how to read input in java?

[abhilashm86]

so if we want read input from user,like i want to read integers from user,
alternate for scanf/raw_input in java??howto

public class jp3
{
public static void main(string args[])
{
int a,b,choice;

system.out.println("enter the any one of following choices\n");
system.out.println("1:add\n2:subtraction\n3:multiply\n");
..................

[fiddler616]

so if we want read input from user,like i want to read integers from user,
alternate for scanf/raw_input in java??howto

public class jp3
{
public static void main(string args[])
{
int a,b,choice;
Scanner scan = new Scanner(System.in);

system.out.println("enter the any one of following choices\n");
system.out.print("1:add\n2:subtraction\n3:multiply:");
int userInput = scan.nextInt();
..................
Read the API on the Scanner class in general (for String input and such)...

[apoth]

Old way:

http://www.particle.kth.se/~lindsey/JavaCourse/Book/Part1/Java/Chapter09/consoleTextIn.html

New way (version 6 onwards I think?):

http://www.java2s.com/Code/Java/Development-Class/UseScannertoreaduserinput.htm

[jimi_hendrix]

imo java fails at reading input :)

[abhilashm86]

public class jp3
{
public static void main (String args[])
{
int a,b,choice;
// Scanner scan=new Scanner(System.in);

System.out.println("enter the any one of following choices\n");
System.out.println("2:add\n2:subtraction\n3:multiply\n");

choice=System.in.read();

System.out.println(+choice);
}
}

so following error was given,

abhilash@abhi:~$ javac jp3.java
----------
1. ERROR in jp3.java (at line 11)
choice=System.in.read();
^^^^^^^^^^^^^^^^
Unhandled exception type IOException
----------
1 problem (1 error)

how to check version of java being currently used??
java -v din't work

[simeon87]

public static void main(String[] args) {
try {
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
String line = in.readLine();

System.out.println("You just entered: " + line);

} catch (IOException e) {
e.printStackTrace();
}
}

[jespdj]

imo java fails at reading input :)
What do you mean by this?

[cabalas]

imo java fails at reading input :)

+1 - The amount of cruft you have to add to read command line input in java is just crazy.

[jimi_hendrix]

What do you mean by this?

python: str = raw_input("input please");

C#: str = Console.ReadLine();

C++: cin.getline(str, 256);

C: str = gets(); /*depricated i know but i am too lazy to google the format for fgets*/

Erlang: str = io:get_line("input please");

java requires instantiation and other stuff...must i go on?

[fiddler616]

python: str = raw_input("input please");

C#: str = Console.ReadLine();

C++: cin.getline(str, 256);

C: str = gets(); /*depracated i know but i am too lazy to google the format for fgets*/

Erlang: str = io:get_line("input please");

java requires instantiation and other stuff...must i go on?
When I first learned about Scanner I had one of the biggest wtf moments of my programming life. Never mind about the difference between scan.next(), scan.nextLine(), scan.nextInt(), etc.
Python wins the prize, as usual, raw_input() gives you a string, and you can just wrap it up in an int() function (or _insert-datatype-here_ function) if you want something else.

[Tomosaur]

Input is my biggest annoyance with Java. Seriously, why does it have to be so damn stupid about it?

It's better to just emulate the C# way by creating a Console class like the example given by apoth, but it still requires way too much.

[fiddler616]

Input is my biggest annoyance with Java. Seriously, why does it have to be so damn stupid about it?

It's better to just emulate the C# way by creating a Console class like the example given by apoth, but it still requires way too much.
I also get pretty upset about applets...

[jimi_hendrix]

i am sorry linux world

C# > Java *ducks*

[fiddler616]

i am sorry linux world

C# > Java *ducks*
Java's more common though, as far as I know.
Also, the company that made it also made a ***ing RE for Linux (Mono's nice, but where's Microsoft Mono?)

[jimi_hendrix]

Java's more common though, as far as I know.
Also, the company that made it also made a ***ing RE for Linux (Mono's nice, but where's Microsoft Mono?)

when we become popular it will appear

and C# is growing fast...i just read a post on stackoverflow.com about it

[fiddler616]

when we become popular it will appear

and C# is growing fast...i just read a post on stackoverflow.com about it
I don't know...the less we rely on Microsoft software the better, as far as I'm concerned. I just spent a fun hour today figuring out why my Zune software would only play the first thirty seconds of a given track. Don't get me wrong, I like Zunes a lot, but the software tends to drive me bonkers.
*ducks, as slavik swoops in and closes thread for being OT*

[abhilashm86]

friends this topic is becoming a debate?? where is the solution?? i want a good book that has java from basics and number of programs?? can anyone tell, now i'm using head-first-java

[directhex]

friends this topic is becoming a debate?? where is the solution?? i want a good book that has java from basics and number of programs?? can anyone tell, now i'm using head-first-java

Try Deitel&Deitel. It worked for me when I was an undergrad

[jespdj]

python: str = raw_input("input please");

C#: str = Console.ReadLine();

C++: cin.getline(str, 256);

C: str = gets(); /*depricated i know but i am too lazy to google the format for fgets*/

Erlang: str = io:get_line("input please");

java requires instantiation and other stuff...must i go on?
So you say "Java fails at reading input" just because the syntax looks strange and unfamiliar to you? Hmmm... :rolleyes:

What about this method:
System.out.println("What's your name?");
String name = System.console().readLine();
I really don't see how this is much more complicated than those other languages that you quoted.

Input is my biggest annoyance with Java. Seriously, why does it have to be so damn stupid about it?
Because you didn't read the Java documentation or don't know how to use it?

It's better to just emulate the C# way by creating a Console class like the example given by apoth, but it still requires way too much.
Lookup the class java.io.Console in the Java SE 6 API documentation.

[abhilashm86]

What about this method:
System.out.println("What's your name?");
String name = System.console().readLine();


i just tried this and found following error,
public class jp2
{
public static void main (String[] args)
{
System.out.println("whts ur name?");
System.out.println("What's your name?");
String name = System.console().readLine();

}
}






abhilash@abhi:~$ javac jp2.java
----------
1. ERROR in jp2.java (at line 7)
String name = System.console().readLine();
^^^^^^^
The method console() is undefined for the type System
----------
1 problem (1 error)abhilash@abhi:~$

[Zugzwang]

1. ERROR in jp2.java (at line 7)
String name = System.console().readLine();
^^^^^^^
The method console() is undefined for the type System
----------
1 problem (1 error)


Did you made sure that you are using the Sun JDK with a version number >= 1.6?

[abhilashm86]

Did you made sure that you are using the Sun JDK with a version number >= 1.6?

i am using following java version, i had initially used eclipse for learning python but using vim editor to learn java, is it correct version?
if not tell how to change? please help

abhilash@abhi:~$ javac -v
Eclipse Java Compiler v_774_R33x, 3.3.1, Copyright IBM Corp 2000, 2007. All rights reserved.

[Tomosaur]

So you say "Java fails at reading input" just because the syntax looks strange and unfamiliar to you? Hmmm... :rolleyes:

What about this method:
System.out.println("What's your name?");
String name = System.console().readLine();I really don't see how this is much more complicated than those other languages that you quoted.


Because you didn't read the Java documentation or don't know how to use it?


Lookup the class java.io.Console in the Java SE 6 API documentation.

No, because this is ******* ugly: System.console().readLine(). Even using that, it is still better to wrap it up in a static method in a Console class so you can just use Console.readLine(). Just because Java now has a slightly less crappy way to read input does not make it 'good'.

[simeon87]

No, because this is ******* ugly: System.console().readLine(). Even using that, it is still better to wrap it up in a static method in a Console class so you can just use Console.readLine(). Just because Java now has a slightly less crappy way to read input does not make it 'good'.

I think you're overreacting here.. Java has simply chosen a different way of solving this than the one you would have preferred. In usage, the difference is minor anyway (ooh, a static method or a console() call in between).

[Tomosaur]

I think you're overreacting here.. Java has simply chosen a different way of solving this than the one you would have preferred. In usage, the difference is minor anyway (ooh, a static method or a console() call in between).

If you don't care about your software failing disastrously, then yes, the difference is minor. What jespdj neglected to mention is that to ensure we don't end up with errors and broken beaviour, reading from the console now actually requires the following:


Console cons = System.console();
string s;
if(cons != null){
s = cons.readLine();
}


And if System.console() DOES return null when you don't expect it to, what do you do? Why, you try to instantiate Console yourself and check for exceptions! Assuming the JVM will always successfully instantiate the console if it exists is just not an option for many developers, unfortunately.

The Java API designers need to look up 'simplification' in the dictionary, as far as I'm concened.

[howlingmadhowie]

i am sorry linux world

C# > Java *ducks*

that's a bit like saying friday the 13th part 5 has more intellectual depth than nightmare on elm street part 7.

[howlingmadhowie]

System.out.println("What's your name?");
String name = System.console().readLine();


does that actually work nowadays? i know it doesn't work in netbeans, not sure about eclipse.

[jimi_hendrix]

@Tomosaur

thank you

and if sun's ide (netbeas is suns right?) doesnt support it then something is fishy...

@howie

i fail to see the logic of calling either language a horror movie...java is well known and used and i find .Net genious (i wish it was open source :()

[howlingmadhowie]

i am using following java version, i had initially used eclipse for learning python but using vim editor to learn java, is it correct version?
if not tell how to change? please help

abhilash@abhi:~$ javac -v
Eclipse Java Compiler v_774_R33x, 3.3.1, Copyright IBM Corp 2000, 2007. All rights reserved.

you can check your jvm version by entering:


java -version

note the single minus sign. typical sun... #-o

[fiddler616]

java is well known and used
So are toilets. Does this make them elegant?

[jimi_hendrix]

So are toilets. Does this make them elegant?

solid 24k gold ones are

[fiddler616]

solid 24k gold ones are
...Python? :)
(Actually, that would be kind of tacky, seems like...)

[jespdj]

If you don't care about your software failing disastrously, then yes, the difference is minor. What jespdj neglected to mention is that to ensure we don't end up with errors and broken beaviour, reading from the console now actually requires the following: ...
So, what happens in C# / Python / some other language when you run the program without a console and you try to read user input from it? Will it magically work OK if the console is not there?

[jespdj]

abhilash@abhi:~$ javac -v
Eclipse Java Compiler v_774_R33x, 3.3.1, Copyright IBM Corp 2000, 2007. All rights reserved.
Really strange that you have the Eclipse Java compiler setup in such a way that you can call it from the command line like that.

Install the JDK for Sun Java 6:
sudo apt-get install sun-java6-jdk
Then, use this command to make Sun Java 6 the default version of Java that's used on your system:
sudo update-alternatives --config java
If necessary, remove the directory that contains the javac from Eclipse from your PATH.

[abhilashm86]

Really strange that you have the Eclipse Java compiler setup in such a way that you can call it from the command line like that.


hey i actually installed eclipse through scratch, so i also have sun java installed i think, check this out,


abhilash@abhi:~$ java -version
java version "1.6.0_0"
OpenJDK Runtime Environment (build 1.6.0_0-b11)
OpenJDK Client VM (build 1.6.0_0-b11, mixed mode, sharing)

so should i need to upgrade or how to make it default version in command line??
i don't want eclpise as default

[jespdj]

abhilash@abhi:~$ java -version
java version "1.6.0_0"
OpenJDK Runtime Environment (build 1.6.0_0-b11)
OpenJDK Client VM (build 1.6.0_0-b11, mixed mode, sharing)
That's OpenJDK Java, which is not exactly the same as Sun Java. It's almost the same, so using this is OK.

Did you try the update-alternatives command? What does your PATH look like; does it have a reference to a directory containing an Eclipse version of javac?
echo $PATH

[abhilashm86]

Did you try the update-alternatives command? What does your PATH look like; does it have a reference to a directory containing an Eclipse version of javac?


yea i tried updating, its not updating as its latest version,

abhilash@abhi:~$ sudo apt-get install sun-java6-jdk
Reading package lists... Done
Building dependency tree
Reading state information... Done
sun-java6-jdk is already the newest version.
The following packages were automatically installed and are no longer required:
linux-headers-2.6.24-22-generic linux-headers-2.6.24-22
Use 'apt-get autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 2 not upgraded.

so i guess using this jdk is not much difference to learn java,also

abhilash@abhi:~$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games

i don't know much about path, hey but i compiled two java programs with no errors and i hope everything is working right:)thanls

[Tomosaur]

So, what happens in C# / Python / some other language when you run the program without a console and you try to read user input from it? Will it magically work OK if the console is not there?

This:

try{
//read input
}
catch(Exception ex){
//deal with it
}


I'm willing to accept that Java has to do things differently because it runs on so many different platforms, but the fact that you have to check it twice is just stupid.

Anyway - as far as I can make out, the logic behind Java trying to get the console itself is this: 'You might need it'. I'd rather recognise when I need it and sort it out myself than have Java trying to be clever. It saves me no time or effort by forcing me to check for another point of failure.

[jimi_hendrix]

So, what happens in C# / Python / some other language when you run the program without a console and you try to read user input from it? Will it magically work OK if the console is not there?

what do you mean?
last time i tried this (a long long time ago) it opened a terminal...until the program ended

if you mean some other type of input please specify

[jespdj]

what do you mean?
last time i tried this (a long long time ago) it opened a terminal...until the program ended

if you mean some other type of input please specify
Tomosaur was complaining that if you run a Java program not from the console, System.console() returns null, and that you have to check if the console is really there or not, which makes the code a little bit longer than a single line System.console().readLine().

My response was that you'd have to so similar checking in other programming languages - so his argument that it's still more cumbersome in Java than in other programming languages is not valid.

[Tomosaur]

Tomosaur was complaining that if you run a Java program not from the console, System.console() returns null, and that you have to check if the console is really there or not, which makes the code a little bit longer than a single line System.console().readLine().

My response was that you'd have to so similar checking in other programming languages - so his argument that it's still more cumbersome in Java than in other programming languages is not valid.

Who said anything about running the program from console? That's not what I was saying at all. My point was that if I need to use the console, and I want my code to be safe, then I am forced to check the console twice if I'm using Java. System.console() could return null for any number of reasons - there are other things which could go wrong than the console simply not being there.

Sanity says I should be doing this:

try
{
//normal code including console input
}
catch(Exception)
{
//failure code
}
Whilst Java forces me to do this:
Java:

//You can put the if-else in the try-catch or whatever - the point is that you'll be doing both if you don't want your program to just fail miserably

Console c = System.console();
if(c != null)
{
//continue
}
else
{
try
{
//normal code including console input
}
catch(Exception)
{
//failure code
}
}
Obviously the Java code can look different - and that's precisely the problem. How do you do it in a way which means you've covered every eventuality? You have to check the console is not null - but where do you go from there? Since the JVM doesn't throw an exception, and I assume you don't just want your program to fail, you should check one more time since you haven't received an error. So you use a try-catch block (maybe). Oh but obviously you don't want to write the same code twice so you should probably put the actual console reading bit in a different method (and so on, and so on). This is absolutely ridiculous. Java has got it wrong here, plain and simple.

There is no standardised way to get console input because no matter what we do, we always have to check twice that we have received the console. The console should throw an exception if there's a problem, not just return null. It's all well and good that the JVM hides the error by just returning null - but until you receive an exception you don't know what the problem is. There's only so much hand holding the JVM can do before it starts causing its own problems (i.e this).

Exceptions should not be converted to return values for precisely this reason.

[jimi_hendrix]

Tomosaur was complaining that if you run a Java program not from the console, System.console() returns null, and that you have to check if the console is really there or not, which makes the code a little bit longer than a single line System.console().readLine().

My response was that you'd have to so similar checking in other programming languages - so his argument that it's still more cumbersome in Java than in other programming languages is not valid.

i just tried:


print 'hello world'


and ran from a file browser...not cli...generated a console...

i am not trying to be a troll, just trying to understand the statement of the console not being there...