001    /* System.java -- useful methods to interface with the system
002       Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007
003       Free Software Foundation, Inc.
004    
005    This file is part of GNU Classpath.
006    
007    GNU Classpath is free software; you can redistribute it and/or modify
008    it under the terms of the GNU General Public License as published by
009    the Free Software Foundation; either version 2, or (at your option)
010    any later version.
011    
012    GNU Classpath is distributed in the hope that it will be useful, but
013    WITHOUT ANY WARRANTY; without even the implied warranty of
014    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
015    General Public License for more details.
016    
017    You should have received a copy of the GNU General Public License
018    along with GNU Classpath; see the file COPYING.  If not, write to the
019    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
020    02110-1301 USA.
021    
022    Linking this library statically or dynamically with other modules is
023    making a combined work based on this library.  Thus, the terms and
024    conditions of the GNU General Public License cover the whole
025    combination.
026    
027    As a special exception, the copyright holders of this library give you
028    permission to link this library with independent modules to produce an
029    executable, regardless of the license terms of these independent
030    modules, and to copy and distribute the resulting executable under
031    terms of your choice, provided that you also meet, for each linked
032    independent module, the terms and conditions of the license of that
033    module.  An independent module is a module which is not derived from
034    or based on this library.  If you modify this library, you may extend
035    this exception to your version of the library, but you are not
036    obligated to do so.  If you do not wish to do so, delete this
037    exception statement from your version. */
038    
039    
040    package java.lang;
041    
042    import gnu.classpath.SystemProperties;
043    
044    import java.io.BufferedInputStream;
045    import java.io.BufferedOutputStream;
046    import java.io.FileDescriptor;
047    import java.io.FileInputStream;
048    import java.io.FileOutputStream;
049    import java.io.IOException;
050    import java.io.InputStream;
051    import java.io.PrintStream;
052    import java.nio.channels.Channel;
053    import java.nio.channels.spi.SelectorProvider;
054    import java.util.AbstractCollection;
055    import java.util.ArrayList;
056    import java.util.Collection;
057    import java.util.Collections;
058    import java.util.HashMap;
059    import java.util.Iterator;
060    import java.util.List;
061    import java.util.Map;
062    import java.util.Set;
063    import java.util.Properties;
064    import java.util.PropertyPermission;
065    
066    /**
067     * System represents system-wide resources; things that represent the
068     * general environment.  As such, all methods are static.
069     *
070     * @author John Keiser
071     * @author Eric Blake (ebb9@email.byu.edu)
072     * @since 1.0
073     * @status still missing 1.4 functionality
074     */
075    public final class System
076    {
077      // WARNING: System is a CORE class in the bootstrap cycle. See the comments
078      // in vm/reference/java/lang/Runtime for implications of this fact.
079    
080      /**
081       * The standard InputStream. This is assigned at startup and starts its
082       * life perfectly valid. Although it is marked final, you can change it
083       * using {@link #setIn(InputStream)} through some hefty VM magic.
084       *
085       * <p>This corresponds to the C stdin and C++ cin variables, which
086       * typically input from the keyboard, but may be used to pipe input from
087       * other processes or files.  That should all be transparent to you,
088       * however.
089       */
090      public static final InputStream in
091        = new BufferedInputStream(new FileInputStream(FileDescriptor.in));
092      /**
093       * The standard output PrintStream.  This is assigned at startup and
094       * starts its life perfectly valid. Although it is marked final, you can
095       * change it using {@link #setOut(PrintStream)} through some hefty VM magic.
096       *
097       * <p>This corresponds to the C stdout and C++ cout variables, which
098       * typically output normal messages to the screen, but may be used to pipe
099       * output to other processes or files.  That should all be transparent to
100       * you, however.
101       */
102      public static final PrintStream out
103        = new PrintStream(new BufferedOutputStream(new FileOutputStream(FileDescriptor.out)), true);
104      /**
105       * The standard output PrintStream.  This is assigned at startup and
106       * starts its life perfectly valid. Although it is marked final, you can
107       * change it using {@link #setErr(PrintStream)} through some hefty VM magic.
108       *
109       * <p>This corresponds to the C stderr and C++ cerr variables, which
110       * typically output error messages to the screen, but may be used to pipe
111       * output to other processes or files.  That should all be transparent to
112       * you, however.
113       */
114      public static final PrintStream err
115        = new PrintStream(new BufferedOutputStream(new FileOutputStream(FileDescriptor.err)), true);
116    
117      /**
118       * A cached copy of the environment variable map.
119       */
120      private static Map<String,String> environmentMap;
121    
122      /**
123       * This class is uninstantiable.
124       */
125      private System()
126      {
127      }
128    
129      /**
130       * Set {@link #in} to a new InputStream. This uses some VM magic to change
131       * a "final" variable, so naturally there is a security check,
132       * <code>RuntimePermission("setIO")</code>.
133       *
134       * @param in the new InputStream
135       * @throws SecurityException if permission is denied
136       * @since 1.1
137       */
138      public static void setIn(InputStream in)
139      {
140        SecurityManager sm = SecurityManager.current; // Be thread-safe.
141        if (sm != null)
142          sm.checkPermission(new RuntimePermission("setIO"));
143        setIn0(in);
144      }
145    
146      /**
147       * Set {@link #out} to a new PrintStream. This uses some VM magic to change
148       * a "final" variable, so naturally there is a security check,
149       * <code>RuntimePermission("setIO")</code>.
150       *
151       * @param out the new PrintStream
152       * @throws SecurityException if permission is denied
153       * @since 1.1
154       */
155      public static void setOut(PrintStream out)
156      {
157        SecurityManager sm = SecurityManager.current; // Be thread-safe.
158        if (sm != null)
159          sm.checkPermission(new RuntimePermission("setIO"));
160        
161        setOut0(out);
162      }
163    
164      /**
165       * Set {@link #err} to a new PrintStream. This uses some VM magic to change
166       * a "final" variable, so naturally there is a security check,
167       * <code>RuntimePermission("setIO")</code>.
168       *
169       * @param err the new PrintStream
170       * @throws SecurityException if permission is denied
171       * @since 1.1
172       */
173      public static void setErr(PrintStream err)
174      {
175        SecurityManager sm = SecurityManager.current; // Be thread-safe.
176        if (sm != null)
177          sm.checkPermission(new RuntimePermission("setIO"));
178        setErr0(err);
179      }
180    
181      /**
182       * Set the current SecurityManager. If a security manager already exists,
183       * then <code>RuntimePermission("setSecurityManager")</code> is checked
184       * first. Since this permission is denied by the default security manager,
185       * setting the security manager is often an irreversible action.
186       *
187       * @param sm the new SecurityManager
188       * @throws SecurityException if permission is denied
189       */
190      public static synchronized void setSecurityManager(SecurityManager sm)
191      {
192        // Implementation note: the field lives in SecurityManager because of
193        // bootstrap initialization issues. This method is synchronized so that
194        // no other thread changes it to null before this thread makes the change.
195        if (SecurityManager.current != null)
196          SecurityManager.current.checkPermission
197            (new RuntimePermission("setSecurityManager"));
198        SecurityManager.current = sm;
199      }
200    
201      /**
202       * Get the current SecurityManager. If the SecurityManager has not been
203       * set yet, then this method returns null.
204       *
205       * @return the current SecurityManager, or null
206       */
207      public static SecurityManager getSecurityManager()
208      {
209        return SecurityManager.current;
210      }
211    
212      /**
213       * Get the current time, measured in the number of milliseconds from the
214       * beginning of Jan. 1, 1970. This is gathered from the system clock, with
215       * any attendant incorrectness (it may be timezone dependent).
216       *
217       * @return the current time
218       * @see java.util.Date
219       */
220      public static native long currentTimeMillis();
221    
222      /**
223       * Get the current time, measured in nanoseconds.  The result is as
224       * precise as possible, and is measured against a fixed epoch.
225       * However, unlike currentTimeMillis(), the epoch chosen is
226       * arbitrary and may vary by platform, etc.
227       * @since 1.5
228       */
229      public static native long nanoTime();
230    
231      /**
232       * Copy one array onto another from <code>src[srcStart]</code> ...
233       * <code>src[srcStart+len-1]</code> to <code>dest[destStart]</code> ...
234       * <code>dest[destStart+len-1]</code>. First, the arguments are validated:
235       * neither array may be null, they must be of compatible types, and the
236       * start and length must fit within both arrays. Then the copying starts,
237       * and proceeds through increasing slots.  If src and dest are the same
238       * array, this will appear to copy the data to a temporary location first.
239       * An ArrayStoreException in the middle of copying will leave earlier
240       * elements copied, but later elements unchanged.
241       *
242       * @param src the array to copy elements from
243       * @param srcStart the starting position in src
244       * @param dest the array to copy elements to
245       * @param destStart the starting position in dest
246       * @param len the number of elements to copy
247       * @throws NullPointerException if src or dest is null
248       * @throws ArrayStoreException if src or dest is not an array, if they are
249       *         not compatible array types, or if an incompatible runtime type
250       *         is stored in dest
251       * @throws IndexOutOfBoundsException if len is negative, or if the start or
252       *         end copy position in either array is out of bounds
253       */
254      public static native void arraycopy(Object src, int srcStart,
255                                          Object dest, int destStart, int len);
256    
257      /**
258       * Get a hash code computed by the VM for the Object. This hash code will
259       * be the same as Object's hashCode() method.  It is usually some
260       * convolution of the pointer to the Object internal to the VM.  It
261       * follows standard hash code rules, in that it will remain the same for a
262       * given Object for the lifetime of that Object.
263       *
264       * @param o the Object to get the hash code for
265       * @return the VM-dependent hash code for this Object
266       * @since 1.1
267       */
268      public static native int identityHashCode(Object o);
269    
270      /**
271       * Get all the system properties at once. A security check may be performed,
272       * <code>checkPropertiesAccess</code>. Note that a security manager may
273       * allow getting a single property, but not the entire group.
274       *
275       * <p>The required properties include:
276       * <dl>
277       * <dt>java.version</dt>         <dd>Java version number</dd>
278       * <dt>java.vendor</dt>          <dd>Java vendor specific string</dd>
279       * <dt>java.vendor.url</dt>      <dd>Java vendor URL</dd>
280       * <dt>java.home</dt>            <dd>Java installation directory</dd>
281       * <dt>java.vm.specification.version</dt> <dd>VM Spec version</dd>
282       * <dt>java.vm.specification.vendor</dt>  <dd>VM Spec vendor</dd>
283       * <dt>java.vm.specification.name</dt>    <dd>VM Spec name</dd>
284       * <dt>java.vm.version</dt>      <dd>VM implementation version</dd>
285       * <dt>java.vm.vendor</dt>       <dd>VM implementation vendor</dd>
286       * <dt>java.vm.name</dt>         <dd>VM implementation name</dd>
287       * <dt>java.specification.version</dt>    <dd>Java Runtime Environment version</dd>
288       * <dt>java.specification.vendor</dt>     <dd>Java Runtime Environment vendor</dd>
289       * <dt>java.specification.name</dt>       <dd>Java Runtime Environment name</dd>
290       * <dt>java.class.version</dt>   <dd>Java class version number</dd>
291       * <dt>java.class.path</dt>      <dd>Java classpath</dd>
292       * <dt>java.library.path</dt>    <dd>Path for finding Java libraries</dd>
293       * <dt>java.io.tmpdir</dt>       <dd>Default temp file path</dd>
294       * <dt>java.compiler</dt>        <dd>Name of JIT to use</dd>
295       * <dt>java.ext.dirs</dt>        <dd>Java extension path</dd>
296       * <dt>os.name</dt>              <dd>Operating System Name</dd>
297       * <dt>os.arch</dt>              <dd>Operating System Architecture</dd>
298       * <dt>os.version</dt>           <dd>Operating System Version</dd>
299       * <dt>file.separator</dt>       <dd>File separator ("/" on Unix)</dd>
300       * <dt>path.separator</dt>       <dd>Path separator (":" on Unix)</dd>
301       * <dt>line.separator</dt>       <dd>Line separator ("\n" on Unix)</dd>
302       * <dt>user.name</dt>            <dd>User account name</dd>
303       * <dt>user.home</dt>            <dd>User home directory</dd>
304       * <dt>user.dir</dt>             <dd>User's current working directory</dd>
305       * </dl>
306       *
307       * In addition, gnu defines several other properties, where ? stands for
308       * each character in '0' through '9':
309       * <dl>
310       * <dt>gnu.classpath.home</dt>         <dd>Path to the classpath libraries.</dd>
311       * <dt>gnu.classpath.version</dt>      <dd>Version of the classpath libraries.</dd>
312       * <dt>gnu.classpath.vm.shortname</dt> <dd>Succinct version of the VM name;
313       *     used for finding property files in file system</dd>
314       * <dt>gnu.classpath.home.url</dt>     <dd> Base URL; used for finding
315       *     property files in file system</dd>
316       * <dt>gnu.cpu.endian</dt>             <dd>big or little</dd>
317       * <dt>gnu.java.io.encoding_scheme_alias.ISO-8859-?</dt>   <dd>8859_?</dd>
318       * <dt>gnu.java.io.encoding_scheme_alias.iso-8859-?</dt>   <dd>8859_?</dd>
319       * <dt>gnu.java.io.encoding_scheme_alias.iso8859_?</dt>    <dd>8859_?</dd>
320       * <dt>gnu.java.io.encoding_scheme_alias.iso-latin-_?</dt> <dd>8859_?</dd>
321       * <dt>gnu.java.io.encoding_scheme_alias.latin?</dt>       <dd>8859_?</dd>
322       * <dt>gnu.java.io.encoding_scheme_alias.UTF-8</dt>        <dd>UTF8</dd>
323       * <dt>gnu.java.io.encoding_scheme_alias.utf-8</dt>        <dd>UTF8</dd>
324       * <dt>gnu.java.util.zoneinfo.dir</dt>    <dd>Root of zoneinfo tree</dd>
325       * </dl>
326       *
327       * @return the system properties, will never be null
328       * @throws SecurityException if permission is denied
329       */
330      public static Properties getProperties()
331      {
332        SecurityManager sm = SecurityManager.current; // Be thread-safe.
333        if (sm != null)
334          sm.checkPropertiesAccess();
335        return SystemProperties.getProperties();
336      }
337    
338      /**
339       * Set all the system properties at once. A security check may be performed,
340       * <code>checkPropertiesAccess</code>. Note that a security manager may
341       * allow setting a single property, but not the entire group. An argument
342       * of null resets the properties to the startup default.
343       *
344       * @param properties the new set of system properties
345       * @throws SecurityException if permission is denied
346       */
347      public static void setProperties(Properties properties)
348      {
349        SecurityManager sm = SecurityManager.current; // Be thread-safe.
350        if (sm != null)
351          sm.checkPropertiesAccess();
352        SystemProperties.setProperties(properties);
353      }
354    
355      /**
356       * Get a single system property by name. A security check may be performed,
357       * <code>checkPropertyAccess(key)</code>.
358       *
359       * @param key the name of the system property to get
360       * @return the property, or null if not found
361       * @throws SecurityException if permission is denied
362       * @throws NullPointerException if key is null
363       * @throws IllegalArgumentException if key is ""
364       */
365      public static String getProperty(String key)
366      {
367        SecurityManager sm = SecurityManager.current; // Be thread-safe.
368        if (sm != null)
369          sm.checkPropertyAccess(key);
370        else if (key.length() == 0)
371          throw new IllegalArgumentException("key can't be empty");
372        return SystemProperties.getProperty(key);
373      }
374    
375      /**
376       * Get a single system property by name. A security check may be performed,
377       * <code>checkPropertyAccess(key)</code>.
378       *
379       * @param key the name of the system property to get
380       * @param def the default
381       * @return the property, or def if not found
382       * @throws SecurityException if permission is denied
383       * @throws NullPointerException if key is null
384       * @throws IllegalArgumentException if key is ""
385       */
386      public static String getProperty(String key, String def)
387      {
388        SecurityManager sm = SecurityManager.current; // Be thread-safe.
389        if (sm != null)
390          sm.checkPropertyAccess(key);
391        return SystemProperties.getProperty(key, def);
392      }
393    
394      /**
395       * Set a single system property by name. A security check may be performed,
396       * <code>checkPropertyAccess(key, "write")</code>.
397       *
398       * @param key the name of the system property to set
399       * @param value the new value
400       * @return the previous value, or null
401       * @throws SecurityException if permission is denied
402       * @throws NullPointerException if key is null
403       * @throws IllegalArgumentException if key is ""
404       * @since 1.2
405       */
406      public static String setProperty(String key, String value)
407      {
408        SecurityManager sm = SecurityManager.current; // Be thread-safe.
409        if (sm != null)
410          sm.checkPermission(new PropertyPermission(key, "write"));
411        return SystemProperties.setProperty(key, value);
412      }
413    
414      /**
415       * Remove a single system property by name. A security check may be
416       * performed, <code>checkPropertyAccess(key, "write")</code>.
417       *
418       * @param key the name of the system property to remove
419       * @return the previous value, or null
420       * @throws SecurityException if permission is denied
421       * @throws NullPointerException if key is null
422       * @throws IllegalArgumentException if key is ""
423       * @since 1.5
424       */
425      public static String clearProperty(String key)
426      {
427        SecurityManager sm = SecurityManager.current; // Be thread-safe.
428        if (sm != null)
429          sm.checkPermission(new PropertyPermission(key, "write"));
430        // This handles both the null pointer exception and the illegal
431        // argument exception.
432        if (key.length() == 0)
433          throw new IllegalArgumentException("key can't be empty");
434        return SystemProperties.remove(key);
435      }
436    
437      /**
438       * Gets the value of an environment variable.
439       *
440       * @param name the name of the environment variable
441       * @return the string value of the variable or null when the
442       *         environment variable is not defined.
443       * @throws NullPointerException
444       * @throws SecurityException if permission is denied
445       * @since 1.5
446       * @specnote This method was deprecated in some JDK releases, but
447       *           was restored in 1.5.
448       */
449      public static String getenv(String name)
450      {
451        if (name == null)
452          throw new NullPointerException();
453        SecurityManager sm = SecurityManager.current; // Be thread-safe.
454        if (sm != null)
455          sm.checkPermission(new RuntimePermission("getenv." + name));
456        return getenv0(name);
457      }
458    
459      /**
460       * <p>
461       * Returns an unmodifiable view of the system environment variables.
462       * If the underlying system does not support environment variables,
463       * an empty map is returned.
464       * </p>
465       * <p>
466       * The returned map is read-only and does not accept queries using
467       * null keys or values, or those of a type other than <code>String</code>.
468       * Attempts to modify the map will throw an
469       * <code>UnsupportedOperationException</code>, while attempts
470       * to pass in a null value will throw a
471       * <code>NullPointerException</code>.  Types other than <code>String</code>
472       * throw a <code>ClassCastException</code>.
473       * </p>
474       * <p>
475       * As the returned map is generated using data from the underlying
476       * platform, it may not comply with the <code>equals()</code>
477       * and <code>hashCode()</code> contracts.  It is also likely that
478       * the keys of this map will be case-sensitive.
479       * </p>
480       * <p>
481       * Use of this method may require a security check for the
482       * RuntimePermission "getenv.*".
483       * </p>
484       *
485       * @return a map of the system environment variables.
486       * @throws SecurityException if the checkPermission method of
487       *         an installed security manager prevents access to
488       *         the system environment variables.
489       * @since 1.5
490       */
491      public static Map<String, String> getenv()
492      {
493        SecurityManager sm = SecurityManager.current; // Be thread-safe.
494        if (sm != null)
495          sm.checkPermission(new RuntimePermission("getenv.*"));
496        if (environmentMap == null)
497          {
498            // List<String> environ = (List<String>)VMSystem.environ();
499            // FIXME
500            List<String> environ = new ArrayList<String>();
501            Map<String,String> variables = new EnvironmentMap();
502            for (String pair : environ)
503              {
504                String[] parts = pair.split("=");
505                variables.put(parts[0], parts[1]);
506              }
507            environmentMap = Collections.unmodifiableMap(variables);
508          }
509        return environmentMap;
510      }
511    
512      /**
513       * Terminate the Virtual Machine. This just calls
514       * <code>Runtime.getRuntime().exit(status)</code>, and never returns.
515       * Obviously, a security check is in order, <code>checkExit</code>.
516       *
517       * @param status the exit status; by convention non-zero is abnormal
518       * @throws SecurityException if permission is denied
519       * @see Runtime#exit(int)
520       */
521      public static void exit(int status)
522      {
523        Runtime.getRuntime().exit(status);
524      }
525    
526      /**
527       * Calls the garbage collector. This is only a hint, and it is up to the
528       * implementation what this hint suggests, but it usually causes a
529       * best-effort attempt to reclaim unused memory from discarded objects.
530       * This calls <code>Runtime.getRuntime().gc()</code>.
531       *
532       * @see Runtime#gc()
533       */
534      public static void gc()
535      {
536        Runtime.getRuntime().gc();
537      }
538    
539      /**
540       * Runs object finalization on pending objects. This is only a hint, and
541       * it is up to the implementation what this hint suggests, but it usually
542       * causes a best-effort attempt to run finalizers on all objects ready
543       * to be reclaimed. This calls
544       * <code>Runtime.getRuntime().runFinalization()</code>.
545       *
546       * @see Runtime#runFinalization()
547       */
548      public static void runFinalization()
549      {
550        Runtime.getRuntime().runFinalization();
551      }
552    
553      /**
554       * Tell the Runtime whether to run finalization before exiting the
555       * JVM.  This is inherently unsafe in multi-threaded applications,
556       * since it can force initialization on objects which are still in use
557       * by live threads, leading to deadlock; therefore this is disabled by
558       * default. There may be a security check, <code>checkExit(0)</code>. This
559       * calls <code>Runtime.getRuntime().runFinalizersOnExit()</code>.
560       *
561       * @param finalizeOnExit whether to run finalizers on exit
562       * @throws SecurityException if permission is denied
563       * @see Runtime#runFinalizersOnExit()
564       * @since 1.1
565       * @deprecated never rely on finalizers to do a clean, thread-safe,
566       *             mop-up from your code
567       */
568      public static void runFinalizersOnExit(boolean finalizeOnExit)
569      {
570        Runtime.getRuntime().runFinalizersOnExit(finalizeOnExit);
571      }
572    
573      /**
574       * Load a code file using its explicit system-dependent filename. A security
575       * check may be performed, <code>checkLink</code>. This just calls
576       * <code>Runtime.getRuntime().load(filename)</code>.
577       *
578       * <p>
579       * The library is loaded using the class loader associated with the
580       * class associated with the invoking method.
581       *
582       * @param filename the code file to load
583       * @throws SecurityException if permission is denied
584       * @throws UnsatisfiedLinkError if the file cannot be loaded
585       * @see Runtime#load(String)
586       */
587      public static void load(String filename)
588      {
589        Runtime.getRuntime().load(filename);
590      }
591    
592      /**
593       * Load a library using its explicit system-dependent filename. A security
594       * check may be performed, <code>checkLink</code>. This just calls
595       * <code>Runtime.getRuntime().load(filename)</code>.
596       *
597       * <p>
598       * The library is loaded using the class loader associated with the
599       * class associated with the invoking method.
600       *
601       * @param libname the library file to load
602       * @throws SecurityException if permission is denied
603       * @throws UnsatisfiedLinkError if the file cannot be loaded
604       * @see Runtime#load(String)
605       */
606      public static void loadLibrary(String libname)
607      {
608        Runtime.getRuntime().loadLibrary(libname);
609      }
610    
611      /**
612       * Convert a library name to its platform-specific variant.
613       *
614       * @param libname the library name, as used in <code>loadLibrary</code>
615       * @return the platform-specific mangling of the name
616       * @since 1.2
617       */
618      public static String mapLibraryName(String libname)
619      {
620        // XXX Fix this!!!!
621        return Runtime.nativeGetLibname("", libname);
622      }
623    
624      /**
625       * Set {@link #in} to a new InputStream.
626       *
627       * @param in the new InputStream
628       * @see #setIn(InputStream)
629       */
630      private static native void setIn0(InputStream in);
631    
632      /**
633       * Set {@link #out} to a new PrintStream.
634       *
635       * @param out the new PrintStream
636       * @see #setOut(PrintStream)
637       */
638      private static native void setOut0(PrintStream out);
639    
640      /**
641       * Set {@link #err} to a new PrintStream.
642       *
643       * @param err the new PrintStream
644       * @see #setErr(PrintStream)
645       */
646      private static native void setErr0(PrintStream err);
647    
648      /**
649       * Gets the value of an environment variable.
650       *
651       * @see #getenv(String)
652       */
653      static native String getenv0(String name);
654    
655      /**
656       * Returns the inherited channel of the VM.
657       *
658       * This wraps the inheritedChannel() call of the system's default
659       * {@link SelectorProvider}.
660       *
661       * @return the inherited channel of the VM
662       *
663       * @throws IOException If an I/O error occurs
664       * @throws SecurityException If an installed security manager denies access
665       *         to RuntimePermission("inheritedChannel")
666       *
667       * @since 1.5
668       */
669      public static Channel inheritedChannel()
670        throws IOException
671      {
672        return SelectorProvider.provider().inheritedChannel();
673      }
674    
675      /**
676       * This is a specialised <code>Collection</code>, providing
677       * the necessary provisions for the collections used by the
678       * environment variable map.  Namely, it prevents
679       * querying anything but <code>String</code>s.
680       *
681       * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
682       */
683      private static class EnvironmentCollection
684        extends AbstractCollection<String>
685      {
686    
687        /**
688         * The wrapped collection.
689         */
690        protected Collection<String> c;
691    
692        /**
693         * Constructs a new environment collection, which
694         * wraps the elements of the supplied collection.
695         *
696         * @param coll the collection to use as a base for
697         *             this collection.
698         */
699        public EnvironmentCollection(Collection<String> coll)
700        {
701          c = coll;
702        }
703            
704        /**
705         * Blocks queries containing a null object or an object which
706         * isn't of type <code>String</code>.  All other queries
707         * are forwarded to the underlying collection.
708         *
709         * @param obj the object to look for.
710         * @return true if the object exists in the collection.
711         * @throws NullPointerException if the specified object is null.
712         * @throws ClassCastException if the specified object is not a String.
713         */
714        public boolean contains(Object obj)
715        {
716          if (obj == null)
717              throw new
718                NullPointerException("This collection does not support " +
719                                     "null values.");
720          if (!(obj instanceof String))
721              throw new
722                ClassCastException("This collection only supports Strings.");
723          return c.contains(obj);
724        }
725        
726        /**
727         * Blocks queries where the collection contains a null object or
728         * an object which isn't of type <code>String</code>.  All other
729         * queries are forwarded to the underlying collection.
730         *
731         * @param coll the collection of objects to look for.
732         * @return true if the collection contains all elements in the collection.
733         * @throws NullPointerException if the collection is null.
734         * @throws NullPointerException if any collection entry is null.
735         * @throws ClassCastException if any collection entry is not a String.
736         */
737        public boolean containsAll(Collection<?> coll)
738        {
739          for (Object o: coll)
740            {
741              if (o == null)
742                  throw new
743                    NullPointerException("This collection does not support " +
744                                         "null values.");
745              if (!(o instanceof String))
746                  throw new
747                    ClassCastException("This collection only supports Strings.");
748            }
749          return c.containsAll(coll);
750        }
751    
752        /**
753         * This returns an iterator over the map elements, with the
754         * same provisions as for the collection and underlying map.
755         *
756         * @return an iterator over the map elements.
757         */
758        public Iterator<String> iterator()
759        {
760          return c.iterator();
761        }
762        
763        /**
764         * Blocks the removal of elements from the collection.
765         *
766         * @return true if the removal was sucessful.
767         * @throws NullPointerException if the collection is null.
768         * @throws NullPointerException if any collection entry is null.
769         * @throws ClassCastException if any collection entry is not a String.
770         */
771        public boolean remove(Object key)
772        {
773          if (key == null)
774              throw new
775                NullPointerException("This collection does not support " +
776                                     "null values.");
777          if (!(key instanceof String))
778              throw new
779                ClassCastException("This collection only supports Strings.");
780          return c.contains(key);
781        }   
782            
783        /**
784         * Blocks the removal of all elements in the specified
785         * collection from the collection.
786         *
787         * @param coll the collection of elements to remove.
788         * @return true if the elements were removed.
789         * @throws NullPointerException if the collection is null.
790         * @throws NullPointerException if any collection entry is null.
791         * @throws ClassCastException if any collection entry is not a String.
792         */
793        public boolean removeAll(Collection<?> coll)
794        {
795          for (Object o: coll)
796            {
797              if (o == null)
798                  throw new
799                    NullPointerException("This collection does not support " +
800                                         "null values.");
801              if (!(o instanceof String))
802                throw new
803                  ClassCastException("This collection only supports Strings.");
804            }
805          return c.removeAll(coll);
806        }
807        
808        /**
809         * Blocks the retention of all elements in the specified
810         * collection from the collection.
811         *
812         * @param c the collection of elements to retain.
813         * @return true if the other elements were removed.
814         * @throws NullPointerException if the collection is null.
815         * @throws NullPointerException if any collection entry is null.
816         * @throws ClassCastException if any collection entry is not a String.
817         */
818        public boolean retainAll(Collection<?> coll)
819        {
820          for (Object o: coll)
821            {
822              if (o == null)
823                  throw new
824                    NullPointerException("This collection does not support " +
825                                         "null values.");
826              if (!(o instanceof String))
827                throw new
828                  ClassCastException("This collection only supports Strings.");
829            }
830          return c.containsAll(coll);
831        }
832    
833        /**
834         * This simply calls the same method on the wrapped
835         * collection.
836         *
837         * @return the size of the underlying collection.
838         */
839        public int size()
840        {
841          return c.size();
842        }
843    
844      } // class EnvironmentCollection<String>
845    
846      /**
847       * This is a specialised <code>HashMap</code>, which
848       * prevents the addition or querying of anything other than
849       * <code>String</code> objects. 
850       *
851       * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
852       */
853      static class EnvironmentMap
854        extends HashMap<String,String>
855      {
856        
857        /**
858         * Cache the entry set.
859         */
860        private transient Set<Map.Entry<String,String>> entries;
861    
862        /**
863         * Cache the key set.
864         */
865        private transient Set<String> keys;
866    
867        /**
868         * Cache the value collection.
869         */
870        private transient Collection<String> values;
871    
872        /**
873         * Constructs a new empty <code>EnvironmentMap</code>.
874         */
875        EnvironmentMap()
876        {
877          super();
878        }
879    
880        /**
881         * Constructs a new <code>EnvironmentMap</code> containing
882         * the contents of the specified map.
883         *
884         * @param m the map to be added to this.
885         * @throws NullPointerException if a key or value is null.
886         * @throws ClassCastException if a key or value is not a String.
887         */    
888        EnvironmentMap(Map<String,String> m)
889        {
890          super(m);
891        }
892    
893        /**
894         * Blocks queries containing a null key or one which is not
895         * of type <code>String</code>.  All other queries
896         * are forwarded to the superclass.
897         *
898         * @param key the key to look for in the map.
899         * @return true if the key exists in the map.
900         * @throws NullPointerException if the specified key is null.
901         */
902        public boolean containsKey(Object key)
903        {
904          if (key == null)
905            throw new
906              NullPointerException("This map does not support null keys.");
907          if (!(key instanceof String))
908            throw new
909              ClassCastException("This map only allows queries using Strings.");
910          return super.containsKey(key);
911        }
912        
913        /**
914         * Blocks queries using a null or non-<code>String</code> value.
915         * All other queries are forwarded to the superclass.
916         *
917         * @param value the value to look for in the map.
918         * @return true if the value exists in the map.
919         * @throws NullPointerException if the specified value is null.
920         */
921        public boolean containsValue(Object value)
922        {
923          if (value == null)
924              throw new
925                NullPointerException("This map does not support null values.");
926          if (!(value instanceof String))
927            throw new
928              ClassCastException("This map only allows queries using Strings.");
929          return super.containsValue(value);
930        }
931    
932        /**
933         * Returns a set view of the map entries, with the same
934         * provisions as for the underlying map.
935         *
936         * @return a set containing the map entries.
937         */
938        public Set<Map.Entry<String,String>> entrySet()
939        {
940          if (entries == null)
941            entries = super.entrySet();
942          return entries;
943        }
944    
945        /**
946         * Blocks queries containing a null or non-<code>String</code> key.
947         * All other queries are passed on to the superclass.
948         *
949         * @param key the key to retrieve the value for.
950         * @return the value associated with the given key.
951         * @throws NullPointerException if the specified key is null.
952         * @throws ClassCastException if the specified key is not a String.
953         */
954        public String get(Object key)
955        {
956          if (key == null)
957            throw new
958              NullPointerException("This map does not support null keys.");
959          if (!(key instanceof String))
960            throw new
961              ClassCastException("This map only allows queries using Strings.");
962          return super.get(key);
963        }
964        
965        /**
966         * Returns a set view of the keys, with the same
967         * provisions as for the underlying map.
968         *
969         * @return a set containing the keys.
970         */
971        public Set<String> keySet()
972        {
973          if (keys == null)
974            keys = new EnvironmentSet(super.keySet());
975          return keys;
976        }
977    
978        /**
979         * Associates the given key to the given value. If the
980         * map already contains the key, its value is replaced.
981         * The map does not accept null keys or values, or keys
982         * and values not of type {@link String}.
983         *
984         * @param key the key to map.
985         * @param value the value to be mapped.
986         * @return the previous value of the key, or null if there was no mapping
987         * @throws NullPointerException if a key or value is null.
988         * @throws ClassCastException if a key or value is not a String.
989         */
990        public String put(String key, String value)
991        {
992          if (key == null)
993            throw new NullPointerException("A new key is null.");
994          if (value == null)
995            throw new NullPointerException("A new value is null.");
996          if (!(key instanceof String))
997            throw new ClassCastException("A new key is not a String.");
998          if (!(value instanceof String))
999            throw new ClassCastException("A new value is not a String.");
1000          return super.put(key, value);
1001        }
1002    
1003        /**
1004         * Removes a key-value pair from the map.  The queried key may not
1005         * be null or of a type other than a <code>String</code>.
1006         *
1007         * @param key the key of the entry to remove.
1008         * @return the removed value.
1009         * @throws NullPointerException if the specified key is null.
1010         * @throws ClassCastException if the specified key is not a String.
1011         */
1012        public String remove(Object key)
1013        {
1014          if (key == null)
1015            throw new
1016              NullPointerException("This map does not support null keys.");
1017          if (!(key instanceof String))
1018            throw new
1019              ClassCastException("This map only allows queries using Strings.");
1020          return super.remove(key);
1021        }
1022        
1023        /**
1024         * Returns a collection view of the values, with the same
1025         * provisions as for the underlying map.
1026         *
1027         * @return a collection containing the values.
1028         */
1029        public Collection<String> values()
1030        {
1031          if (values == null)
1032            values = new EnvironmentCollection(super.values());
1033          return values;
1034        }
1035        
1036      }
1037    
1038      /**
1039       * This is a specialised <code>Set</code>, providing
1040       * the necessary provisions for the collections used by the
1041       * environment variable map.  Namely, it prevents
1042       * modifications and the use of queries with null
1043       * or non-<code>String</code> values.
1044       *
1045       * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
1046       */
1047      private static class EnvironmentSet
1048        extends EnvironmentCollection
1049        implements Set<String>
1050      {
1051    
1052        /**
1053         * Constructs a new environment set, which
1054         * wraps the elements of the supplied set.
1055         *
1056         * @param set the set to use as a base for
1057         *             this set.
1058         */
1059        public EnvironmentSet(Set<String> set)
1060        {
1061          super(set);
1062        }
1063    
1064        /**
1065         * This simply calls the same method on the wrapped
1066         * collection.
1067         *
1068         * @param obj the object to compare with.
1069         * @return true if the two objects are equal.
1070         */
1071        public boolean equals(Object obj)
1072        {
1073          return c.equals(obj);
1074        }
1075    
1076        /**
1077         * This simply calls the same method on the wrapped
1078         * collection.
1079         *
1080         * @return the hashcode of the collection.
1081         */
1082        public int hashCode()
1083        {
1084          return c.hashCode();
1085        }
1086    
1087      } // class EnvironmentSet<String>
1088    
1089    } // class System