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28 import java.util.Properties;
29 import java.util.PropertyPermission;
30 import java.util.StringTokenizer;
31 import java.security.AccessController;
32 import java.security.PrivilegedAction;
33 import java.security.AllPermission;
34 import java.nio.channels.Channel;
35 import java.nio.channels.spi.SelectorProvider;
36 import sun.nio.ch.Interruptible;
37 import sun.reflect.Reflection;
38 import sun.security.util.SecurityConstants;
39 import sun.reflect.annotation.AnnotationType;
42 * The <code>System</code> class contains several useful class fields
43 * and methods. It cannot be instantiated.
45 * <p>Among the facilities provided by the <code>System</code> class
46 * are standard input, standard output, and error output streams;
47 * access to externally defined properties and environment
48 * variables; a means of loading files and libraries; and a utility
49 * method for quickly copying a portion of an array.
54 public final class System {
56 /* register the natives via the static initializer.
58 * VM will invoke the initializeSystemClass method to complete
59 * the initialization for this class separated from clinit.
60 * Note that to use properties set by the VM, see the constraints
61 * described in the initializeSystemClass method.
63 private static native void registerNatives();
68 /** Don't let anyone instantiate this class */
73 * The "standard" input stream. This stream is already
74 * open and ready to supply input data. Typically this stream
75 * corresponds to keyboard input or another input source specified by
76 * the host environment or user.
78 public final static InputStream in = null;
81 * The "standard" output stream. This stream is already
82 * open and ready to accept output data. Typically this stream
83 * corresponds to display output or another output destination
84 * specified by the host environment or user.
86 * For simple stand-alone Java applications, a typical way to write
87 * a line of output data is:
89 * System.out.println(data)
92 * See the <code>println</code> methods in class <code>PrintStream</code>.
94 * @see java.io.PrintStream#println()
95 * @see java.io.PrintStream#println(boolean)
96 * @see java.io.PrintStream#println(char)
97 * @see java.io.PrintStream#println(char[])
98 * @see java.io.PrintStream#println(double)
99 * @see java.io.PrintStream#println(float)
100 * @see java.io.PrintStream#println(int)
101 * @see java.io.PrintStream#println(long)
102 * @see java.io.PrintStream#println(java.lang.Object)
103 * @see java.io.PrintStream#println(java.lang.String)
105 public final static PrintStream out = null;
108 * The "standard" error output stream. This stream is already
109 * open and ready to accept output data.
111 * Typically this stream corresponds to display output or another
112 * output destination specified by the host environment or user. By
113 * convention, this output stream is used to display error messages
114 * or other information that should come to the immediate attention
115 * of a user even if the principal output stream, the value of the
116 * variable <code>out</code>, has been redirected to a file or other
117 * destination that is typically not continuously monitored.
119 public final static PrintStream err = null;
121 /* The security manager for the system.
123 private static volatile SecurityManager security = null;
126 * Reassigns the "standard" input stream.
128 * <p>First, if there is a security manager, its <code>checkPermission</code>
129 * method is called with a <code>RuntimePermission("setIO")</code> permission
130 * to see if it's ok to reassign the "standard" input stream.
133 * @param in the new standard input stream.
135 * @throws SecurityException
136 * if a security manager exists and its
137 * <code>checkPermission</code> method doesn't allow
138 * reassigning of the standard input stream.
140 * @see SecurityManager#checkPermission
141 * @see java.lang.RuntimePermission
145 public static void setIn(InputStream in) {
151 * Reassigns the "standard" output stream.
153 * <p>First, if there is a security manager, its <code>checkPermission</code>
154 * method is called with a <code>RuntimePermission("setIO")</code> permission
155 * to see if it's ok to reassign the "standard" output stream.
157 * @param out the new standard output stream
159 * @throws SecurityException
160 * if a security manager exists and its
161 * <code>checkPermission</code> method doesn't allow
162 * reassigning of the standard output stream.
164 * @see SecurityManager#checkPermission
165 * @see java.lang.RuntimePermission
169 public static void setOut(PrintStream out) {
175 * Reassigns the "standard" error output stream.
177 * <p>First, if there is a security manager, its <code>checkPermission</code>
178 * method is called with a <code>RuntimePermission("setIO")</code> permission
179 * to see if it's ok to reassign the "standard" error output stream.
181 * @param err the new standard error output stream.
183 * @throws SecurityException
184 * if a security manager exists and its
185 * <code>checkPermission</code> method doesn't allow
186 * reassigning of the standard error output stream.
188 * @see SecurityManager#checkPermission
189 * @see java.lang.RuntimePermission
193 public static void setErr(PrintStream err) {
198 private static volatile Console cons = null;
200 * Returns the unique {@link java.io.Console Console} object associated
201 * with the current Java virtual machine, if any.
203 * @return The system console, if any, otherwise <tt>null</tt>.
207 public static Console console() {
209 synchronized (System.class) {
210 cons = sun.misc.SharedSecrets.getJavaIOAccess().console();
217 * Returns the channel inherited from the entity that created this
218 * Java virtual machine.
220 * <p> This method returns the channel obtained by invoking the
221 * {@link java.nio.channels.spi.SelectorProvider#inheritedChannel
222 * inheritedChannel} method of the system-wide default
223 * {@link java.nio.channels.spi.SelectorProvider} object. </p>
225 * <p> In addition to the network-oriented channels described in
226 * {@link java.nio.channels.spi.SelectorProvider#inheritedChannel
227 * inheritedChannel}, this method may return other kinds of
228 * channels in the future.
230 * @return The inherited channel, if any, otherwise <tt>null</tt>.
232 * @throws IOException
233 * If an I/O error occurs
235 * @throws SecurityException
236 * If a security manager is present and it does not
237 * permit access to the channel.
241 public static Channel inheritedChannel() throws IOException {
242 return SelectorProvider.provider().inheritedChannel();
245 private static void checkIO() {
246 SecurityManager sm = getSecurityManager();
248 sm.checkPermission(new RuntimePermission("setIO"));
252 private static native void setIn0(InputStream in);
253 private static native void setOut0(PrintStream out);
254 private static native void setErr0(PrintStream err);
257 * Sets the System security.
259 * <p> If there is a security manager already installed, this method first
260 * calls the security manager's <code>checkPermission</code> method
261 * with a <code>RuntimePermission("setSecurityManager")</code>
262 * permission to ensure it's ok to replace the existing
264 * This may result in throwing a <code>SecurityException</code>.
266 * <p> Otherwise, the argument is established as the current
267 * security manager. If the argument is <code>null</code> and no
268 * security manager has been established, then no action is taken and
269 * the method simply returns.
271 * @param s the security manager.
272 * @exception SecurityException if the security manager has already
273 * been set and its <code>checkPermission</code> method
274 * doesn't allow it to be replaced.
275 * @see #getSecurityManager
276 * @see SecurityManager#checkPermission
277 * @see java.lang.RuntimePermission
280 void setSecurityManager(final SecurityManager s) {
282 s.checkPackageAccess("java.lang");
283 } catch (Exception e) {
286 setSecurityManager0(s);
289 private static synchronized
290 void setSecurityManager0(final SecurityManager s) {
291 SecurityManager sm = getSecurityManager();
293 // ask the currently installed security manager if we
295 sm.checkPermission(new RuntimePermission
296 ("setSecurityManager"));
299 if ((s != null) && (s.getClass().getClassLoader() != null)) {
300 // New security manager class is not on bootstrap classpath.
301 // Cause policy to get initialized before we install the new
302 // security manager, in order to prevent infinite loops when
303 // trying to initialize the policy (which usually involves
304 // accessing some security and/or system properties, which in turn
305 // calls the installed security manager's checkPermission method
306 // which will loop infinitely if there is a non-system class
307 // (in this case: the new security manager class) on the stack).
308 AccessController.doPrivileged(new PrivilegedAction<Object>() {
309 public Object run() {
310 s.getClass().getProtectionDomain().implies
311 (SecurityConstants.ALL_PERMISSION);
321 * Gets the system security interface.
323 * @return if a security manager has already been established for the
324 * current application, then that security manager is returned;
325 * otherwise, <code>null</code> is returned.
326 * @see #setSecurityManager
328 public static SecurityManager getSecurityManager() {
333 * Returns the current time in milliseconds. Note that
334 * while the unit of time of the return value is a millisecond,
335 * the granularity of the value depends on the underlying
336 * operating system and may be larger. For example, many
337 * operating systems measure time in units of tens of
340 * <p> See the description of the class <code>Date</code> for
341 * a discussion of slight discrepancies that may arise between
342 * "computer time" and coordinated universal time (UTC).
344 * @return the difference, measured in milliseconds, between
345 * the current time and midnight, January 1, 1970 UTC.
346 * @see java.util.Date
348 public static native long currentTimeMillis();
351 * Returns the current value of the running Java Virtual Machine's
352 * high-resolution time source, in nanoseconds.
354 * <p>This method can only be used to measure elapsed time and is
355 * not related to any other notion of system or wall-clock time.
356 * The value returned represents nanoseconds since some fixed but
357 * arbitrary <i>origin</i> time (perhaps in the future, so values
358 * may be negative). The same origin is used by all invocations of
359 * this method in an instance of a Java virtual machine; other
360 * virtual machine instances are likely to use a different origin.
362 * <p>This method provides nanosecond precision, but not necessarily
363 * nanosecond resolution (that is, how frequently the value changes)
364 * - no guarantees are made except that the resolution is at least as
365 * good as that of {@link #currentTimeMillis()}.
367 * <p>Differences in successive calls that span greater than
368 * approximately 292 years (2<sup>63</sup> nanoseconds) will not
369 * correctly compute elapsed time due to numerical overflow.
371 * <p>The values returned by this method become meaningful only when
372 * the difference between two such values, obtained within the same
373 * instance of a Java virtual machine, is computed.
375 * <p> For example, to measure how long some code takes to execute:
377 * long startTime = System.nanoTime();
378 * // ... the code being measured ...
379 * long estimatedTime = System.nanoTime() - startTime;}</pre>
381 * <p>To compare two nanoTime values
383 * long t0 = System.nanoTime();
385 * long t1 = System.nanoTime();}</pre>
387 * one should use {@code t1 - t0 < 0}, not {@code t1 < t0},
388 * because of the possibility of numerical overflow.
390 * @return the current value of the running Java Virtual Machine's
391 * high-resolution time source, in nanoseconds
394 public static native long nanoTime();
397 * Copies an array from the specified source array, beginning at the
398 * specified position, to the specified position of the destination array.
399 * A subsequence of array components are copied from the source
400 * array referenced by <code>src</code> to the destination array
401 * referenced by <code>dest</code>. The number of components copied is
402 * equal to the <code>length</code> argument. The components at
403 * positions <code>srcPos</code> through
404 * <code>srcPos+length-1</code> in the source array are copied into
405 * positions <code>destPos</code> through
406 * <code>destPos+length-1</code>, respectively, of the destination
409 * If the <code>src</code> and <code>dest</code> arguments refer to the
410 * same array object, then the copying is performed as if the
411 * components at positions <code>srcPos</code> through
412 * <code>srcPos+length-1</code> were first copied to a temporary
413 * array with <code>length</code> components and then the contents of
414 * the temporary array were copied into positions
415 * <code>destPos</code> through <code>destPos+length-1</code> of the
418 * If <code>dest</code> is <code>null</code>, then a
419 * <code>NullPointerException</code> is thrown.
421 * If <code>src</code> is <code>null</code>, then a
422 * <code>NullPointerException</code> is thrown and the destination
423 * array is not modified.
425 * Otherwise, if any of the following is true, an
426 * <code>ArrayStoreException</code> is thrown and the destination is
429 * <li>The <code>src</code> argument refers to an object that is not an
431 * <li>The <code>dest</code> argument refers to an object that is not an
433 * <li>The <code>src</code> argument and <code>dest</code> argument refer
434 * to arrays whose component types are different primitive types.
435 * <li>The <code>src</code> argument refers to an array with a primitive
436 * component type and the <code>dest</code> argument refers to an array
437 * with a reference component type.
438 * <li>The <code>src</code> argument refers to an array with a reference
439 * component type and the <code>dest</code> argument refers to an array
440 * with a primitive component type.
443 * Otherwise, if any of the following is true, an
444 * <code>IndexOutOfBoundsException</code> is
445 * thrown and the destination is not modified:
447 * <li>The <code>srcPos</code> argument is negative.
448 * <li>The <code>destPos</code> argument is negative.
449 * <li>The <code>length</code> argument is negative.
450 * <li><code>srcPos+length</code> is greater than
451 * <code>src.length</code>, the length of the source array.
452 * <li><code>destPos+length</code> is greater than
453 * <code>dest.length</code>, the length of the destination array.
456 * Otherwise, if any actual component of the source array from
457 * position <code>srcPos</code> through
458 * <code>srcPos+length-1</code> cannot be converted to the component
459 * type of the destination array by assignment conversion, an
460 * <code>ArrayStoreException</code> is thrown. In this case, let
461 * <b><i>k</i></b> be the smallest nonnegative integer less than
462 * length such that <code>src[srcPos+</code><i>k</i><code>]</code>
463 * cannot be converted to the component type of the destination
464 * array; when the exception is thrown, source array components from
465 * positions <code>srcPos</code> through
466 * <code>srcPos+</code><i>k</i><code>-1</code>
467 * will already have been copied to destination array positions
468 * <code>destPos</code> through
469 * <code>destPos+</code><i>k</I><code>-1</code> and no other
470 * positions of the destination array will have been modified.
471 * (Because of the restrictions already itemized, this
472 * paragraph effectively applies only to the situation where both
473 * arrays have component types that are reference types.)
475 * @param src the source array.
476 * @param srcPos starting position in the source array.
477 * @param dest the destination array.
478 * @param destPos starting position in the destination data.
479 * @param length the number of array elements to be copied.
480 * @exception IndexOutOfBoundsException if copying would cause
481 * access of data outside array bounds.
482 * @exception ArrayStoreException if an element in the <code>src</code>
483 * array could not be stored into the <code>dest</code> array
484 * because of a type mismatch.
485 * @exception NullPointerException if either <code>src</code> or
486 * <code>dest</code> is <code>null</code>.
488 public static native void arraycopy(Object src, int srcPos,
489 Object dest, int destPos,
493 * Returns the same hash code for the given object as
494 * would be returned by the default method hashCode(),
495 * whether or not the given object's class overrides
497 * The hash code for the null reference is zero.
499 * @param x object for which the hashCode is to be calculated
500 * @return the hashCode
503 public static native int identityHashCode(Object x);
506 * System properties. The following properties are guaranteed to be defined:
508 * <dt>java.version <dd>Java version number
509 * <dt>java.vendor <dd>Java vendor specific string
510 * <dt>java.vendor.url <dd>Java vendor URL
511 * <dt>java.home <dd>Java installation directory
512 * <dt>java.class.version <dd>Java class version number
513 * <dt>java.class.path <dd>Java classpath
514 * <dt>os.name <dd>Operating System Name
515 * <dt>os.arch <dd>Operating System Architecture
516 * <dt>os.version <dd>Operating System Version
517 * <dt>file.separator <dd>File separator ("/" on Unix)
518 * <dt>path.separator <dd>Path separator (":" on Unix)
519 * <dt>line.separator <dd>Line separator ("\n" on Unix)
520 * <dt>user.name <dd>User account name
521 * <dt>user.home <dd>User home directory
522 * <dt>user.dir <dd>User's current working directory
526 private static Properties props;
527 private static native Properties initProperties(Properties props);
530 * Determines the current system properties.
532 * First, if there is a security manager, its
533 * <code>checkPropertiesAccess</code> method is called with no
534 * arguments. This may result in a security exception.
536 * The current set of system properties for use by the
537 * {@link #getProperty(String)} method is returned as a
538 * <code>Properties</code> object. If there is no current set of
539 * system properties, a set of system properties is first created and
540 * initialized. This set of system properties always includes values
541 * for the following keys:
542 * <table summary="Shows property keys and associated values">
544 * <th>Description of Associated Value</th></tr>
545 * <tr><td><code>java.version</code></td>
546 * <td>Java Runtime Environment version</td></tr>
547 * <tr><td><code>java.vendor</code></td>
548 * <td>Java Runtime Environment vendor</td></tr
549 * <tr><td><code>java.vendor.url</code></td>
550 * <td>Java vendor URL</td></tr>
551 * <tr><td><code>java.home</code></td>
552 * <td>Java installation directory</td></tr>
553 * <tr><td><code>java.vm.specification.version</code></td>
554 * <td>Java Virtual Machine specification version</td></tr>
555 * <tr><td><code>java.vm.specification.vendor</code></td>
556 * <td>Java Virtual Machine specification vendor</td></tr>
557 * <tr><td><code>java.vm.specification.name</code></td>
558 * <td>Java Virtual Machine specification name</td></tr>
559 * <tr><td><code>java.vm.version</code></td>
560 * <td>Java Virtual Machine implementation version</td></tr>
561 * <tr><td><code>java.vm.vendor</code></td>
562 * <td>Java Virtual Machine implementation vendor</td></tr>
563 * <tr><td><code>java.vm.name</code></td>
564 * <td>Java Virtual Machine implementation name</td></tr>
565 * <tr><td><code>java.specification.version</code></td>
566 * <td>Java Runtime Environment specification version</td></tr>
567 * <tr><td><code>java.specification.vendor</code></td>
568 * <td>Java Runtime Environment specification vendor</td></tr>
569 * <tr><td><code>java.specification.name</code></td>
570 * <td>Java Runtime Environment specification name</td></tr>
571 * <tr><td><code>java.class.version</code></td>
572 * <td>Java class format version number</td></tr>
573 * <tr><td><code>java.class.path</code></td>
574 * <td>Java class path</td></tr>
575 * <tr><td><code>java.library.path</code></td>
576 * <td>List of paths to search when loading libraries</td></tr>
577 * <tr><td><code>java.io.tmpdir</code></td>
578 * <td>Default temp file path</td></tr>
579 * <tr><td><code>java.compiler</code></td>
580 * <td>Name of JIT compiler to use</td></tr>
581 * <tr><td><code>java.ext.dirs</code></td>
582 * <td>Path of extension directory or directories</td></tr>
583 * <tr><td><code>os.name</code></td>
584 * <td>Operating system name</td></tr>
585 * <tr><td><code>os.arch</code></td>
586 * <td>Operating system architecture</td></tr>
587 * <tr><td><code>os.version</code></td>
588 * <td>Operating system version</td></tr>
589 * <tr><td><code>file.separator</code></td>
590 * <td>File separator ("/" on UNIX)</td></tr>
591 * <tr><td><code>path.separator</code></td>
592 * <td>Path separator (":" on UNIX)</td></tr>
593 * <tr><td><code>line.separator</code></td>
594 * <td>Line separator ("\n" on UNIX)</td></tr>
595 * <tr><td><code>user.name</code></td>
596 * <td>User's account name</td></tr>
597 * <tr><td><code>user.home</code></td>
598 * <td>User's home directory</td></tr>
599 * <tr><td><code>user.dir</code></td>
600 * <td>User's current working directory</td></tr>
603 * Multiple paths in a system property value are separated by the path
604 * separator character of the platform.
606 * Note that even if the security manager does not permit the
607 * <code>getProperties</code> operation, it may choose to permit the
608 * {@link #getProperty(String)} operation.
610 * @return the system properties
611 * @exception SecurityException if a security manager exists and its
612 * <code>checkPropertiesAccess</code> method doesn't allow access
613 * to the system properties.
614 * @see #setProperties
615 * @see java.lang.SecurityException
616 * @see java.lang.SecurityManager#checkPropertiesAccess()
617 * @see java.util.Properties
619 public static Properties getProperties() {
620 SecurityManager sm = getSecurityManager();
622 sm.checkPropertiesAccess();
629 * Returns the system-dependent line separator string. It always
630 * returns the same value - the initial value of the {@linkplain
631 * #getProperty(String) system property} {@code line.separator}.
633 * <p>On UNIX systems, it returns {@code "\n"}; on Microsoft
634 * Windows systems it returns {@code "\r\n"}.
636 public static String lineSeparator() {
637 return lineSeparator;
640 private static String lineSeparator;
643 * Sets the system properties to the <code>Properties</code>
646 * First, if there is a security manager, its
647 * <code>checkPropertiesAccess</code> method is called with no
648 * arguments. This may result in a security exception.
650 * The argument becomes the current set of system properties for use
651 * by the {@link #getProperty(String)} method. If the argument is
652 * <code>null</code>, then the current set of system properties is
655 * @param props the new system properties.
656 * @exception SecurityException if a security manager exists and its
657 * <code>checkPropertiesAccess</code> method doesn't allow access
658 * to the system properties.
659 * @see #getProperties
660 * @see java.util.Properties
661 * @see java.lang.SecurityException
662 * @see java.lang.SecurityManager#checkPropertiesAccess()
664 public static void setProperties(Properties props) {
665 SecurityManager sm = getSecurityManager();
667 sm.checkPropertiesAccess();
670 props = new Properties();
671 initProperties(props);
673 System.props = props;
677 * Gets the system property indicated by the specified key.
679 * First, if there is a security manager, its
680 * <code>checkPropertyAccess</code> method is called with the key as
681 * its argument. This may result in a SecurityException.
683 * If there is no current set of system properties, a set of system
684 * properties is first created and initialized in the same manner as
685 * for the <code>getProperties</code> method.
687 * @param key the name of the system property.
688 * @return the string value of the system property,
689 * or <code>null</code> if there is no property with that key.
691 * @exception SecurityException if a security manager exists and its
692 * <code>checkPropertyAccess</code> method doesn't allow
693 * access to the specified system property.
694 * @exception NullPointerException if <code>key</code> is
696 * @exception IllegalArgumentException if <code>key</code> is empty.
698 * @see java.lang.SecurityException
699 * @see java.lang.SecurityManager#checkPropertyAccess(java.lang.String)
700 * @see java.lang.System#getProperties()
702 public static String getProperty(String key) {
704 SecurityManager sm = getSecurityManager();
706 sm.checkPropertyAccess(key);
709 return props.getProperty(key);
713 * Gets the system property indicated by the specified key.
715 * First, if there is a security manager, its
716 * <code>checkPropertyAccess</code> method is called with the
717 * <code>key</code> as its argument.
719 * If there is no current set of system properties, a set of system
720 * properties is first created and initialized in the same manner as
721 * for the <code>getProperties</code> method.
723 * @param key the name of the system property.
724 * @param def a default value.
725 * @return the string value of the system property,
726 * or the default value if there is no property with that key.
728 * @exception SecurityException if a security manager exists and its
729 * <code>checkPropertyAccess</code> method doesn't allow
730 * access to the specified system property.
731 * @exception NullPointerException if <code>key</code> is
733 * @exception IllegalArgumentException if <code>key</code> is empty.
735 * @see java.lang.SecurityManager#checkPropertyAccess(java.lang.String)
736 * @see java.lang.System#getProperties()
738 public static String getProperty(String key, String def) {
740 SecurityManager sm = getSecurityManager();
742 sm.checkPropertyAccess(key);
745 return props.getProperty(key, def);
749 * Sets the system property indicated by the specified key.
751 * First, if a security manager exists, its
752 * <code>SecurityManager.checkPermission</code> method
753 * is called with a <code>PropertyPermission(key, "write")</code>
754 * permission. This may result in a SecurityException being thrown.
755 * If no exception is thrown, the specified property is set to the given
759 * @param key the name of the system property.
760 * @param value the value of the system property.
761 * @return the previous value of the system property,
762 * or <code>null</code> if it did not have one.
764 * @exception SecurityException if a security manager exists and its
765 * <code>checkPermission</code> method doesn't allow
766 * setting of the specified property.
767 * @exception NullPointerException if <code>key</code> or
768 * <code>value</code> is <code>null</code>.
769 * @exception IllegalArgumentException if <code>key</code> is empty.
771 * @see java.lang.System#getProperty(java.lang.String)
772 * @see java.lang.System#getProperty(java.lang.String, java.lang.String)
773 * @see java.util.PropertyPermission
774 * @see SecurityManager#checkPermission
777 public static String setProperty(String key, String value) {
779 SecurityManager sm = getSecurityManager();
781 sm.checkPermission(new PropertyPermission(key,
782 SecurityConstants.PROPERTY_WRITE_ACTION));
785 return (String) props.setProperty(key, value);
789 * Removes the system property indicated by the specified key.
791 * First, if a security manager exists, its
792 * <code>SecurityManager.checkPermission</code> method
793 * is called with a <code>PropertyPermission(key, "write")</code>
794 * permission. This may result in a SecurityException being thrown.
795 * If no exception is thrown, the specified property is removed.
798 * @param key the name of the system property to be removed.
799 * @return the previous string value of the system property,
800 * or <code>null</code> if there was no property with that key.
802 * @exception SecurityException if a security manager exists and its
803 * <code>checkPropertyAccess</code> method doesn't allow
804 * access to the specified system property.
805 * @exception NullPointerException if <code>key</code> is
807 * @exception IllegalArgumentException if <code>key</code> is empty.
810 * @see java.util.Properties
811 * @see java.lang.SecurityException
812 * @see java.lang.SecurityManager#checkPropertiesAccess()
815 public static String clearProperty(String key) {
817 SecurityManager sm = getSecurityManager();
819 sm.checkPermission(new PropertyPermission(key, "write"));
822 return (String) props.remove(key);
825 private static void checkKey(String key) {
827 throw new NullPointerException("key can't be null");
829 if (key.equals("")) {
830 throw new IllegalArgumentException("key can't be empty");
835 * Gets the value of the specified environment variable. An
836 * environment variable is a system-dependent external named
839 * <p>If a security manager exists, its
840 * {@link SecurityManager#checkPermission checkPermission}
841 * method is called with a
842 * <code>{@link RuntimePermission}("getenv."+name)</code>
843 * permission. This may result in a {@link SecurityException}
844 * being thrown. If no exception is thrown the value of the
845 * variable <code>name</code> is returned.
847 * <p><a name="EnvironmentVSSystemProperties"><i>System
848 * properties</i> and <i>environment variables</i></a> are both
849 * conceptually mappings between names and values. Both
850 * mechanisms can be used to pass user-defined information to a
851 * Java process. Environment variables have a more global effect,
852 * because they are visible to all descendants of the process
853 * which defines them, not just the immediate Java subprocess.
854 * They can have subtly different semantics, such as case
855 * insensitivity, on different operating systems. For these
856 * reasons, environment variables are more likely to have
857 * unintended side effects. It is best to use system properties
858 * where possible. Environment variables should be used when a
859 * global effect is desired, or when an external system interface
860 * requires an environment variable (such as <code>PATH</code>).
862 * <p>On UNIX systems the alphabetic case of <code>name</code> is
863 * typically significant, while on Microsoft Windows systems it is
864 * typically not. For example, the expression
865 * <code>System.getenv("FOO").equals(System.getenv("foo"))</code>
866 * is likely to be true on Microsoft Windows.
868 * @param name the name of the environment variable
869 * @return the string value of the variable, or <code>null</code>
870 * if the variable is not defined in the system environment
871 * @throws NullPointerException if <code>name</code> is <code>null</code>
872 * @throws SecurityException
873 * if a security manager exists and its
874 * {@link SecurityManager#checkPermission checkPermission}
875 * method doesn't allow access to the environment variable
878 * @see ProcessBuilder#environment()
880 public static String getenv(String name) {
881 SecurityManager sm = getSecurityManager();
883 sm.checkPermission(new RuntimePermission("getenv."+name));
886 return ProcessEnvironment.getenv(name);
891 * Returns an unmodifiable string map view of the current system environment.
892 * The environment is a system-dependent mapping from names to
893 * values which is passed from parent to child processes.
895 * <p>If the system does not support environment variables, an
896 * empty map is returned.
898 * <p>The returned map will never contain null keys or values.
899 * Attempting to query the presence of a null key or value will
900 * throw a {@link NullPointerException}. Attempting to query
901 * the presence of a key or value which is not of type
902 * {@link String} will throw a {@link ClassCastException}.
904 * <p>The returned map and its collection views may not obey the
905 * general contract of the {@link Object#equals} and
906 * {@link Object#hashCode} methods.
908 * <p>The returned map is typically case-sensitive on all platforms.
910 * <p>If a security manager exists, its
911 * {@link SecurityManager#checkPermission checkPermission}
912 * method is called with a
913 * <code>{@link RuntimePermission}("getenv.*")</code>
914 * permission. This may result in a {@link SecurityException} being
917 * <p>When passing information to a Java subprocess,
918 * <a href=#EnvironmentVSSystemProperties>system properties</a>
919 * are generally preferred over environment variables.
921 * @return the environment as a map of variable names to values
922 * @throws SecurityException
923 * if a security manager exists and its
924 * {@link SecurityManager#checkPermission checkPermission}
925 * method doesn't allow access to the process environment
926 * @see #getenv(String)
927 * @see ProcessBuilder#environment()
930 public static java.util.Map<String,String> getenv() {
931 SecurityManager sm = getSecurityManager();
933 sm.checkPermission(new RuntimePermission("getenv.*"));
936 return ProcessEnvironment.getenv();
940 * Terminates the currently running Java Virtual Machine. The
941 * argument serves as a status code; by convention, a nonzero status
942 * code indicates abnormal termination.
944 * This method calls the <code>exit</code> method in class
945 * <code>Runtime</code>. This method never returns normally.
947 * The call <code>System.exit(n)</code> is effectively equivalent to
950 * Runtime.getRuntime().exit(n)
951 * </pre></blockquote>
953 * @param status exit status.
954 * @throws SecurityException
955 * if a security manager exists and its <code>checkExit</code>
956 * method doesn't allow exit with the specified status.
957 * @see java.lang.Runtime#exit(int)
959 public static void exit(int status) {
960 Runtime.getRuntime().exit(status);
964 * Runs the garbage collector.
966 * Calling the <code>gc</code> method suggests that the Java Virtual
967 * Machine expend effort toward recycling unused objects in order to
968 * make the memory they currently occupy available for quick reuse.
969 * When control returns from the method call, the Java Virtual
970 * Machine has made a best effort to reclaim space from all discarded
973 * The call <code>System.gc()</code> is effectively equivalent to the
976 * Runtime.getRuntime().gc()
977 * </pre></blockquote>
979 * @see java.lang.Runtime#gc()
981 public static void gc() {
982 Runtime.getRuntime().gc();
986 * Runs the finalization methods of any objects pending finalization.
988 * Calling this method suggests that the Java Virtual Machine expend
989 * effort toward running the <code>finalize</code> methods of objects
990 * that have been found to be discarded but whose <code>finalize</code>
991 * methods have not yet been run. When control returns from the
992 * method call, the Java Virtual Machine has made a best effort to
993 * complete all outstanding finalizations.
995 * The call <code>System.runFinalization()</code> is effectively
996 * equivalent to the call:
998 * Runtime.getRuntime().runFinalization()
999 * </pre></blockquote>
1001 * @see java.lang.Runtime#runFinalization()
1003 public static void runFinalization() {
1004 Runtime.getRuntime().runFinalization();
1008 * Enable or disable finalization on exit; doing so specifies that the
1009 * finalizers of all objects that have finalizers that have not yet been
1010 * automatically invoked are to be run before the Java runtime exits.
1011 * By default, finalization on exit is disabled.
1013 * <p>If there is a security manager,
1014 * its <code>checkExit</code> method is first called
1015 * with 0 as its argument to ensure the exit is allowed.
1016 * This could result in a SecurityException.
1018 * @deprecated This method is inherently unsafe. It may result in
1019 * finalizers being called on live objects while other threads are
1020 * concurrently manipulating those objects, resulting in erratic
1021 * behavior or deadlock.
1022 * @param value indicating enabling or disabling of finalization
1023 * @throws SecurityException
1024 * if a security manager exists and its <code>checkExit</code>
1025 * method doesn't allow the exit.
1027 * @see java.lang.Runtime#exit(int)
1028 * @see java.lang.Runtime#gc()
1029 * @see java.lang.SecurityManager#checkExit(int)
1033 public static void runFinalizersOnExit(boolean value) {
1034 Runtime.getRuntime().runFinalizersOnExit(value);
1038 * Loads a code file with the specified filename from the local file
1039 * system as a dynamic library. The filename
1040 * argument must be a complete path name.
1042 * The call <code>System.load(name)</code> is effectively equivalent
1045 * Runtime.getRuntime().load(name)
1046 * </pre></blockquote>
1048 * @param filename the file to load.
1049 * @exception SecurityException if a security manager exists and its
1050 * <code>checkLink</code> method doesn't allow
1051 * loading of the specified dynamic library
1052 * @exception UnsatisfiedLinkError if the file does not exist.
1053 * @exception NullPointerException if <code>filename</code> is
1055 * @see java.lang.Runtime#load(java.lang.String)
1056 * @see java.lang.SecurityManager#checkLink(java.lang.String)
1058 public static void load(String filename) {
1059 Runtime.getRuntime().load0(getCallerClass(), filename);
1063 * Loads the system library specified by the <code>libname</code>
1064 * argument. The manner in which a library name is mapped to the
1065 * actual system library is system dependent.
1067 * The call <code>System.loadLibrary(name)</code> is effectively
1068 * equivalent to the call
1070 * Runtime.getRuntime().loadLibrary(name)
1071 * </pre></blockquote>
1073 * @param libname the name of the library.
1074 * @exception SecurityException if a security manager exists and its
1075 * <code>checkLink</code> method doesn't allow
1076 * loading of the specified dynamic library
1077 * @exception UnsatisfiedLinkError if the library does not exist.
1078 * @exception NullPointerException if <code>libname</code> is
1080 * @see java.lang.Runtime#loadLibrary(java.lang.String)
1081 * @see java.lang.SecurityManager#checkLink(java.lang.String)
1083 public static void loadLibrary(String libname) {
1084 Runtime.getRuntime().loadLibrary0(getCallerClass(), libname);
1088 * Maps a library name into a platform-specific string representing
1091 * @param libname the name of the library.
1092 * @return a platform-dependent native library name.
1093 * @exception NullPointerException if <code>libname</code> is
1095 * @see java.lang.System#loadLibrary(java.lang.String)
1096 * @see java.lang.ClassLoader#findLibrary(java.lang.String)
1099 public static native String mapLibraryName(String libname);
1102 * Initialize the system class. Called after thread initialization.
1104 private static void initializeSystemClass() {
1106 // VM might invoke JNU_NewStringPlatform() to set those encoding
1107 // sensitive properties (user.home, user.name, boot.class.path, etc.)
1108 // during "props" initialization, in which it may need access, via
1109 // System.getProperty(), to the related system encoding property that
1110 // have been initialized (put into "props") at early stage of the
1111 // initialization. So make sure the "props" is available at the
1112 // very beginning of the initialization and all system properties to
1113 // be put into it directly.
1114 props = new Properties();
1115 initProperties(props); // initialized by the VM
1117 // There are certain system configurations that may be controlled by
1118 // VM options such as the maximum amount of direct memory and
1119 // Integer cache size used to support the object identity semantics
1120 // of autoboxing. Typically, the library will obtain these values
1121 // from the properties set by the VM. If the properties are for
1122 // internal implementation use only, these properties should be
1123 // removed from the system properties.
1125 // See java.lang.Integer.IntegerCache and the
1126 // sun.misc.VM.saveAndRemoveProperties method for example.
1128 // Save a private copy of the system properties object that
1129 // can only be accessed by the internal implementation. Remove
1130 // certain system properties that are not intended for public access.
1131 sun.misc.VM.saveAndRemoveProperties(props);
1134 lineSeparator = props.getProperty("line.separator");
1135 sun.misc.Version.init();
1137 FileInputStream fdIn = new FileInputStream(FileDescriptor.in);
1138 FileOutputStream fdOut = new FileOutputStream(FileDescriptor.out);
1139 FileOutputStream fdErr = new FileOutputStream(FileDescriptor.err);
1140 setIn0(new BufferedInputStream(fdIn));
1141 setOut0(new PrintStream(new BufferedOutputStream(fdOut, 128), true));
1142 setErr0(new PrintStream(new BufferedOutputStream(fdErr, 128), true));
1143 // Load the zip library now in order to keep java.util.zip.ZipFile
1144 // from trying to use itself to load this library later.
1147 // Setup Java signal handlers for HUP, TERM, and INT (where available).
1150 // Initialize any miscellenous operating system settings that need to be
1151 // set for the class libraries. Currently this is no-op everywhere except
1152 // for Windows where the process-wide error mode is set before the java.io
1153 // classes are used.
1154 sun.misc.VM.initializeOSEnvironment();
1156 // Subsystems that are invoked during initialization can invoke
1157 // sun.misc.VM.isBooted() in order to avoid doing things that should
1158 // wait until the application class loader has been set up.
1159 sun.misc.VM.booted();
1161 // The main thread is not added to its thread group in the same
1162 // way as other threads; we must do it ourselves here.
1163 Thread current = Thread.currentThread();
1164 current.getThreadGroup().add(current);
1166 // register shared secrets
1167 setJavaLangAccess();
1170 private static void setJavaLangAccess() {
1171 // Allow privileged classes outside of java.lang
1172 sun.misc.SharedSecrets.setJavaLangAccess(new sun.misc.JavaLangAccess(){
1173 public sun.reflect.ConstantPool getConstantPool(Class klass) {
1174 return klass.getConstantPool();
1176 public void setAnnotationType(Class klass, AnnotationType type) {
1177 klass.setAnnotationType(type);
1179 public AnnotationType getAnnotationType(Class klass) {
1180 return klass.getAnnotationType();
1182 public <E extends Enum<E>>
1183 E[] getEnumConstantsShared(Class<E> klass) {
1184 return klass.getEnumConstantsShared();
1186 public void blockedOn(Thread t, Interruptible b) {
1189 public void registerShutdownHook(int slot, boolean registerShutdownInProgress, Runnable hook) {
1190 Shutdown.add(slot, registerShutdownInProgress, hook);
1192 public int getStackTraceDepth(Throwable t) {
1193 return t.getStackTraceDepth();
1195 public StackTraceElement getStackTraceElement(Throwable t, int i) {
1196 return t.getStackTraceElement(i);
1201 /* returns the class of the caller. */
1202 static Class<?> getCallerClass() {
1203 // NOTE use of more generic Reflection.getCallerClass()
1204 return Reflection.getCallerClass(3);