I am quite new to Java so this might be quite simple for others.
I'm making a text summarizer by following a tutorial and I came across a slight problem. When I run my program, it outputs "Usage: java Main input.txt keywords ...". So it follows the code "if(args.length < 1)" to do that. However, how do I change it so it reads the text file and carry on with the program.
generatesummary class works perfectly.
if(args.length < 1){
System.out.println("Usage: java Main input.txt keywords ...");
return;
}
String filePath = args[0];
if(filePath == null){
filePath = "./input.txt";
}
String[] keywords = null;
if(args.length < 2){
keywords = new String[1];
keywords[0] = "";
}
else{
keywords = new String[args.length-1];
for(int i=1; i<args.length; i++){
keywords[i-1] = args[i];
}
}
System.out.print("keywords:\t");
for(String keyword : keywords){
System.out.print(keyword+"\t");
System.out.println();
}
//String[] keywords = null;
Generator generator = new Generator();
generator.loadFile(filePath);
generator.setKeywords(keywords);
generator.generateSignificantSentences();
System.out.println(generator.generateSummary());
generator.generateSummary();
}
}
It is a simple check to see whether the user has given at least one argument when launching the application or not. args.length gives the length of the array that holds the command line arguments. To be able to run it, you need to provide a fileName as an argument - that's what the error is suggesting.
So in a command line you would write something like java Main filename.txt for it to be able to pass the check.
args.length provides the length of the arguments sent to the Java application. If args.length < 1, that means no argument was sent to it.
You need to send in the file name that you want your application to process. If you're running Java from the command line, you can just add the file name to the command, such as "java Main file.txt".
Also note that if you're using an IDE to do your development, such as Eclipse, you'll need to send in the argument (file name) in a way that is particular to that IDE. You should consult the help for that IDE, or post here.
Lastly, you can directly just code in the file name in your program, instead of having to send it in through the command line. Get rid of the if(...) statement checking args.length, and change filePath declaration to:
String filePath = "/path/to/filename.txt";
Good luck and best wishes on your Java learning endeavor!
Your main method is like main(String[] args). Now, when you tried to run that class you typed following command I guess.
java classname
So in this case args will not contain anything. But if you type
java classname fielName
args will contain the file name and it will not go inside of the first if block. Because length og args is 1.
I understand you are executing that code inside a main method. The main method has the next signature:
public static void main(String[] args){
...
}
This method is your applications entry point in java. Watching it's signature you can see that it receives an argument named args that is an array of String's. As the main method is the entry point, this arguments come from the place you are executing the application (terminal, IDE, etc). lenght is and attribute of java arrays, that stores the number of elements that array has. By executing if(args.length < 1) you are checking if you received less than one argument, because the code is expecting a filename as argument. Yo have to execute your code form a terminal as the second line says
System.out.println("Usage: java Main input.txt keywords ...");
For adding arguments in eclipse you have to put them into "Run > Run Configurations...> Arguments". This article explains it perfectly: cs.colostate.edu/helpdocs/eclipseCommLineArgs.html
Related
I am a novice at coding but cannot understand why it runs fine on my machine, but when I upload my code I get a "NoSuchElementException" on line 19, "String command = keyboar.next();" I understand it has to do something with closing the scanner but I cannot figure out any other way to work it so it loops the print screen and input. Especially since it works fine when I run it on my machine.
Any insight is much appreciated here
import java.util.Scanner;
public class example1
{
public static void main(String[] args)
{
System.out.println("Enter an ending value");
Scanner keyboard = new Scanner(System.in);
int input;
input = keyboard.nextInt();
while(true){
System.out.println("Count up or down?");
String command = keyboard.next();
if (command.equalsIgnoreCase("up")) {
int one = 1;
int ten = 11;
int hund = 101;
while (one <= input) {
System.out.printf("%5d %4d %4d\n", one, ten, hund);
one++;
ten++;
hund++;
}
}
if (command.equalsIgnoreCase("down")) {
int neg = -input;
int one = -1;
int ten = 9;
int hund = 99;
while (one >= neg) {
System.out.printf("%5d %4d %4d\n", one, ten, hund);
one--;
ten--;
hund--;
}
}
}
}
}
You've created a scanner that reads from System.in. You don't close it anywhere, so I'm not sure why you wrote in your question that you feel it has something to do with that.
System.in does not represent the keyboard. It represents the java process's 'standard in' stream. If you just run java -jar foo.jar or whatnot on the command line (which is its own process, called the 'shell' - it'll be cmd.exe on windows, perhaps /bin/bash on linux. It's just an application, nothing special) - then that shell will decide that you intended to hook up the keyboard (technically, the 'terminal', which is usually virtualized, for example if you use ssh or other tools to remote your way onto another server, usually a physical keyboard isn't even connected to those things!).
But that's just because you started that process in a command line without explicitly specifying. If you double-click a jar on linux you probably won't get any terminal and nothing will be hooked up to standard in. If instead you start java -jar yourapp.jar <somefile.txt then bash will open the somefile.txt and set that up as the standard in.
The keyboard never runs out - you won't get a NoSuchElementException there.
But files run out. Given that you get this error when you 'upload' your application, clearly, something has been hooked up when whatever you uploaded it to runs your application that isn't the keyboard. It's probably a file, or at any rate, a limited stream.
You're asking for more tokens when there is nothing left to give.
Here's one obvious explanation:
This is homework or some coding exercise / coding competition.
You are uploading it to a grading server or competition testing server.
That server is (obviously - or you'd have to hire folks to type input data in over and over!) running your java app with the test data hooked up to System.in, and not an actual keyboard or even a virtualized one. Nobody is entering any keys to toss the test data at your app.
You have misunderstood the format of what the input is, so your application attempts to read more tokens than there actually are.
You can trivially reproduce this error yourself. First make a text file named 'test.txt', containing the string Hello and nothing more:
> cat test.txt
Hello
> cat Test.java
public class Test {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
System.out.println(in.next());
System.out.println(in.next());
}
}
> javac Test.java
> java Test <test.txt
NoSuchElementException
After all, this code tries to read 2 tokens from the standard input, which is that test file, which doesn't have 2 tokens. The same thing is happening in your setup.
SOLUTION: Reread the exercise description, you've misunderstood the inputs. For example, I bet the description says that a blank line means you need to exit the app, or if a command quit or exit comes in, or whatnot. Your app runs forever, it's highly unlikely homework / a coding exercise requires this.
My scenario:
I have a Main.java file that simply does System.out.println("Hello").
I run it by first, compiling with javac Main.java and then excecuting the command java Main.
Now what I want is that instead of printing "Hello", it will print whatever the user wants, but I don't want to change the source code whenever I want a different output. So I replaced the System.out.println("Hello") with System.out.println(${MESSAGE}). But this gives error "Cannot resolve symbol MESSAGE".
Ultimately, I want a Main.class file and run with something like java Main -env MESSAGE=whateverIPutHere and it should print out whateverIPutHere.
Is it possible?
You can use system properties
public final class Test {
public static void main(String[] args) {
System.out.println(System.getProperty("port") + " port");
}
}
And then compile and run
javac Test.java
java -Dport=8080 Test
Output is : 8080 port
Now what I want is that instead of printing "Hello", it will print whatever the user wants, but I don't want to change the source code.
Simply not possible without changing code.
System.out.println("Hello")
Prints that string. End of story. And:
System.out.println(${MESSAGE})
is simply not valid Java. If you want to read an environment variable, see here how to do that.
But then: that is really a detour here. You can simply pass arguments on the command line:
java Main "some string" "and another one"
and then retrieve those two strings via the String args[] parameter that your main method receives!
The real answer here: you learn a new language by researching how that language works. You don't assume how syntax might look like, based on experiences from other languages. Meaning: $ENV_VAR is a "shell language" concept. Your idea: "maybe Java has the same" is a very inefficient strategy to go about this.
You can use the input arguments:
public static void main(String[] args) {
System.out.println(args[0]);
}
And then call it like this: java Main whateverIPutHere
Simple as that! args is an array containing all the arguments that you pass in the command line.
In this example, we are printing all the arguments passed from the command-line. For this purpose, we have traversed the array using for loop. The arguments passed in command line is captured by args argument.
class test{
public static void main(String args[]){
for(int i=0;i<args.length;i++)
System.out.println(args[i]);
}
}
compile by > javac test.java
run by > java test sonoo jaiswal 1 3 abc
Output:
sonoo
jaiswal
1
3
abc
You can either read it from args as mentioned above, or, if you know how to add a library to your project, try args4j. You'll get way cleaner code as you can use it to separate commandline argument processing to a dedicated class.
so I'm new to using IntelliJ and I've tried googling but to no avail.
I'm creating a simple java program that basically prints hello and gets the user input (name) and prints it... Just to get the ball rolling. Normal Hello World prints fine..
But as soon as I add any [args] in it just crashes? Is there a way I can type the input in?
public class Main {
public static void main(String[] args) {
System.out.println("Hello, " + args[0] + "!");
}
}
You need to provide at least 1 argument if you access args[0] otherwise you get ArrayIndexOutOfBoundsException.
Why ? because the args[] is empty without any arguments passed so accessing the first one will throw the exception
How do you input commandline argument in IntelliJ IDEA?
There's an "edit configurations" item on the Run menu. In that panel, you can create a configuration and then you can choose the Class containing main().
add VM parameters and command-line args, specify the working directory and any environment variables.
you are done.
Sorry guys figured it out:
Go to Run
Edit Configurations > on the left side make sure you're in your Main class or whatever class you're using
Enter what you want in the program arguments. i.e. "James"
I was doing some work for college and my main runs this:
Spreadsheet sheet = new Spreadsheet(0,0);
SpreadsheetManager manager = new SpreadsheetManager(sheet);
/* Read an Import file, if any */
String filename = System.getProperty("import");
if (filename != null)
sheet.parseInputFile(filename, sheet);
Thing is, when I actually try to import a file it doesn't do what is supposed to and the filename is always null, so it never reaches my parseInputFile.
My teachers made a bunch of code for different programming exercises that do similar things available, and I've also looked at projects my colleagues did in previous years, but every single one does what I am doing above.
I have to run my program like this: java -Dimport=A-002-002-M-ok.import calc.textui.Calc otherwise none of the tests given by the teachers will run.
I'm sorry if this is not a useful question, but I've tried looking everywhere. If anyone could explain how the System.getProperty("import") works and why it isn't working in this case, I would be very grateful.
I suggest you take a look at the documentation of System.getProperty().
Basically it retrieves a value from the system, either already present or set by you.
To avoid retrieving null you can use another method signature that specify a default value:
System.getProperty("import", "file.txt");
To set a System property, you can specify it at launch:
java -Dimport="file.txt" your_application
or set it programatically :
System.setProperty("import", "file.txt");
When you run your program with:
java -Dimport=foo
then the method call
System.getProperty("import")
should return "foo".
Is ist possible that you write a tiny example program to convince yourself? Without any SheetManagers and all stuff, just
class ItWorks {
public static void main(String[] args) {
System.out.println(System.getProperty("import"));
}
}
Call it thus
java -Dimport=indeed ItWorks
and report what happens.
That being said: if you want to pass command line arguments, why don't you use the facility for command line arguments? (i.e. the String[] array passed to main?)
You could then call your program like this:
java calc.textui.Calc my-nice-spreadsheet.data
=====================================================
Please write the follwoing in your calc.textui.Calc program immediately after the open brace of your class definition:
public class Calc ..... { // a line like this already exists
// insert next line here
public static String filename = System.getProperty("import");
// rest of your class, as before.
}
Then comment out the getProperty() line in your method that didn't work, but leave the rest including the System.out.println(filename);
Does it change?
Maybe system properties are not the most indicated way to do that (depends on your application).
You could also use command line arguments to pass the file name to your main method:
public class CommandLineExample {
public static void main(String[] args) {
if (args.length < 1) {
System.err.println("usage: CommandLineExample <filename>");
System.exit(1);
}
String filename = args[0];
if (filename !=null && !filename.isEmpty()) {
...
}
}
}
Your program should be called as:
java CommandLineExample theFileName
the string "theFileName" will be passed to the main method in args[0] (any additional words will be passed in subsequent positions of args {args[1], args[2], ...})
EDIT
if the program must be called with
java -Dimport=filename ...
then System.getProperty("import") will return the filename.
Confirm that you are calling the correct program (class name, package, version, last compile was successful, ...) and also check that the property is not mistyped like java -Dinport=A-... or has additional spaces, uppercase letters...
In my ANJI (http://anji.sourceforge.net/) java project, I have two java file in package com.anji.neat.
One file names evolver.java which needs one program argument. The output champ-id from evolver.java is to be added as args[1] along with the previous argument fed to evolver.java
How can I add this output to Program Arguments without manually adding it? Plus is it possible that I execute these two java files in one run?
I know the question is complex, but someone kindlu help. I am new to java, so do not get things.
I would suggest that you have main method only in one file, lets say in evolver.java. Add a normal method in your second file which takes two arguments, first argument is the command line argument received in evlover.java and second argument is the champ-id. Run your program by calling the main method of evolver.java. Process the command line argument and generate the champ-id. And after that call the method of your second class by passing both the arguments.
It would become something "ugly" like:
public static void main(String[] args) {
if (args.length == 1) {
String extraArg;
...;
args = new Strinng[] { args[0], nextArg };
// main(args); return;
}
...
}