Java equivalent of stringstreams?

[jordan]

I am a longtime C++ programmer and I'm trying to understand how I would
phrase a common idiom in Java. Consider the following program in C++,
which reads tokens either from an istringstream (in memory) or from cin
(the console input):

#include <string>
#include <sstream>
#include <iostream>

using namespace std;

void readTokensFromStream(istream &in) {

string s;

while(in >> s) {
cout << "read from token: '" << s << "'" << endl;
}
}

int main() {

istringstream fromMem("a man a plan a canal panama");

readTokensFromStream(fromMem);

readTokensFromStream(cin);

return 0;
}

I'd like to be able to write something similar in Java, but it doesn't
appear so easy there. Whereas in C++, both istringstream and cin are
istreams, in Java you have StringReader (a reader, not a stream) and
System.in (an InputStream, not a reader). Is there a way to find a
common interface or adapter between the stream and reader/writer worlds
so that the program above can be elegantly stated in Java? My
definition of elegant would involve abstracting out the difference so
that readTokensFromStream could continue to be a single non-overloaded
method.

Thanks in advance.
Jordan

 

[John Harrison]

I am a longtime C++ programmer and I'm trying to understand how I would
phrase a common idiom in Java. Consider the following program in C++,
which reads tokens either from an istringstream (in memory) or from cin
(the console input):

#include <string>
#include <sstream>
#include <iostream>

using namespace std;

void readTokensFromStream(istream &in) {

string s;

while(in >> s) {
cout << "read from token: '" << s << "'" << endl;
}
}

int main() {

istringstream fromMem("a man a plan a canal panama");

readTokensFromStream(fromMem);

readTokensFromStream(cin);

return 0;
}

I'd like to be able to write something similar in Java, but it doesn't
appear so easy there. Whereas in C++, both istringstream and cin are
istreams, in Java you have StringReader (a reader, not a stream) and
System.in (an InputStream, not a reader). Is there a way to find a
common interface or adapter between the stream and reader/writer worlds
so that the program above can be elegantly stated in Java? My
definition of elegant would involve abstracting out the difference so
that readTokensFromStream could continue to be a single non-overloaded
method.

Thanks in advance.
Jordan

An InputStream is for reading bytes, a Reader is for reading characters.
A Reader must know about character set and encoding issues whereas an
InputStream doesn't need to worry.

You can use InputStreamReader to convert an InputStream to a Reader (and
you must explicitly or implicitly supply a CharSet when you do this).

Since your readTokensFromStream function is concerned with reading
character information it should take a Reader as a parameter.

john

 

[Roedy Green]

Is there a way to find a
common interface or adapter between the stream and reader/writer worlds
so that the program above can be elegantly stated in Java?

You use InputStreams for raw byte streams and Readers for streams of
encoded characters ( 8 or 16 bit ).

You can convert any InputStream to a Reader.

For sample code using the console as a Reader, see
http://mindprod.com/applets/fileio.html