I was using StringReader in a Data Structures assignment (Huffman codes), and was testing if the end of the string had been reached. I found that the int value that StringReader.read() returns is not -1, but 65535, so casting the result to a byte solved my infinite loop problem I was having.
Is this a bug in JDK, or is it common practice to cast values 开发者_JAVA百科returned from Reader.read() calls to bytes? Or am I missing something?
The gist of my code was something like this:
StringReader sr = new StringReader("This is a test string");
char c;
do {
c = sr.read();
//} while (c != -1); //<--Broken
} while ((byte)c != -1); //<--Works
In fact that doesn't even compile. I get:
Type mismatch: cannot convert from int to char
Since the sr.read()
call returns an int
I suggest you store it as such.
This compiles (and works as expected):
StringReader sr = new StringReader("This is a test string");
int i; // <-- changed from char
do {
i = sr.read();
// ... and if you need a char...
char c = (char) i;
} while (i != -1); // <-- works :-)
Why doesn't StringReader.Read() return a byte?
Strings are composed of 16-bit unicode characters. These won't fit in an 8-bit byte. One could argue that a char
would have been enough, but then there is no room for providing an indication that the EOF is reached.
Characters in java are 2 bytes because they're encoded in UTF-16. This is why read() returns an int, because byte is not large enough.
char c = (char) -1;
System.out.println(""+c);
System.out.println(""+(byte)c);
This code will solve your doubt ..
A Java String
is a sequence of chars
which are not bytes but values that represent UTF-16 code-points. The semantics of read
is to return the next atom from the input stream. In case of a StringReader
the atomic component is a 16-bit value which cannot be represented as a single byte.
StringReader#read
returns an int
value which is -1
if the end of the stream has been reached.
The problem in your code is that you already convert the int
value to a char and test the char:
System.out.println("Is it still (-1)?: " + (int) ((char) -1));
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