actually trying to do?
If you are not so familiar with Java, why not use Sphinx3 or pocketsphinx, both of which are implemented in C?
http://cmusphinx.sourceforge.net/wiki/download/
Also, you might get better responses on this topic by checking the forums on the above site, or checking in to the IRC channel #cmusphinx
Finally, you mention that your program name is 'aligner', which makes it sound like maybe you are trying to do forced alignment? There are already existing tools for this in the sphinx3/sphinxtrain/pocketsphinx packages and it would probably be worth your while to check them out.
I would just like to know whether it is possible to make a command prompt in Java.
My friend asked to make it, I wanted to know if it was possible or not. If it is possible, can someone suggest me some api or something? Thank you.
EDIT: I want to make it similar to windows command prompt
EDIT 2: I would like to make a SWING GUI application and put a command prompt inside of it.
Yes. Use the Process API.
You can run commands in Java using the Process API. You can also get the output and write input to the runned process. For more info, see this tutorial.
But if you want to make a terminal emulator (such as those in Linux) in Java,
I recommend having a look at JCTerm or JTA.
You must be careful how you start it.
If you start your program with java.exe then the console (input/output) is shown. With System.out.println("mymessage"); you can print (output) text to the console. With System.in you can read from the console. This delegates to the java.io.Console class (available throug System.console()).
If you start your program with javaw.exe, then you don't see the console. You must then create your own screen to allow input/output. This is the default on Windows.
Java can do console I/O and it can launch processes, so yes, it's possible. You'd use methods of System.in and System.out to display a prompt and read commands, and a ProcessBuilder to execute programs.
yes it's possible in java
your have to do some research on Java.lang & IO
Check the class java.lang.Runtime. It provides a couple of exec() methods.