Reader returns '?' instead of EOF

[David Kensche]

Hi,
I'm reading a String from a reader. When the string
is done the ready() method remains true and question
marks are read. So this snippet does not terminate:

reader = new PushbackReader(new StringReader(expression));
parsed = "";
StringExpression expr = new StringExpression(symbolTable);
char current;
while(reader.ready()) {
do {
current = (char)reader.read();
} while(current == ' ');
parsed += current;
if(current == '\'') {
expr.appendConstant(parseConstant());
} else if(current == '?') {
expr.appendVariable(parseVariableName());
}
}

Can anybody help?

Thanks beforehand,
David

 

[Chris Smith]

I'm reading a String from a reader. When the string
is done the ready() method remains true and question
marks are read.

David,

The ready() method doesn't do what you think it does. All the ready()
method does is check whether you can read from the Reader without
blocking. Since a StringReader will never block, ready() will most
likely always return true. Note that there's nothing in the
documentation for ready() that would indicate that it should return
false when you reach the end of stream. I don't know where you got that
expectation from.

The right way to detect end of stream is to watch for the return value
of the read() method to be -1.

--
www.designacourse.com
The Easiest Way to Train Anyone... Anywhere.

Chris Smith - Lead Software Developer/Technical Trainer
MindIQ Corporation

 

[Gordon Beaton]

I'm reading a String from a reader. When the string is done the
ready() method remains true and question marks are read. So this
snippet does not terminate:

That's the problem with using ready(). It hides EOF from you.

But there's no need to call ready() at all in your example. You can
simply call read() until it indicates that EOF has been reached:

int c;

while ((c = reader.read()) != -1) {
current = (char)c;
if (current == ' ') continue;

[ ... remaining lines... ]
}

/gordon