public class DummyInputStream extends InputStream
System.inwill open such a
DummyInputStreamas a default. A user will later redirect
System.into a physically available device.
|Constructor and Description|
|Modifier and Type||Method and Description|
Returns an estimated number of bytes that can be read or skipped without blocking for more input.
Reads a single byte from this stream and returns it as an integer in the range from 0 to 255.
public int available()
Note that this method provides such a weak guarantee that it is not very useful in practice.
Firstly, the guarantee is "without blocking for more input" rather than "without blocking": a read may still block waiting for I/O to complete — the guarantee is merely that it won't have to wait indefinitely for data to be written. The result of this method should not be used as a license to do I/O on a thread that shouldn't be blocked.
Secondly, the result is a conservative estimate and may be significantly smaller than the actual number of bytes available. In particular, an implementation that always returns 0 would be correct. In general, callers should only use this method if they'd be satisfied with treating the result as a boolean yes or no answer to the question "is there definitely data ready?".
Thirdly, the fact that a given number of bytes is "available" does not guarantee that a read or skip will actually read or skip that many bytes: they may read or skip fewer.
It is particularly important to realize that you must not use this method to
size a container and assume that you can read the entirety of the stream without needing
to resize the container. Such callers should probably write everything they read to a
ByteArrayOutputStream and convert that to a byte array. Alternatively, if you're
reading from a file,
File.length() returns the current length of the file (though
assuming the file's length can't change may be incorrect, reading a file is inherently
The default implementation of this method in
InputStream always returns 0.
Subclasses should override this method if they are able to indicate the number of bytes
public int read()