I'm making a multi-player game where each player has their own input/output console on the screen. I'm having a bit of trouble trying to do this. I don't want every player to see other player's in/outputs.
To use an analogy, I want to do something like playerOneConsole.out.println("Player One String");, instead of System.out.println("Player One String"); where everyone can see player one's stuff.
After reading some documentation, I've tried this, but it does not work as intended as it throws a NullPointerException:
public class Player {
String myName;
Console myConsole;
public Player(String name) {
myName = name;
myConsole = System.console();
}
public void takeTurn(String playerOptions){
myConsole.writer().print(playerOptions); //This is not right.
}
}
I want playerOptions to print exclusively to that player's console, not the System console.
By the way, I'm using NetBeans IDE 8.0.2 if that makes a difference.
When using java.io.Console, you must execute the Java app from a console e.g. Windows CMD or Linux Terminal. Most IDEs won't execute Java through a console, so System#console returns null.
By the way, this code:
myConsole.writer().print(playerOptions); //This is not right.
It's right indeed :)
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.
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...
I am new to ExpectJ Java programming. I downloaded jar's and able to do few send() and expect() methods. send() would fire a command on console and expect() would identify any prompt's so inputs can be provided. Expect only reads is there are prompts, and not other info. For example, if want to fire, spawn.send("ls") and get list of all file names and so certain action, is that possible?.
Is there way so I can read normal output of spawn.send("ls") for example, without expect which only captures prompts?
You can indeed capture the output stream:
It is one of the methods of the ExpectJ.Spawn class
I am also very new to Java, but I got the output, however, I am still struggling on getting the prompt recognized as I get extra control characters from Unix so do not trust what comes after the second System.out.println (the sh,expect part)
the output works fine, just set it in a variable if you want, or if you use swing, send it to a textarea with a listener.
BTW! if you know how to do the expect without these bloody control characters, 1m,34 [001 and so on, I welcome your input
import expectj.ExpectJ;
import expectj.Spawn;
public class myExpectinator {
public myExpectinator(){
}
public void connect(){
try {
ExpectJ ex = new ExpectJ(10);
Spawn sh = ex.spawn("10.10.10.10", 22, "name", "password");
System.out.println(sh.getCurrentStandardOutContents());
System.out.println(sh.getCurrentStandardErrContents());
sh.expect("~ $");
sh.send("ps\n");
System.out.println(sh.getCurrentStandardOutContents());
//sh.expectClose();
sh.stop();
}
catch(Exception e) {
System.out.println(e);
}
}
}
I've made this little ATM application in Java (CLI) and in the beginning I want to have "Code: " and then the user should enter it, and in my Java application it should say something like String(or int?) code = 1234; and if that works then proceed, if not wrong, try again, if faulty 3 times, stop app.
How would something like that look? I've been googling for hours now after masked passwords and tried different types of code without any luck. I just want something simple that converts the string to asterisk.
Currently my password masking looks like this:
java.io.Console cons;
char[] passwd;
if ((cons = System.console()) != null && (passwd = cons.readPassword("[%s]", "Code:")) != null)
However I'm not able (don't know) how to set a password in the code.
Use the readPassword method of class java.io.Console.
The API documentation of class Console has an example that shows how to read a password from the console window without echoing it in plaintext.
edit
Michael, this code is to let a user enter a keyword in the console window without displaying it. After the user has done that, the password is stored in the variable passwd. It seems that what you really want is something completely different: you have some other program that asks for a password, and you want your program to enter that password automatically.
If that is indeed what you want to do, then you don't need to use class Console. You could try using class java.awt.Robot to enter keystrokes in another application (but I'm not sure that it would work with a console window - try it out).
This site has an example of pretty much exactly what you are trying to do: http://download.oracle.com/javase/tutorial/essential/io/cl.html
To be thorough, here are two more links to similar tutorials.
Do they answer your question?
Based on your comments, perhaps you do not understand Java syntax exactly.
You cannot write:
char["mypassword"] passwd;
I think you mean instead:
String str = "mypassword";
char[] passwd = str.toCharArray();
Update
Try this code:
Console c = System.console();
if (c == null) {
System.err.println("No console.");
System.exit(1);
}
char [] passwd = c.readPassword("Enter your password: ");
c.println("Password is:");
c.println(new String(passwd));
Take a look at this sun Java article... it highlights a number of different ways to do it.
Specifically it shows how to use AWT's TextField class with the setEchoChar() method, as well as a method that runs a separate thread to remove and replace typed characters in console applications.