Another IO Question

[ricky gonzalez]

Hi, another question....
Given the following code, under which circumstances will the method return false?
public static boolean test(InputStream is) throws IOException{
int value = is.read();
return value == (value & Oxff);
}
Select all valid answers.
a A character of more than 8 bits was read from the stream.
b An I/O error occurred.
c Never
d The end of the input was reached in the input stream.

[Amandeep Waraich]

I'm not sure..but the answer 'C' seems to be right...
Thanks,
Aman

[flora li]

at the end of file, value = -1.
-1 & oxff will be a positive value.
in this case value != value & ox11. the result will be false. so D is correct.

[mita]

Hi Dandan,
Could you please explain me how
-1 & oxff will be a positive value.
Thanks in advance.
mita

[Anonymous]

-1 = 1111 1111 1111 1111 1111 1111
0xff = 0000 0000 0000 0000 1111 1111
so -1 & 0xff will be
0000 0000 0000 0000 1111 1111 which is 255.

[mita]

Thank you Vasansrini.
mita

[Rahul Mahindrakar]

Lets checkout the options below
a A character of more than 8 bits was read from the stream.
// a programs should use the byte streams, descendants of InputStream and OutputStream, to read and write 8-bit bytes. Now since an InputStream was passed as parameter the program can read only 8 bit bytes as such this is wrong. Remember character streams (Reader and Writer) cannot be passed as parameters to methods that take InputStreams so this is false.
b An I/O error occurred.
// The read() method is declared as
public abstract int read()throws IOException.
Reads the next byte of data from the input stream. The value byte is returned as an int in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value -1 is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown. A subclass must provide an implementation of this method.
Returns : the next byte of data, or -1 if the end of the stream is reached.
Throws : IOException - if an I/O error occurs.
If an I/O exception occurs then the next statements ie (return value == (value & 0xFF) are not executed and the method returns terminating the program or exiting that particular block if the exception is handled. uncomment the lines in the program below and check out the results. this too does not return false.
c Never
// if all options are wrong maybe this one is correct
d The end of the input was reached in the input stream.
// correct. dandan and Vansrini have given appropriate answers for this. However check out the program below.

<font color="blue">
import java.io.*;
class  demo 
{static int value;
public static void main(String[] args) 
{
try{
File f=new File("autoexec.bat");
FileInputStream abc=new FileInputStream(f);

boolean b=true;
while (b)
{
b=test(abc);
}

System.out.println("The boolean value is "+b + " the value is " +value);
}
catch(Exception e){
System.out.println(e);
}

}
public static boolean test(InputStream is) throws IOException{
value = is.read();
//if (value==-1)
//{throw new IOException();
//}
return value == (value & 0xFF);
}
}
</font>

Regds.
Rahul.
[This message has been edited by Rahul Mahindrakar (edited August 04, 2000).]

[Anonymous]

The method returns an int while it needs to return a boolean, how can (d) be correct?

[Anonymous]

Ben,
return value == (value & 0xFF); does not return an int. It returns true if "value is equal to value & oxff"
It returns false otherwise.
true and false are boolean values.