11 ms·

Which seems pretty amazing to me. Granted I'm not a Java developer, but it seems like such a basic feature of any language.

magpi3 13y ago
But how often do you read stdin in Java? It's a language that is used heavily to build web apps and (though less so) desktop GUI apps. I also programmed in Java for nearly a decade in the late nineties till about 2004 and have never used System.in for anything.
- Jtsummers 13y ago
  I'm writing desktop GUI apps in C# these days. Not the same as Java, but still many people would probably ask the same thing about C# as you've asked about Java: How often would you read stdin in C#? I use it at various prototyping stages of my applications. Oh, I need to handle a new file format. Ok, write the parser and classes to contain the file contents. Then create a quick console app that lets me read in a file and pose questions to it (give me the contents of data block 0x0840, what's its time tag, etc.). Now I need to run analyses on the file, and there's another file format that contains the queries. Create a quick console app that lets me combine those two pieces and a simple text interface to explore it. Then, once the pieces work, I plug them into the GUI. Now, do I do this every week? No, because after a certain point it's all about the GUI and other interactions. But it's a great way (for me) to prototype, and I'd use this approach regardless of the language for most programming tasks.
- cbsmith 13y ago
  > But how often do you read stdin in Java? Doesn't matter. For this problem it is just a conveniently available InputStream. How often do you read from an InputStream? I'd hope the answer to that isn't 0. > I also programmed in Java for nearly a decade in the late nineties till about 2004 and have never used System.in for anything. Okay, then change the problem to implementing this interface: public interface Copier { public void copy(java.io.InputStream in, java.io.PrintStream out); } That doesn't change the problem.
  - magpi3 13y ago
    Sure I am familiar with input streams, but we are talking about doing something from memory. One quick Google search leads to an "oh, of course that is what you would do" moment, but I am just noting that even in my Java hey day I would have needed that Google search before writing the requested code. Your interface does not change the problem, but it does phrase the problem in a more familiar way and would have been much more easy for me to respond to (in my Java hey day that is).
    - cbsmith 13y ago
      > Sure I am familiar with input streams, but we are talking about doing something from memory. It's an online quiz. You don't have to do it from memory.
jbooth 13y ago
It's definitely a basic feature of any language, including Java. I have no idea what the people upthread are talking about. From memory (may not compile) (edit thanks to cbsmith) import java.io.*; public static void main(String[] args) { byte[] buf = new byte[4096]; while (true) { int numRead = System.in.read(buf); if (numRead < 0) { // hit EOF, terminate System.out.flush(); System.exit(0); } System.out.write(buf,0,numRead); } }
- cbsmith 13y ago
  You need a test for the exit condition (read returning back -1) and you need to flush stdout.
  - jbooth 13y ago
    Right, thanks. Either way, it's not rocket surgery.
    - cbsmith 13y ago
      Agreed. Then again, you did mess it up the first time, so I guess it is an effective test. Everyone uses the buffer, which I find amusing.
- benkillin 13y ago
  just for the lolz, here is another way to do it without a buffer and using some java 8 features (lambdas) to avoid having to wrap the code in a try catch (technically you still are but it looks prettier IMHO): public class SimpleJavaTest { public interface RunnableEx { // can't use Callable<Void> because that run method needs to return a value public abstract void run() throws Exception; } public static void main(String[] args) { // write standard in to standard out: uncheck( () -> { int c; while( (c = System.in.read()) > -1) { System.out.write(c); } } ).run(); } public static Runnable uncheck(RunnableEx r) { return () -> { try { r.run(); } catch(Exception e) { throw new RuntimeException(e.getMessage(), e); } }; } }
mcherm 13y ago
And it IS a basic feature of Java. Just not one that is used much, and therefore not one that has a particularly clear or succinct idiom. Java didn't grow up in the world of unix where scripts that read from stdin and write to stdout get chained to produce pipelines. It grew up in the world of long-running stand-alone applications that communicate over sockets (like web applications). Java, because of the virtual machine, has a particularly slow start-up time and would be a poor choice for implementing mini pipeline components like this anyway.

magpi3 13y ago

But how often do you read stdin in Java? It's a language that is used heavily to build web apps and (though less so) desktop GUI apps. I also programmed in Java for nearly a decade in the late nineties till about 2004 and have never used System.in for anything.

Jtsummers 13y ago
I'm writing desktop GUI apps in C# these days. Not the same as Java, but still many people would probably ask the same thing about C# as you've asked about Java: How often would you read stdin in C#? I use it at various prototyping stages of my applications. Oh, I need to handle a new file format. Ok, write the parser and classes to contain the file contents. Then create a quick console app that lets me read in a file and pose questions to it (give me the contents of data block 0x0840, what's its time tag, etc.). Now I need to run analyses on the file, and there's another file format that contains the queries. Create a quick console app that lets me combine those two pieces and a simple text interface to explore it. Then, once the pieces work, I plug them into the GUI. Now, do I do this every week? No, because after a certain point it's all about the GUI and other interactions. But it's a great way (for me) to prototype, and I'd use this approach regardless of the language for most programming tasks.
cbsmith 13y ago
> But how often do you read stdin in Java? Doesn't matter. For this problem it is just a conveniently available InputStream. How often do you read from an InputStream? I'd hope the answer to that isn't 0. > I also programmed in Java for nearly a decade in the late nineties till about 2004 and have never used System.in for anything. Okay, then change the problem to implementing this interface: public interface Copier { public void copy(java.io.InputStream in, java.io.PrintStream out); } That doesn't change the problem.
- magpi3 13y ago
  Sure I am familiar with input streams, but we are talking about doing something from memory. One quick Google search leads to an "oh, of course that is what you would do" moment, but I am just noting that even in my Java hey day I would have needed that Google search before writing the requested code. Your interface does not change the problem, but it does phrase the problem in a more familiar way and would have been much more easy for me to respond to (in my Java hey day that is).
  - cbsmith 13y ago
    > Sure I am familiar with input streams, but we are talking about doing something from memory. It's an online quiz. You don't have to do it from memory.

jbooth 13y ago

It's definitely a basic feature of any language, including Java. I have no idea what the people upthread are talking about. From memory (may not compile) (edit thanks to cbsmith) import java.io.*; public static void main(String[] args) { byte[] buf = new byte[4096]; while (true) { int numRead = System.in.read(buf); if (numRead < 0) { // hit EOF, terminate System.out.flush(); System.exit(0); } System.out.write(buf,0,numRead); } }

cbsmith 13y ago
You need a test for the exit condition (read returning back -1) and you need to flush stdout.
- jbooth 13y ago
  Right, thanks. Either way, it's not rocket surgery.
  - cbsmith 13y ago
    Agreed. Then again, you did mess it up the first time, so I guess it is an effective test. Everyone uses the buffer, which I find amusing.
benkillin 13y ago
just for the lolz, here is another way to do it without a buffer and using some java 8 features (lambdas) to avoid having to wrap the code in a try catch (technically you still are but it looks prettier IMHO): public class SimpleJavaTest { public interface RunnableEx { // can't use Callable<Void> because that run method needs to return a value public abstract void run() throws Exception; } public static void main(String[] args) { // write standard in to standard out: uncheck( () -> { int c; while( (c = System.in.read()) > -1) { System.out.write(c); } } ).run(); } public static Runnable uncheck(RunnableEx r) { return () -> { try { r.run(); } catch(Exception e) { throw new RuntimeException(e.getMessage(), e); } }; } }

mcherm 13y ago

And it IS a basic feature of Java. Just not one that is used much, and therefore not one that has a particularly clear or succinct idiom. Java didn't grow up in the world of unix where scripts that read from stdin and write to stdout get chained to produce pipelines. It grew up in the world of long-running stand-alone applications that communicate over sockets (like web applications). Java, because of the virtual machine, has a particularly slow start-up time and would be a poor choice for implementing mini pipeline components like this anyway.