Java IO.pdf - Nguyen Dang Binh

Java I/O
The output buffer size is the number of bytes the driver can store for the output stream before
it can write to the port. This is important, because it's easy for a fast program to write data
faster than the port can send it out. Buffer overruns are a common problem, especially on
older PCs with slower serial ports.
Each of these properties has four methods: one enables the property, one disables it, one
checks whether the property is enabled, and one returns the current value. For instance, the
receive threshold is adjusted by these four methods:
public abstract void enableReceiveThreshold(int size)
throws UnsupportedCommOperationException
public abstract void disableReceiveThreshold()
public abstract boolean isReceiveThresholdEnabled()
public abstract int getReceiveThreshold()
The other three properties follow the same naming conventions. These four methods adjust
the receive time-out:
public abstract void enableReceiveTimeout(int rcvTimeout)
throws UnsupportedCommOperationException
public abstract void disableReceiveTimeout()
public abstract boolean isReceiveTimeoutEnabled()
public abstract int getReceiveTimeout()
These four methods adjust the receive framing property:
public abstract void enableReceiveFraming(int framingByte)
throws UnsupportedCommOperationException
public abstract void disableReceiveFraming()
public abstract boolean isReceiveFramingEnabled()
public abstract int getReceiveFramingByte()
These four methods adjust the input and output buffer sizes:
public abstract void setInputBufferSize(int size)
public abstract int getInputBufferSize()
public abstract void setOutputBufferSize(int size)
public abstract int getOutputBufferSize()
All drivers must support input and output buffers, so there are no isInputBufferEnabled()
or disableOutputBuffer() methods. However, other than the input and output buffer sizes,
drivers are not required to support these properties. If a driver does not support the given
property, then enabling it will throw an UnsupportedCommOperationException. You can
determine whether or not a driver supports a property by trying to enable it and seeing
whether or not an exception is thrown. Example 17.7 uses this scheme to test the properties
for the ports of the host system.
Example 17.7. PortTester
import javax.comm.*;
import java.util.*;
public class PortTester {
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