001: /*
002: * @(#)FileDescriptor.java 1.26 06/10/10
003: *
004: * Copyright 1990-2006 Sun Microsystems, Inc. All Rights Reserved.
005: * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER
006: *
007: * This program is free software; you can redistribute it and/or
008: * modify it under the terms of the GNU General Public License version
009: * 2 only, as published by the Free Software Foundation.
010: *
011: * This program is distributed in the hope that it will be useful, but
012: * WITHOUT ANY WARRANTY; without even the implied warranty of
013: * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
014: * General Public License version 2 for more details (a copy is
015: * included at /legal/license.txt).
016: *
017: * You should have received a copy of the GNU General Public License
018: * version 2 along with this work; if not, write to the Free Software
019: * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
020: * 02110-1301 USA
021: *
022: * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa
023: * Clara, CA 95054 or visit www.sun.com if you need additional
024: * information or have any questions.
025: *
026: */
027:
028: package java.io;
029:
030: /**
031: * Instances of the file descriptor class serve as an opaque handle
032: * to the underlying machine-specific structure representing an open
033: * file, an open socket, or another source or sink of bytes. The
034: * main practical use for a file descriptor is to create a
035: * <code>FileInputStream</code> or <code>FileOutputStream</code> to
036: * contain it.
037: * <p>
038: * Applications should not create their own file descriptors.
039: *
040: * @version 1.18, 02/02/00
041: * @see java.io.FileInputStream
042: * @see java.io.FileOutputStream
043: * @since JDK1.0
044: */
045: public final class FileDescriptor {
046:
047: private int fd;
048:
049: /**
050: * Constructs an (invalid) FileDescriptor
051: * object.
052: */
053: public/**/FileDescriptor() {
054: fd = -1;
055: }
056:
057: private/* */FileDescriptor(int fd) {
058: this .fd = fd;
059: }
060:
061: /**
062: * A handle to the standard input stream. Usually, this file
063: * descriptor is not used directly, but rather via the input stream
064: * known as <code>System.in</code>.
065: *
066: * @see java.lang.System#in
067: */
068: public static final FileDescriptor in = new FileDescriptor(0);
069:
070: /**
071: * A handle to the standard output stream. Usually, this file
072: * descriptor is not used directly, but rather via the output stream
073: * known as <code>System.out</code>.
074: * @see java.lang.System#out
075: */
076: public static final FileDescriptor out = new FileDescriptor(1);
077:
078: /**
079: * A handle to the standard error stream. Usually, this file
080: * descriptor is not used directly, but rather via the output stream
081: * known as <code>System.err</code>.
082: *
083: * @see java.lang.System#err
084: */
085: public static final FileDescriptor err = new FileDescriptor(2);
086:
087: /**
088: * Tests if this file descriptor object is valid.
089: *
090: * @return <code>true</code> if the file descriptor object represents a
091: * valid, open file, socket, or other active I/O connection;
092: * <code>false</code> otherwise.
093: */
094: public boolean valid() {
095: return fd != -1;
096: }
097:
098: /**
099: * Force all system buffers to synchronize with the underlying
100: * device. This method returns after all modified data and
101: * attributes of this FileDescriptor have been written to the
102: * relevant device(s). In particular, if this FileDescriptor
103: * refers to a physical storage medium, such as a file in a file
104: * system, sync will not return until all in-memory modified copies
105: * of buffers associated with this FileDesecriptor have been
106: * written to the physical medium.
107: *
108: * sync is meant to be used by code that requires physical
109: * storage (such as a file) to be in a known state For
110: * example, a class that provided a simple transaction facility
111: * might use sync to ensure that all changes to a file caused
112: * by a given transaction were recorded on a storage medium.
113: *
114: * sync only affects buffers downstream of this FileDescriptor. If
115: * any in-memory buffering is being done by the application (for
116: * example, by a BufferedOutputStream object), those buffers must
117: * be flushed into the FileDescriptor (for example, by invoking
118: * OutputStream.flush) before that data will be affected by sync.
119: *
120: * @exception SyncFailedException
121: * Thrown when the buffers cannot be flushed,
122: * or because the system cannot guarantee that all the
123: * buffers have been synchronized with physical media.
124: * @since JDK1.1
125: */
126: public native void sync() throws SyncFailedException;
127:
128: /* This routine initializes JNI field offsets for the class */
129: private static native void initIDs();
130:
131: static {
132: initIDs();
133: }
134: }
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