关于RunTime类的介绍：
1 /**
2 * Every Java application has a single instance of class
3 * <code>Runtime</code> that allows the application to interface with
4 * the environment in which the application is running. The current
5 * runtime can be obtained from the <code>getRuntime</code> method.
6 * <p>
7 * An application cannot create its own instance of this class.
8 *
9 * @author unascribed
10 * @see java.lang.Runtime#getRuntime()
11 * @since JDK1.0
12 */
13
14 public class Runtime {
15 ......
16 }
RunTime类
类具体的定义：
1 public class Runtime {
2 private static Runtime currentRuntime = new Runtime();
3
4 /**
5 * Returns the runtime object associated with the current Java application.
6 * Most of the methods of class <code>Runtime</code> are instance
7 * methods and must be invoked with respect to the current runtime object.
8 *
9 * @return the <code>Runtime</code> object associated with the current
10 * Java application.
11 */
12 public static Runtime getRuntime() {
13 return currentRuntime;
14 }
15
16 /** Don‘t let anyone else instantiate this class */
17 private Runtime() {}
18
19 /**
20 * Terminates the currently running Java virtual machine by initiating its
21 * shutdown sequence. This method never returns normally. The argument
22 * serves as a status code; by convention, a nonzero status code indicates
23 * abnormal termination.
24 *
25 * <p> The virtual machine‘s shutdown sequence consists of two phases. In
26 * the first phase all registered {@link #addShutdownHook shutdown hooks},
27 * if any, are started in some unspecified order and allowed to run
28 * concurrently until they finish. In the second phase all uninvoked
29 * finalizers are run if {@link #runFinalizersOnExit finalization-on-exit}
30 * has been enabled. Once this is done the virtual machine {@link #halt
31 * halts}.
32 *
33 * <p> If this method is invoked after the virtual machine has begun its
34 * shutdown sequence then if shutdown hooks are being run this method will
35 * block indefinitely. If shutdown hooks have already been run and on-exit
36 * finalization has been enabled then this method halts the virtual machine
37 * with the given status code if the status is nonzero; otherwise, it
38 * blocks indefinitely.
39 *
40 * <p> The <tt>{@link System#exit(int) System.exit}</tt> method is the
41 * conventional and convenient means of invoking this method. <p>
42 *
43 * @param status
44 * Termination status. By convention, a nonzero status code
45 * indicates abnormal termination.
46 *
47 * @throws SecurityException
48 * If a security manager is present and its <tt>{@link
49 * SecurityManager#checkExit checkExit}</tt> method does not permit
50 * exiting with the specified status
51 *
52 * @see java.lang.SecurityException
53 * @see java.lang.SecurityManager#checkExit(int)
54 * @see #addShutdownHook
55 * @see #removeShutdownHook
56 * @see #runFinalizersOnExit
57 * @see #halt(int)
58 */
59 public void exit(int status) {
60 SecurityManager security = System.getSecurityManager();
61 if (security != null) {
62 security.checkExit(status);
63 }
64 Shutdown.exit(status);
65 }
66
67 /**
68 * Registers a new virtual-machine shutdown hook.
69 *
70 * <p> The Java virtual machine <i>shuts down</i> in response to two kinds
71 * of events:
72 *
73 * <ul>
74 *
75 * <li> The program <i>exits</i> normally, when the last non-daemon
76 * thread exits or when the <tt>{@link #exit exit}</tt> (equivalently,
77 * {@link System#exit(int) System.exit}) method is invoked, or
78 *
79 * <li> The virtual machine is <i>terminated</i> in response to a
80 * user interrupt, such as typing <tt>^C</tt>, or a system-wide event,
81 * such as user logoff or system shutdown.
82 *
83 * </ul>
84 *
85 * <p> A <i>shutdown hook</i> is simply an initialized but unstarted
86 * thread. When the virtual machine begins its shutdown sequence it will
87 * start all registered shutdown hooks in some unspecified order and let
88 * them run concurrently. When all the hooks have finished it will then
89 * run all uninvoked finalizers if finalization-on-exit has been enabled.
90 * Finally, the virtual machine will halt. Note that daemon threads will
91 * continue to run during the shutdown sequence, as will non-daemon threads
92 * if shutdown was initiated by invoking the <tt>{@link #exit exit}</tt>
93 * method.
94 *
95 * <p> Once the shutdown sequence has begun it can be stopped only by
96 * invoking the <tt>{@link #halt halt}</tt> method, which forcibly
97 * terminates the virtual machine.
98 *
99 * <p> Once the shutdown sequence has begun it is impossible to register a
100 * new shutdown hook or de-register a previously-registered hook.
101 * Attempting either of these operations will cause an
102 * <tt>{@link IllegalStateException}</tt> to be thrown.
103 *
104 * <p> Shutdown hooks run at a delicate time in the life cycle of a virtual
105 * machine and should therefore be coded defensively. They should, in
106 * particular, be written to be thread-safe and to avoid deadlocks insofar
107 * as possible. They should also not rely blindly upon services that may
108 * have registered their own shutdown hooks and therefore may themselves in
109 * the process of shutting down. Attempts to use other thread-based
110 * services such as the AWT event-dispatch thread, for example, may lead to
111 * deadlocks.
112 *
113 * <p> Shutdown hooks should also finish their work quickly. When a
114 * program invokes <tt>{@link #exit exit}</tt> the expectation is
115 * that the virtual machine will promptly shut down and exit. When the
116 * virtual machine is terminated due to user logoff or system shutdown the
117 * underlying operating system may only allow a fixed amount of time in
118 * which to shut down and exit. It is therefore inadvisable to attempt any
119 * user interaction or to perform a long-running computation in a shutdown
120 * hook.
121 *
122 * <p> Uncaught exceptions are handled in shutdown hooks just as in any
123 * other thread, by invoking the <tt>{@link ThreadGroup#uncaughtException
124 * uncaughtException}</tt> method of the thread‘s <tt>{@link
125 * ThreadGroup}</tt> object. The default implementation of this method
126 * prints the exception‘s stack trace to <tt>{@link System#err}</tt> and
127 * terminates the thread; it does not cause the virtual machine to exit or
128 * halt.
129 *
130 * <p> In rare circumstances the virtual machine may <i>abort</i>, that is,
131 * stop running without shutting down cleanly. This occurs when the
132 * virtual machine is terminated externally, for example with the
133 * <tt>SIGKILL</tt> signal on Unix or the <tt>TerminateProcess</tt> call on
134 * Microsoft Windows. The virtual machine may also abort if a native
135 * method goes awry by, for example, corrupting internal data structures or
136 * attempting to access nonexistent memory. If the virtual machine aborts
137 * then no guarantee can be made about whether or not any shutdown hooks
138 * will be run. <p>
139 *
140 * @param hook
141 * An initialized but unstarted <tt>{@link Thread}</tt> object
142 *
143 * @throws IllegalArgumentException
144 * If the specified hook has already been registered,
145 * or if it can be determined that the hook is already running or
146 * has already been run
147 *
148 * @throws IllegalStateException
149 * If the virtual machine is already in the process
150 * of shutting down
151 *
152 * @throws SecurityException
153 * If a security manager is present and it denies
154 * <tt>{@link RuntimePermission}("shutdownHooks")</tt>
155 *
156 * @see #removeShutdownHook
157 * @see #halt(int)
158 * @see #exit(int)
159 * @since 1.3
160 */
161 public void addShutdownHook(Thread hook) {
162 SecurityManager sm = System.getSecurityManager();
163 if (sm != null) {
164 sm.checkPermission(new RuntimePermission("shutdownHooks"));
165 }
166 ApplicationShutdownHooks.add(hook);
167 }
168
169 /**
170 * De-registers a previously-registered virtual-machine shutdown hook. <p>
171 *
172 * @param hook the hook to remove
173 * @return <tt>true</tt> if the specified hook had previously been
174 * registered and was successfully de-registered, <tt>false</tt>
175 * otherwise.
176 *
177 * @throws IllegalStateException
178 * If the virtual machine is already in the process of shutting
179 * down
180 *
181 * @throws SecurityException
182 * If a security manager is present and it denies
183 * <tt>{@link RuntimePermission}("shutdownHooks")</tt>
184 *
185 * @see #addShutdownHook
186 * @see #exit(int)
187 * @since 1.3
188 */
189 public boolean removeShutdownHook(Thread hook) {
190 SecurityManager sm = System.getSecurityManager();
191 if (sm != null) {
192 sm.checkPermission(new RuntimePermission("shutdownHooks"));
193 }
194 return ApplicationShutdownHooks.remove(hook);
195 }
196
197 /**
198 * Forcibly terminates the currently running Java virtual machine. This
199 * method never returns normally.
200 *
201 * <p> This method should be used with extreme caution. Unlike the
202 * <tt>{@link #exit exit}</tt> method, this method does not cause shutdown
203 * hooks to be started and does not run uninvoked finalizers if
204 * finalization-on-exit has been enabled. If the shutdown sequence has
205 * already been initiated then this method does not wait for any running
206 * shutdown hooks or finalizers to finish their work. <p>
207 *
208 * @param status
209 * Termination status. By convention, a nonzero status code
210 * indicates abnormal termination. If the <tt>{@link Runtime#exit
211 * exit}</tt> (equivalently, <tt>{@link System#exit(int)
212 * System.exit}</tt>) method has already been invoked then this
213 * status code will override the status code passed to that method.
214 *
215 * @throws SecurityException
216 * If a security manager is present and its <tt>{@link
217 * SecurityManager#checkExit checkExit}</tt> method does not permit
218 * an exit with the specified status
219 *
220 * @see #exit
221 * @see #addShutdownHook
222 * @see #removeShutdownHook
223 * @since 1.3
224 */
225 public void halt(int status) {
226 SecurityManager sm = System.getSecurityManager();
227 if (sm != null) {
228 sm.checkExit(status);
229 }
230 Shutdown.halt(status);
231 }
232
233 /**
234 * Enable or disable finalization on exit; doing so specifies that the
235 * finalizers of all objects that have finalizers that have not yet been
236 * automatically invoked are to be run before the Java runtime exits.
237 * By default, finalization on exit is disabled.
238 *
239 * <p>If there is a security manager,
240 * its <code>checkExit</code> method is first called
241 * with 0 as its argument to ensure the exit is allowed.
242 * This could result in a SecurityException.
243 *
244 * @param value true to enable finalization on exit, false to disable
245 * @deprecated This method is inherently unsafe. It may result in
246 * finalizers being called on live objects while other threads are
247 * concurrently manipulating those objects, resulting in erratic
248 * behavior or deadlock.
249 *
250 * @throws SecurityException
251 * if a security manager exists and its <code>checkExit</code>
252 * method doesn‘t allow the exit.
253 *
254 * @see java.lang.Runtime#exit(int)
255 * @see java.lang.Runtime#gc()
256 * @see java.lang.SecurityManager#checkExit(int)
257 * @since JDK1.1
258 */
259 @Deprecated
260 public static void runFinalizersOnExit(boolean value) {
261 SecurityManager security = System.getSecurityManager();
262 if (security != null) {
263 try {
264 security.checkExit(0);
265 } catch (SecurityException e) {
266 throw new SecurityException("runFinalizersOnExit");
267 }
268 }
269 Shutdown.setRunFinalizersOnExit(value);
270 }
271
272 /**
273 * Executes the specified string command in a separate process.
274 *
275 * <p>This is a convenience method. An invocation of the form
276 * <tt>exec(command)</tt>
277 * behaves in exactly the same way as the invocation
278 * <tt>{@link #exec(String, String[], File) exec}(command, null, null)</tt>.
279 *
280 * @param command a specified system command.
281 *
282 * @return A new {@link Process} object for managing the subprocess
283 *
284 * @throws SecurityException
285 * If a security manager exists and its
286 * {@link SecurityManager#checkExec checkExec}
287 * method doesn‘t allow creation of the subprocess
288 *
289 * @throws IOException
290 * If an I/O error occurs
291 *
292 * @throws NullPointerException
293 * If <code>command</code> is <code>null</code>
294 *
295 * @throws IllegalArgumentException
296 * If <code>command</code> is empty
297 *
298 * @see #exec(String[], String[], File)
299 * @see ProcessBuilder
300 */
301 public Process exec(String command) throws IOException {
302 return exec(command, null, null);
303 }
304
305 /**
306 * Executes the specified string command in a separate process with the
307 * specified environment.
308 *
309 * <p>This is a convenience method. An invocation of the form
310 * <tt>exec(command, envp)</tt>
311 * behaves in exactly the same way as the invocation
312 * <tt>{@link #exec(String, String[], File) exec}(command, envp, null)</tt>.
313 *
314 * @param command a specified system command.
315 *
316 * @param envp array of strings, each element of which
317 * has environment variable settings in the format
318 * <i>name</i>=<i>value</i>, or
319 * <tt>null</tt> if the subprocess should inherit
320 * the environment of the current process.
321 *
322 * @return A new {@link Process} object for managing the subprocess
323 *
324 * @throws SecurityException
325 * If a security manager exists and its
326 * {@link SecurityManager#checkExec checkExec}
327 * method doesn‘t allow creation of the subprocess
328 *
329 * @throws IOException
330 * If an I/O error occurs
331 *
332 * @throws NullPointerException
333 * If <code>command</code> is <code>null</code>,
334 * or one of the elements of <code>envp</code> is <code>null</code>
335 *
336 * @throws IllegalArgumentException
337 * If <code>command</code> is empty
338 *
339 * @see #exec(String[], String[], File)
340 * @see ProcessBuilder
341 */
342 public Process exec(String command, String[] envp) throws IOException {
343 return exec(command, envp, null);
344 }
345
346 /**
347 * Executes the specified string command in a separate process with the
348 * specified environment and working directory.
349 *
350 * <p>This is a convenience method. An invocation of the form
351 * <tt>exec(command, envp, dir)</tt>
352 * behaves in exactly the same way as the invocation
353 * <tt>{@link #exec(String[], String[], File) exec}(cmdarray, envp, dir)</tt>,
354 * where <code>cmdarray</code> is an array of all the tokens in
355 * <code>command</code>.
356 *
357 * <p>More precisely, the <code>command</code> string is broken
358 * into tokens using a {@link StringTokenizer} created by the call
359 * <code>new {@link StringTokenizer}(command)</code> with no
360 * further modification of the character categories. The tokens
361 * produced by the tokenizer are then placed in the new string
362 * array <code>cmdarray</code>, in the same order.
363 *
364 * @param command a specified system command.
365 *
366 * @param envp array of strings, each element of which
367 * has environment variable settings in the format
368 * <i>name</i>=<i>value</i>, or
369 * <tt>null</tt> if the subprocess should inherit
370 * the environment of the current process.
371 *
372 * @param dir the working directory of the subprocess, or
373 * <tt>null</tt> if the subprocess should inherit
374 * the working directory of the current process.
375 *
376 * @return A new {@link Process} object for managing the subprocess
377 *
378 * @throws SecurityException
379 * If a security manager exists and its
380 * {@link SecurityManager#checkExec checkExec}
381 * method doesn‘t allow creation of the subprocess
382 *
383 * @throws IOException
384 * If an I/O error occurs
385 *
386 * @throws NullPointerException
387 * If <code>command</code> is <code>null</code>,
388 * or one of the elements of <code>envp</code> is <code>null</code>
389 *
390 * @throws IllegalArgumentException
391 * If <code>command</code> is empty
392 *
393 * @see ProcessBuilder
394 * @since 1.3
395 */
396 public Process exec(String command, String[] envp, File dir)
397 throws IOException {
398 if (command.length() == 0)
399 throw new IllegalArgumentException("Empty command");
400
401 StringTokenizer st = new StringTokenizer(command);
402 String[] cmdarray = new String[st.countTokens()];
403 for (int i = 0; st.hasMoreTokens(); i++)
404 cmdarray[i] = st.nextToken();
405 return exec(cmdarray, envp, dir);
406 }
407
408 /**
409 * Executes the specified command and arguments in a separate process.
410 *
411 * <p>This is a convenience method. An invocation of the form
412 * <tt>exec(cmdarray)</tt>
413 * behaves in exactly the same way as the invocation
414 * <tt>{@link #exec(String[], String[], File) exec}(cmdarray, null, null)</tt>.
415 *
416 * @param cmdarray array containing the command to call and
417 * its arguments.
418 *
419 * @return A new {@link Process} object for managing the subprocess
420 *
421 * @throws SecurityException
422 * If a security manager exists and its
423 * {@link SecurityManager#checkExec checkExec}
424 * method doesn‘t allow creation of the subprocess
425 *
426 * @throws IOException
427 * If an I/O error occurs
428 *
429 * @throws NullPointerException
430 * If <code>cmdarray</code> is <code>null</code>,
431 * or one of the elements of <code>cmdarray</code> is <code>null</code>
432 *
433 * @throws IndexOutOfBoundsException
434 * If <code>cmdarray</code> is an empty array
435 * (has length <code>0</code>)
436 *
437 * @see ProcessBuilder
438 */
439 public Process exec(String cmdarray[]) throws IOException {
440 return exec(cmdarray, null, null);
441 }
442
443 /**
444 * Executes the specified command and arguments in a separate process
445 * with the specified environment.
446 *
447 * <p>This is a convenience method. An invocation of the form
448 * <tt>exec(cmdarray, envp)</tt>
449 * behaves in exactly the same way as the invocation
450 * <tt>{@link #exec(String[], String[], File) exec}(cmdarray, envp, null)</tt>.
451 *
452 * @param cmdarray array containing the command to call and
453 * its arguments.
454 *
455 * @param envp array of strings, each element of which
456 * has environment variable settings in the format
457 * <i>name</i>=<i>value</i>, or
458 * <tt>null</tt> if the subprocess should inherit
459 * the environment of the current process.
460 *
461 * @return A new {@link Process} object for managing the subprocess
462 *
463 * @throws SecurityException
464 * If a security manager exists and its
465 * {@link SecurityManager#checkExec checkExec}
466 * method doesn‘t allow creation of the subprocess
467 *
468 * @throws IOException
469 * If an I/O error occurs
470 *
471 * @throws NullPointerException
472 * If <code>cmdarray</code> is <code>null</code>,
473 * or one of the elements of <code>cmdarray</code> is <code>null</code>,
474 * or one of the elements of <code>envp</code> is <code>null</code>
475 *
476 * @throws IndexOutOfBoundsException
477 * If <code>cmdarray</code> is an empty array
478 * (has length <code>0</code>)
479 *
480 * @see ProcessBuilder
481 */
482 public Process exec(String[] cmdarray, String[] envp) throws IOException {
483 return exec(cmdarray, envp, null);
484 }
485
486
487 /**
488 * Executes the specified command and arguments in a separate process with
489 * the specified environment and working directory.
490 *
491 * <p>Given an array of strings <code>cmdarray</code>, representing the
492 * tokens of a command line, and an array of strings <code>envp</code>,
493 * representing "environment" variable settings, this method creates
494 * a new process in which to execute the specified command.
495 *
496 * <p>This method checks that <code>cmdarray</code> is a valid operating
497 * system command. Which commands are valid is system-dependent,
498 * but at the very least the command must be a non-empty list of
499 * non-null strings.
500 *
501 * <p>If <tt>envp</tt> is <tt>null</tt>, the subprocess inherits the
502 * environment settings of the current process.
503 *
504 * <p>A minimal set of system dependent environment variables may
505 * be required to start a process on some operating systems.
506 * As a result, the subprocess may inherit additional environment variable
507 * settings beyond those in the specified environment.
508 *
509 * <p>{@link ProcessBuilder#start()} is now the preferred way to
510 * start a process with a modified environment.
511 *
512 * <p>The working directory of the new subprocess is specified by <tt>dir</tt>.
513 * If <tt>dir</tt> is <tt>null</tt>, the subprocess inherits the
514 * current working directory of the current process.
515 *
516 * <p>If a security manager exists, its
517 * {@link SecurityManager#checkExec checkExec}
518 * method is invoked with the first component of the array
519 * <code>cmdarray</code> as its argument. This may result in a
520 * {@link SecurityException} being thrown.
521 *
522 * <p>Starting an operating system process is highly system-dependent.
523 * Among the many things that can go wrong are:
524 * <ul>
525 * <li>The operating system program file was not found.
526 * <li>Access to the program file was denied.
527 * <li>The working directory does not exist.
528 * </ul>
529 *
530 * <p>In such cases an exception will be thrown. The exact nature
531 * of the exception is system-dependent, but it will always be a
532 * subclass of {@link IOException}.
533 *
534 *
535 * @param cmdarray array containing the command to call and
536 * its arguments.
537 *
538 * @param envp array of strings, each element of which
539 * has environment variable settings in the format
540 * <i>name</i>=<i>value</i>, or
541 * <tt>null</tt> if the subprocess should inherit
542 * the environment of the current process.
543 *
544 * @param dir the working directory of the subprocess, or
545 * <tt>null</tt> if the subprocess should inherit
546 * the working directory of the current process.
547 *
548 * @return A new {@link Process} object for managing the subprocess
549 *
550 * @throws SecurityException
551 * If a security manager exists and its
552 * {@link SecurityManager#checkExec checkExec}
553 * method doesn‘t allow creation of the subprocess
554 *
555 * @throws IOException
556 * If an I/O error occurs
557 *
558 * @throws NullPointerException
559 * If <code>cmdarray</code> is <code>null</code>,
560 * or one of the elements of <code>cmdarray</code> is <code>null</code>,
561 * or one of the elements of <code>envp</code> is <code>null</code>
562 *
563 * @throws IndexOutOfBoundsException
564 * If <code>cmdarray</code> is an empty array
565 * (has length <code>0</code>)
566 *
567 * @see ProcessBuilder
568 * @since 1.3
569 */
570 public Process exec(String[] cmdarray, String[] envp, File dir)
571 throws IOException {
572 return new ProcessBuilder(cmdarray)
573 .environment(envp)
574 .directory(dir)
575 .start();
576 }
577
578 /**
579 * Returns the number of processors available to the Java virtual machine.
580 *
581 * <p> This value may change during a particular invocation of the virtual
582 * machine. Applications that are sensitive to the number of available
583 * processors should therefore occasionally poll this property and adjust
584 * their resource usage appropriately. </p>
585 *
586 * @return the maximum number of processors available to the virtual
587 * machine; never smaller than one
588 * @since 1.4
589 */
590 public native int availableProcessors();
591
592 /**
593 * Returns the amount of free memory in the Java Virtual Machine.
594 * Calling the
595 * <code>gc</code> method may result in increasing the value returned
596 * by <code>freeMemory.</code>
597 *
598 * @return an approximation to the total amount of memory currently
599 * available for future allocated objects, measured in bytes.
600 */
601 public native long freeMemory();
602
603 /**
604 * Returns the total amount of memory in the Java virtual machine.
605 * The value returned by this method may vary over time, depending on
606 * the host environment.
607 * <p>
608 * Note that the amount of memory required to hold an object of any
609 * given type may be implementation-dependent.
610 *
611 * @return the total amount of memory currently available for current
612 * and future objects, measured in bytes.
613 */
614 public native long totalMemory();
615
616 /**
617 * Returns the maximum amount of memory that the Java virtual machine will
618 * attempt to use. If there is no inherent limit then the value {@link
619 * java.lang.Long#MAX_VALUE} will be returned.
620 *
621 * @return the maximum amount of memory that the virtual machine will
622 * attempt to use, measured in bytes
623 * @since 1.4
624 */
625 public native long maxMemory();
626
627 /**
628 * Runs the garbage collector.
629 * Calling this method suggests that the Java virtual machine expend
630 * effort toward recycling unused objects in order to make the memory
631 * they currently occupy available for quick reuse. When control
632 * returns from the method call, the virtual machine has made
633 * its best effort to recycle all discarded objects.
634 * <p>
635 * The name <code>gc</code> stands for "garbage
636 * collector". The virtual machine performs this recycling
637 * process automatically as needed, in a separate thread, even if the
638 * <code>gc</code> method is not invoked explicitly.
639 * <p>
640 * The method {@link System#gc()} is the conventional and convenient
641 * means of invoking this method.
642 */
643 public native void gc();
644
645 /* Wormhole for calling java.lang.ref.Finalizer.runFinalization */
646 private static native void runFinalization0();
647
648 /**
649 * Runs the finalization methods of any objects pending finalization.
650 * Calling this method suggests that the Java virtual machine expend
651 * effort toward running the <code>finalize</code> methods of objects
652 * that have been found to be discarded but whose <code>finalize</code>
653 * methods have not yet been run. When control returns from the
654 * method call, the virtual machine has made a best effort to
655 * complete all outstanding finalizations.
656 * <p>
657 * The virtual machine performs the finalization process
658 * automatically as needed, in a separate thread, if the
659 * <code>runFinalization</code> method is not invoked explicitly.
660 * <p>
661 * The method {@link System#runFinalization()} is the conventional
662 * and convenient means of invoking this method.
663 *
664 * @see java.lang.Object#finalize()
665 */
666 public void runFinalization() {
667 runFinalization0();
668 }
669
670 /**
671 * Enables/Disables tracing of instructions.
672 * If the <code>boolean</code> argument is <code>true</code>, this
673 * method suggests that the Java virtual machine emit debugging
674 * information for each instruction in the virtual machine as it
675 * is executed. The format of this information, and the file or other
676 * output stream to which it is emitted, depends on the host environment.
677 * The virtual machine may ignore this request if it does not support
678 * this feature. The destination of the trace output is system
679 * dependent.
680 * <p>
681 * If the <code>boolean</code> argument is <code>false</code>, this
682 * method causes the virtual machine to stop performing the
683 * detailed instruction trace it is performing.
684 *
685 * @param on <code>true</code> to enable instruction tracing;
686 * <code>false</code> to disable this feature.
687 */
688 public native void traceInstructions(boolean on);
689
690 /**
691 * Enables/Disables tracing of method calls.
692 * If the <code>boolean</code> argument is <code>true</code>, this
693 * method suggests that the Java virtual machine emit debugging
694 * information for each method in the virtual machine as it is
695 * called. The format of this information, and the file or other output
696 * stream to which it is emitted, depends on the host environment. The
697 * virtual machine may ignore this request if it does not support
698 * this feature.
699 * <p>
700 * Calling this method with argument false suggests that the
701 * virtual machine cease emitting per-call debugging information.
702 *
703 * @param on <code>true</code> to enable instruction tracing;
704 * <code>false</code> to disable this feature.
705 */
706 public native void traceMethodCalls(boolean on);
707
708 /**
709 * Loads the native library specified by the filename argument. The filename
710 * argument must be an absolute path name.
711 * (for example
712 * <code>Runtime.getRuntime().load("/home/avh/lib/libX11.so");</code>).
713 *
714 * If the filename argument, when stripped of any platform-specific library
715 * prefix, path, and file extension, indicates a library whose name is,
716 * for example, L, and a native library called L is statically linked
717 * with the VM, then the JNI_OnLoad_L function exported by the library
718 * is invoked rather than attempting to load a dynamic library.
719 * A filename matching the argument does not have to exist in the file
720 * system. See the JNI Specification for more details.
721 *
722 * Otherwise, the filename argument is mapped to a native library image in
723 * an implementation-dependent manner.
724 * <p>
725 * First, if there is a security manager, its <code>checkLink</code>
726 * method is called with the <code>filename</code> as its argument.
727 * This may result in a security exception.
728 * <p>
729 * This is similar to the method {@link #loadLibrary(String)}, but it
730 * accepts a general file name as an argument rather than just a library
731 * name, allowing any file of native code to be loaded.
732 * <p>
733 * The method {@link System#load(String)} is the conventional and
734 * convenient means of invoking this method.
735 *
736 * @param filename the file to load.
737 * @exception SecurityException if a security manager exists and its
738 * <code>checkLink</code> method doesn‘t allow
739 * loading of the specified dynamic library
740 * @exception UnsatisfiedLinkError if either the filename is not an
741 * absolute path name, the native library is not statically
742 * linked with the VM, or the library cannot be mapped to
743 * a native library image by the host system.
744 * @exception NullPointerException if <code>filename</code> is
745 * <code>null</code>
746 * @see java.lang.Runtime#getRuntime()
747 * @see java.lang.SecurityException
748 * @see java.lang.SecurityManager#checkLink(java.lang.String)
749 */
750 @CallerSensitive
751 public void load(String filename) {
752 load0(Reflection.getCallerClass(), filename);
753 }
754
755 synchronized void load0(Class<?> fromClass, String filename) {
756 SecurityManager security = System.getSecurityManager();
757 if (security != null) {
758 security.checkLink(filename);
759 }
760 if (!(new File(filename).isAbsolute())) {
761 throw new UnsatisfiedLinkError(
762 "Expecting an absolute path of the library: " + filename);
763 }
764 ClassLoader.loadLibrary(fromClass, filename, true);
765 }
766
767 /**
768 * Loads the native library specified by the <code>libname</code>
769 * argument. The <code>libname</code> argument must not contain any platform
770 * specific prefix, file extension or path. If a native library
771 * called <code>libname</code> is statically linked with the VM, then the
772 * JNI_OnLoad_<code>libname</code> function exported by the library is invoked.
773 * See the JNI Specification for more details.
774 *
775 * Otherwise, the libname argument is loaded from a system library
776 * location and mapped to a native library image in an implementation-
777 * dependent manner.
778 * <p>
779 * First, if there is a security manager, its <code>checkLink</code>
780 * method is called with the <code>libname</code> as its argument.
781 * This may result in a security exception.
782 * <p>
783 * The method {@link System#loadLibrary(String)} is the conventional
784 * and convenient means of invoking this method. If native
785 * methods are to be used in the implementation of a class, a standard
786 * strategy is to put the native code in a library file (call it
787 * <code>LibFile</code>) and then to put a static initializer:
788 * <blockquote><pre>
789 * static { System.loadLibrary("LibFile"); }
790 * </pre></blockquote>
791 * within the class declaration. When the class is loaded and
792 * initialized, the necessary native code implementation for the native
793 * methods will then be loaded as well.
794 * <p>
795 * If this method is called more than once with the same library
796 * name, the second and subsequent calls are ignored.
797 *
798 * @param libname the name of the library.
799 * @exception SecurityException if a security manager exists and its
800 * <code>checkLink</code> method doesn‘t allow
801 * loading of the specified dynamic library
802 * @exception UnsatisfiedLinkError if either the libname argument
803 * contains a file path, the native library is not statically
804 * linked with the VM, or the library cannot be mapped to a
805 * native library image by the host system.
806 * @exception NullPointerException if <code>libname</code> is
807 * <code>null</code>
808 * @see java.lang.SecurityException
809 * @see java.lang.SecurityManager#checkLink(java.lang.String)
810 */
811 @CallerSensitive
812 public void loadLibrary(String libname) {
813 loadLibrary0(Reflection.getCallerClass(), libname);
814 }
815
816 synchronized void loadLibrary0(Class<?> fromClass, String libname) {
817 SecurityManager security = System.getSecurityManager();
818 if (security != null) {
819 security.checkLink(libname);
820 }
821 if (libname.indexOf((int)File.separatorChar) != -1) {
822 throw new UnsatisfiedLinkError(
823 "Directory separator should not appear in library name: " + libname);
824 }
825 ClassLoader.loadLibrary(fromClass, libname, false);
826 }
827
828 /**
829 * Creates a localized version of an input stream. This method takes
830 * an <code>InputStream</code> and returns an <code>InputStream</code>
831 * equivalent to the argument in all respects except that it is
832 * localized: as characters in the local character set are read from
833 * the stream, they are automatically converted from the local
834 * character set to Unicode.
835 * <p>
836 * If the argument is already a localized stream, it may be returned
837 * as the result.
838 *
839 * @param in InputStream to localize
840 * @return a localized input stream
841 * @see java.io.InputStream
842 * @see java.io.BufferedReader#BufferedReader(java.io.Reader)
843 * @see java.io.InputStreamReader#InputStreamReader(java.io.InputStream)
844 * @deprecated As of JDK 1.1, the preferred way to translate a byte
845 * stream in the local encoding into a character stream in Unicode is via
846 * the <code>InputStreamReader</code> and <code>BufferedReader</code>
847 * classes.
848 */
849 @Deprecated
850 public InputStream getLocalizedInputStream(InputStream in) {
851 return in;
852 }
853
854 /**
855 * Creates a localized version of an output stream. This method
856 * takes an <code>OutputStream</code> and returns an
857 * <code>OutputStream</code> equivalent to the argument in all respects
858 * except that it is localized: as Unicode characters are written to
859 * the stream, they are automatically converted to the local
860 * character set.
861 * <p>
862 * If the argument is already a localized stream, it may be returned
863 * as the result.
864 *
865 * @deprecated As of JDK 1.1, the preferred way to translate a
866 * Unicode character stream into a byte stream in the local encoding is via
867 * the <code>OutputStreamWriter</code>, <code>BufferedWriter</code>, and
868 * <code>PrintWriter</code> classes.
869 *
870 * @param out OutputStream to localize
871 * @return a localized output stream
872 * @see java.io.OutputStream
873 * @see java.io.BufferedWriter#BufferedWriter(java.io.Writer)
874 * @see java.io.OutputStreamWriter#OutputStreamWriter(java.io.OutputStream)
875 * @see java.io.PrintWriter#PrintWriter(java.io.OutputStream)
876 */
877 @Deprecated
878 public OutputStream getLocalizedOutputStream(OutputStream out) {
879 return out;
880 }
881
882 }
类的内部定义
RunTime.exec() 用来执行特定的
/**
* Executes the specified string command in a separate process with the
* specified environment.
*
线程阻塞解决
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时间： 2024-11-07 19:32:57