Class System
System
class contains several useful class fields
and methods. It cannot be instantiated.
Among the facilities provided by the System
class
are standard input, standard output, and error output streams;
access to externally defined properties and environment
variables; a means of loading files and libraries; and a utility
method for quickly copying a portion of an array.- Since:
- 1.0
-
Nested Class Summary
Modifier and TypeClassDescriptionstatic interface
System.Logger
instances log messages that will be routed to the underlying logging framework theLoggerFinder
uses.static class
TheLoggerFinder
service is responsible for creating, managing, and configuring loggers to the underlying framework it uses. -
Field Summary
Modifier and TypeFieldDescriptionstatic final PrintStream
The "standard" error output stream.static final InputStream
The "standard" input stream.static final PrintStream
The "standard" output stream. -
Method Summary
Modifier and TypeMethodDescriptionstatic void
Copies an array from the specified source array, beginning at the specified position, to the specified position of the destination array.static String
clearProperty
(String key) Removes the system property indicated by the specified key.static Console
console()
Returns the uniqueConsole
object associated with the current Java virtual machine, if any.static long
Returns the current time in milliseconds.static void
exit
(int status) Initiates the shutdown sequence of the Java Virtual Machine.static void
gc()
Runs the garbage collector in the Java Virtual Machine.getenv()
Returns an unmodifiable string map view of the current system environment.static String
Gets the value of the specified environment variable.static System.Logger
Returns an instance ofLogger
for the caller's use.static System.Logger
getLogger
(String name, ResourceBundle bundle) Returns a localizable instance ofLogger
for the caller's use.static Properties
Determines the current system properties.static String
getProperty
(String key) Gets the system property indicated by the specified key.static String
getProperty
(String key, String def) Gets the system property indicated by the specified key.static SecurityManager
Deprecated, for removal: This API element is subject to removal in a future version.This method is only useful in conjunction with the Security Manager, which is deprecated and subject to removal in a future release.static int
Returns the same hash code for the given object as would be returned by the default method hashCode(), whether or not the given object's class overrides hashCode().static Channel
Returns the channel inherited from the entity that created this Java virtual machine.static String
Returns the system-dependent line separator string.static void
Restricted.Loads the native library specified by the filename argument.static void
loadLibrary
(String libname) Restricted.Loads the native library specified by thelibname
argument.static String
mapLibraryName
(String libname) Maps a library name into a platform-specific string representing a native library.static long
nanoTime()
Returns the current value of the running Java Virtual Machine's high-resolution time source, in nanoseconds.static void
Deprecated, for removal: This API element is subject to removal in a future version.Finalization has been deprecated for removal.static void
setErr
(PrintStream err) Reassigns the "standard" error output stream.static void
setIn
(InputStream in) Reassigns the "standard" input stream.static void
setOut
(PrintStream out) Reassigns the "standard" output stream.static void
setProperties
(Properties props) Sets the system properties to theProperties
argument.static String
setProperty
(String key, String value) Sets the system property indicated by the specified key.static void
Deprecated, for removal: This API element is subject to removal in a future version.This method is only useful in conjunction with the Security Manager, which is deprecated and subject to removal in a future release.
-
Field Details
-
in
The "standard" input stream. This stream is already open and ready to supply input data. Typically this stream corresponds to keyboard input or another input source specified by the host environment or user. In case this stream is wrapped in aInputStreamReader
,Console.charset()
should be used for the charset, or consider usingConsole.reader()
.- See Also:
-
out
The "standard" output stream. This stream is already open and ready to accept output data. Typically this stream corresponds to display output or another output destination specified by the host environment or user. The encoding used in the conversion from characters to bytes is equivalent toConsole.charset()
if theConsole
exists, stdout.encoding otherwise.For simple stand-alone Java applications, a typical way to write a line of output data is:
System.out.println(data)
See the
println
methods in classPrintStream
.- See Also:
-
err
The "standard" error output stream. This stream is already open and ready to accept output data.Typically this stream corresponds to display output or another output destination specified by the host environment or user. By convention, this output stream is used to display error messages or other information that should come to the immediate attention of a user even if the principal output stream, the value of the variable
out
, has been redirected to a file or other destination that is typically not continuously monitored. The encoding used in the conversion from characters to bytes is equivalent toConsole.charset()
if theConsole
exists, stderr.encoding otherwise.- See Also:
-
-
Method Details
-
setIn
Reassigns the "standard" input stream. First, if there is a security manager, itscheckPermission
method is called with aRuntimePermission("setIO")
permission to see if it's ok to reassign the "standard" input stream.- Parameters:
in
- the new standard input stream.- Throws:
SecurityException
- if a security manager exists and itscheckPermission
method doesn't allow reassigning of the standard input stream.- Since:
- 1.1
- See Also:
-
setOut
Reassigns the "standard" output stream. First, if there is a security manager, itscheckPermission
method is called with aRuntimePermission("setIO")
permission to see if it's ok to reassign the "standard" output stream.- Parameters:
out
- the new standard output stream- Throws:
SecurityException
- if a security manager exists and itscheckPermission
method doesn't allow reassigning of the standard output stream.- Since:
- 1.1
- See Also:
-
setErr
Reassigns the "standard" error output stream. First, if there is a security manager, itscheckPermission
method is called with aRuntimePermission("setIO")
permission to see if it's ok to reassign the "standard" error output stream.- Parameters:
err
- the new standard error output stream.- Throws:
SecurityException
- if a security manager exists and itscheckPermission
method doesn't allow reassigning of the standard error output stream.- Since:
- 1.1
- See Also:
-
console
-
inheritedChannel
Returns the channel inherited from the entity that created this Java virtual machine. This method returns the channel obtained by invoking theinheritedChannel
method of the system-wide defaultSelectorProvider
object.In addition to the network-oriented channels described in
inheritedChannel
, this method may return other kinds of channels in the future.- Returns:
- The inherited channel, if any, otherwise
null
. - Throws:
IOException
- If an I/O error occursSecurityException
- If a security manager is present and it does not permit access to the channel.- Since:
- 1.5
-
setSecurityManager
Deprecated, for removal: This API element is subject to removal in a future version.This method is only useful in conjunction with the Security Manager, which is deprecated and subject to removal in a future release. Consequently, this method is also deprecated and subject to removal. There is no replacement for the Security Manager or this method.Sets the system-wide security manager. If there is a security manager already installed, this method first calls the security manager'scheckPermission
method with aRuntimePermission("setSecurityManager")
permission to ensure it's ok to replace the existing security manager. This may result in throwing aSecurityException
.Otherwise, the argument is established as the current security manager. If the argument is
null
and no security manager has been established, then no action is taken and the method simply returns.- Implementation Note:
- In the JDK implementation, if the Java virtual machine is
started with the system property
java.security.manager
not set or set to the special token "disallow
" then thesetSecurityManager
method cannot be used to set a security manager. See the following section of theSecurityManager
class specification for more details. - Parameters:
sm
- the security manager ornull
- Throws:
SecurityException
- if the security manager has already been set and itscheckPermission
method doesn't allow it to be replacedUnsupportedOperationException
- ifsm
is non-null and a security manager is not allowed to be set dynamically- See Also:
-
getSecurityManager
Deprecated, for removal: This API element is subject to removal in a future version.This method is only useful in conjunction with the Security Manager, which is deprecated and subject to removal in a future release. Consequently, this method is also deprecated and subject to removal. There is no replacement for the Security Manager or this method.Gets the system-wide security manager.- Returns:
- if a security manager has already been established for the
current application, then that security manager is returned;
otherwise,
null
is returned. - See Also:
-
currentTimeMillis
public static long currentTimeMillis()Returns the current time in milliseconds. Note that while the unit of time of the return value is a millisecond, the granularity of the value depends on the underlying operating system and may be larger. For example, many operating systems measure time in units of tens of milliseconds.See the description of the class
Date
for a discussion of slight discrepancies that may arise between "computer time" and coordinated universal time (UTC).- Returns:
- the difference, measured in milliseconds, between the current time and midnight, January 1, 1970 UTC.
- See Also:
-
nanoTime
public static long nanoTime()Returns the current value of the running Java Virtual Machine's high-resolution time source, in nanoseconds. This method can only be used to measure elapsed time and is not related to any other notion of system or wall-clock time. The value returned represents nanoseconds since some fixed but arbitrary origin time (perhaps in the future, so values may be negative). The same origin is used by all invocations of this method in an instance of a Java virtual machine; other virtual machine instances are likely to use a different origin.This method provides nanosecond precision, but not necessarily nanosecond resolution (that is, how frequently the value changes) - no guarantees are made except that the resolution is at least as good as that of
currentTimeMillis()
.Differences in successive calls that span greater than approximately 292 years (263 nanoseconds) will not correctly compute elapsed time due to numerical overflow.
The values returned by this method become meaningful only when the difference between two such values, obtained within the same instance of a Java virtual machine, is computed.
For example, to measure how long some code takes to execute:
long startTime = System.nanoTime(); // ... the code being measured ... long elapsedNanos = System.nanoTime() - startTime;
To compare elapsed time against a timeout, use
if (System.nanoTime() - startTime >= timeoutNanos) ...
if (System.nanoTime() >= startTime + timeoutNanos) ...
- Returns:
- the current value of the running Java Virtual Machine's high-resolution time source, in nanoseconds
- Since:
- 1.5
-
arraycopy
Copies an array from the specified source array, beginning at the specified position, to the specified position of the destination array. A subsequence of array components are copied from the source array referenced bysrc
to the destination array referenced bydest
. The number of components copied is equal to thelength
argument. The components at positionssrcPos
throughsrcPos+length-1
in the source array are copied into positionsdestPos
throughdestPos+length-1
, respectively, of the destination array.If the
src
anddest
arguments refer to the same array object, then the copying is performed as if the components at positionssrcPos
throughsrcPos+length-1
were first copied to a temporary array withlength
components and then the contents of the temporary array were copied into positionsdestPos
throughdestPos+length-1
of the destination array.If
dest
isnull
, then aNullPointerException
is thrown.If
src
isnull
, then aNullPointerException
is thrown and the destination array is not modified.Otherwise, if any of the following is true, an
ArrayStoreException
is thrown and the destination is not modified:- The
src
argument refers to an object that is not an array. - The
dest
argument refers to an object that is not an array. - The
src
argument anddest
argument refer to arrays whose component types are different primitive types. - The
src
argument refers to an array with a primitive component type and thedest
argument refers to an array with a reference component type. - The
src
argument refers to an array with a reference component type and thedest
argument refers to an array with a primitive component type.
Otherwise, if any of the following is true, an
IndexOutOfBoundsException
is thrown and the destination is not modified:- The
srcPos
argument is negative. - The
destPos
argument is negative. - The
length
argument is negative. srcPos+length
is greater thansrc.length
, the length of the source array.destPos+length
is greater thandest.length
, the length of the destination array.
Otherwise, if any actual component of the source array from position
srcPos
throughsrcPos+length-1
cannot be converted to the component type of the destination array by assignment conversion, anArrayStoreException
is thrown. In this case, let k be the smallest nonnegative integer less than length such thatsrc[srcPos+
k]
cannot be converted to the component type of the destination array; when the exception is thrown, source array components from positionssrcPos
throughsrcPos+
k-1
will already have been copied to destination array positionsdestPos
throughdestPos+
k-1
and no other positions of the destination array will have been modified. (Because of the restrictions already itemized, this paragraph effectively applies only to the situation where both arrays have component types that are reference types.)- Parameters:
src
- the source array.srcPos
- starting position in the source array.dest
- the destination array.destPos
- starting position in the destination data.length
- the number of array elements to be copied.- Throws:
IndexOutOfBoundsException
- if copying would cause access of data outside array bounds.ArrayStoreException
- if an element in thesrc
array could not be stored into thedest
array because of a type mismatch.NullPointerException
- if eithersrc
ordest
isnull
.
- The
-
identityHashCode
Returns the same hash code for the given object as would be returned by the default method hashCode(), whether or not the given object's class overrides hashCode(). The hash code for the null reference is zero.- Parameters:
x
- object for which the hashCode is to be calculated- Returns:
- the hashCode
- Since:
- 1.1
- See Also:
-
getProperties
Determines the current system properties. First, if there is a security manager, itscheckPropertiesAccess
method is called with no arguments. This may result in a security exception.The current set of system properties for use by the
getProperty(String)
method is returned as aProperties
object. If there is no current set of system properties, a set of system properties is first created and initialized. This set of system properties includes a value for each of the following keys unless the description of the associated value indicates that the value is optional.Key Description of Associated Value java.version
Java Runtime Environment version, which may be interpreted as a Runtime.Version
java.version.date
Java Runtime Environment version date, in ISO-8601 YYYY-MM-DD format, which may be interpreted as a LocalDate
java.vendor
Java Runtime Environment vendor java.vendor.url
Java vendor URL java.vendor.version
Java vendor version (optional) java.home
Java installation directory java.vm.specification.version
Java Virtual Machine specification version, whose value is the feature element of the runtime version java.vm.specification.vendor
Java Virtual Machine specification vendor java.vm.specification.name
Java Virtual Machine specification name java.vm.version
Java Virtual Machine implementation version which may be interpreted as a Runtime.Version
java.vm.vendor
Java Virtual Machine implementation vendor java.vm.name
Java Virtual Machine implementation name java.specification.version
Java Runtime Environment specification version, whose value is the feature element of the runtime version java.specification.maintenance.version
Java Runtime Environment specification maintenance version, may be interpreted as a positive integer (optional, see below) java.specification.vendor
Java Runtime Environment specification vendor java.specification.name
Java Runtime Environment specification name java.class.version
Latest Java class file format version recognized by the Java runtime as "MAJOR.MINOR"
whereMAJOR
andMINOR
are both formatted as decimal integersjava.class.path
Java class path (refer to ClassLoader.getSystemClassLoader()
for details)java.library.path
List of paths to search when loading libraries java.io.tmpdir
Default temp file path os.name
Operating system name os.arch
Operating system architecture os.version
Operating system version file.separator
File separator ("/" on UNIX) path.separator
Path separator (":" on UNIX) line.separator
Line separator ("\n" on UNIX) user.name
User's account name user.home
User's home directory user.dir
User's current working directory native.encoding
Character encoding name derived from the host environment and/or the user's settings. Setting this system property has no effect. stdout.encoding
Character encoding name for System.out
. The Java runtime can be started with the system property set toUTF-8
, starting it with the property set to another value leads to undefined behavior.stderr.encoding
Character encoding name for System.err
. The Java runtime can be started with the system property set toUTF-8
, starting it with the property set to another value leads to undefined behavior.The
java.specification.maintenance.version
property is defined if the specification implemented by this runtime at the time of its construction had undergone a maintenance release. When defined, its value identifies that maintenance release. To indicate the first maintenance release this property will have the value"1"
, to indicate the second maintenance release this property will have the value"2"
, and so on.Multiple paths in a system property value are separated by the path separator character of the platform.
Note that even if the security manager does not permit the
getProperties
operation, it may choose to permit thegetProperty(String)
operation.Additional locale-related system properties defined by the
Default Locale
section in theLocale
class description may also be obtained with this method.- API Note:
- Changing a standard system property may have unpredictable results
unless otherwise specified.
Property values may be cached during initialization or on first use.
Setting a standard property after initialization using
getProperties()
,setProperties(Properties)
,setProperty(String, String)
, orclearProperty(String)
may not have the desired effect. - Implementation Note:
- In addition to the standard system properties, the system
properties may include the following keys:
Key Description of Associated Value jdk.module.path
The application module path jdk.module.upgrade.path
The upgrade module path jdk.module.main
The module name of the initial/main module jdk.module.main.class
The main class name of the initial module file.encoding
The name of the default charset, defaults to UTF-8
. The property may be set on the command line to the valueUTF-8
orCOMPAT
. If set on the command line to the valueCOMPAT
then the value is replaced with the value of thenative.encoding
property during startup. Setting the property to a value other thanUTF-8
orCOMPAT
leads to unspecified behavior. - Returns:
- the system properties
- Throws:
SecurityException
- if a security manager exists and itscheckPropertiesAccess
method doesn't allow access to the system properties.- See Also:
-
lineSeparator
Returns the system-dependent line separator string. It always returns the same value - the initial value of the system propertyline.separator
.On UNIX systems, it returns
"\n"
; on Microsoft Windows systems it returns"\r\n"
.- Returns:
- the system-dependent line separator string
- Since:
- 1.7
-
setProperties
Sets the system properties to theProperties
argument. First, if there is a security manager, itscheckPropertiesAccess
method is called with no arguments. This may result in a security exception.The argument becomes the current set of system properties for use by the
getProperty(String)
method. If the argument isnull
, then the current set of system properties is forgotten.- API Note:
- Changing a standard system property may have unpredictable results unless otherwise specified. See getProperties for details.
- Parameters:
props
- the new system properties.- Throws:
SecurityException
- if a security manager exists and itscheckPropertiesAccess
method doesn't allow access to the system properties.- See Also:
-
getProperty
Gets the system property indicated by the specified key. First, if there is a security manager, itscheckPropertyAccess
method is called with the key as its argument. This may result in a SecurityException.If there is no current set of system properties, a set of system properties is first created and initialized in the same manner as for the
getProperties
method.- API Note:
- Changing a standard system property may have unpredictable results unless otherwise specified. See getProperties for details.
- Parameters:
key
- the name of the system property.- Returns:
- the string value of the system property,
or
null
if there is no property with that key. - Throws:
SecurityException
- if a security manager exists and itscheckPropertyAccess
method doesn't allow access to the specified system property.NullPointerException
- ifkey
isnull
.IllegalArgumentException
- ifkey
is empty.- See Also:
-
getProperty
Gets the system property indicated by the specified key. First, if there is a security manager, itscheckPropertyAccess
method is called with thekey
as its argument.If there is no current set of system properties, a set of system properties is first created and initialized in the same manner as for the
getProperties
method.- Parameters:
key
- the name of the system property.def
- a default value.- Returns:
- the string value of the system property, or the default value if there is no property with that key.
- Throws:
SecurityException
- if a security manager exists and itscheckPropertyAccess
method doesn't allow access to the specified system property.NullPointerException
- ifkey
isnull
.IllegalArgumentException
- ifkey
is empty.- See Also:
-
setProperty
Sets the system property indicated by the specified key. First, if a security manager exists, itsSecurityManager.checkPermission
method is called with aPropertyPermission(key, "write")
permission. This may result in a SecurityException being thrown. If no exception is thrown, the specified property is set to the given value.- API Note:
- Changing a standard system property may have unpredictable results unless otherwise specified. See getProperties for details.
- Parameters:
key
- the name of the system property.value
- the value of the system property.- Returns:
- the previous value of the system property,
or
null
if it did not have one. - Throws:
SecurityException
- if a security manager exists and itscheckPermission
method doesn't allow setting of the specified property.NullPointerException
- ifkey
orvalue
isnull
.IllegalArgumentException
- ifkey
is empty.- Since:
- 1.2
- See Also:
-
clearProperty
Removes the system property indicated by the specified key. First, if a security manager exists, itsSecurityManager.checkPermission
method is called with aPropertyPermission(key, "write")
permission. This may result in a SecurityException being thrown. If no exception is thrown, the specified property is removed.- API Note:
- Changing a standard system property may have unpredictable results unless otherwise specified. See getProperties method for details.
- Parameters:
key
- the name of the system property to be removed.- Returns:
- the previous string value of the system property,
or
null
if there was no property with that key. - Throws:
SecurityException
- if a security manager exists and itscheckPropertyAccess
method doesn't allow access to the specified system property.NullPointerException
- ifkey
isnull
.IllegalArgumentException
- ifkey
is empty.- Since:
- 1.5
- See Also:
-
getenv
Gets the value of the specified environment variable. An environment variable is a system-dependent external named value.If a security manager exists, its
checkPermission
method is called with aRuntimePermission("getenv."+name)
permission. This may result in aSecurityException
being thrown. If no exception is thrown the value of the variablename
is returned.System properties and environment variables are both conceptually mappings between names and values. Both mechanisms can be used to pass user-defined information to a Java process. Environment variables have a more global effect, because they are visible to all descendants of the process which defines them, not just the immediate Java subprocess. They can have subtly different semantics, such as case insensitivity, on different operating systems. For these reasons, environment variables are more likely to have unintended side effects. It is best to use system properties where possible. Environment variables should be used when a global effect is desired, or when an external system interface requires an environment variable (such as
PATH
).On UNIX systems the alphabetic case of
name
is typically significant, while on Microsoft Windows systems it is typically not. For example, the expressionSystem.getenv("FOO").equals(System.getenv("foo"))
is likely to be true on Microsoft Windows.- Parameters:
name
- the name of the environment variable- Returns:
- the string value of the variable, or
null
if the variable is not defined in the system environment - Throws:
NullPointerException
- ifname
isnull
SecurityException
- if a security manager exists and itscheckPermission
method doesn't allow access to the environment variablename
- See Also:
-
getenv
Returns an unmodifiable string map view of the current system environment. The environment is a system-dependent mapping from names to values which is passed from parent to child processes.If the system does not support environment variables, an empty map is returned.
The returned map will never contain null keys or values. Attempting to query the presence of a null key or value will throw a
NullPointerException
. Attempting to query the presence of a key or value which is not of typeString
will throw aClassCastException
.The returned map and its collection views may not obey the general contract of the
Object.equals(java.lang.Object)
andObject.hashCode()
methods.The returned map is typically case-sensitive on all platforms.
If a security manager exists, its
checkPermission
method is called with aRuntimePermission("getenv.*")
permission. This may result in aSecurityException
being thrown.When passing information to a Java subprocess, system properties are generally preferred over environment variables.
- Returns:
- the environment as a map of variable names to values
- Throws:
SecurityException
- if a security manager exists and itscheckPermission
method doesn't allow access to the process environment- Since:
- 1.5
- See Also:
-
getLogger
Returns an instance ofLogger
for the caller's use.- API Note:
- This method may defer calling the
LoggerFinder.getLogger
method to create an actual logger supplied by the logging backend, for instance, to allow loggers to be obtained during the system initialization time. - Implementation Requirements:
- Instances returned by this method route messages to loggers
obtained by calling
LoggerFinder.getLogger(name, module)
, wheremodule
is the caller's module. In cases whereSystem.getLogger
is called from a context where there is no caller frame on the stack (e.g when called directly from a JNI attached thread),IllegalCallerException
is thrown. To obtain a logger in such a context, use an auxiliary class that will implicitly be identified as the caller, or use the systemLoggerFinder
to obtain a logger instead. Note that doing the latter may eagerly initialize the underlying logging system. - Parameters:
name
- the name of the logger.- Returns:
- an instance of
System.Logger
that can be used by the calling class. - Throws:
NullPointerException
- ifname
isnull
.IllegalCallerException
- if there is no Java caller frame on the stack.- Since:
- 9
-
getLogger
Returns a localizable instance ofLogger
for the caller's use. The returned logger will use the provided resource bundle for message localization.- API Note:
- This method is intended to be used after the system is fully initialized.
This method may trigger the immediate loading and initialization
of the
System.LoggerFinder
service, which may cause issues if the Java Runtime is not ready to initialize the concrete service implementation yet. System classes which may be loaded early in the boot sequence and need to log localized messages should create a logger usinggetLogger(java.lang.String)
and then use the log methods that take a resource bundle as parameter. - Implementation Requirements:
- The returned logger will perform message localization as specified
by
LoggerFinder.getLocalizedLogger(name, bundle, module)
, wheremodule
is the caller's module. In cases whereSystem.getLogger
is called from a context where there is no caller frame on the stack (e.g when called directly from a JNI attached thread),IllegalCallerException
is thrown. To obtain a logger in such a context, use an auxiliary class that will implicitly be identified as the caller, or use the systemLoggerFinder
to obtain a logger instead. Note that doing the latter may eagerly initialize the underlying logging system. - Parameters:
name
- the name of the logger.bundle
- a resource bundle.- Returns:
- an instance of
System.Logger
which will use the provided resource bundle for message localization. - Throws:
NullPointerException
- ifname
isnull
orbundle
isnull
.IllegalCallerException
- if there is no Java caller frame on the stack.- Since:
- 9
-
exit
public static void exit(int status) Initiates the shutdown sequence of the Java Virtual Machine. Unless the security manager denies exiting, this method initiates the shutdown sequence (if it is not already initiated) and then blocks indefinitely. This method neither returns nor throws an exception; that is, it does not complete either normally or abruptly.The argument serves as a status code. By convention, a nonzero status code indicates abnormal termination.
The call
System.exit(n)
is effectively equivalent to the call:Runtime.getRuntime().exit(n)
- Implementation Note:
- The initiation of the shutdown sequence is logged by
Runtime.exit(int)
. - Parameters:
status
- exit status.- Throws:
SecurityException
- if a security manager exists and itscheckExit
method doesn't allow exit with the specified status.- See Also:
-
gc
public static void gc()Runs the garbage collector in the Java Virtual Machine.Calling the
gc
method suggests that the Java Virtual Machine expend effort toward recycling unused objects in order to make the memory they currently occupy available for reuse by the Java Virtual Machine. When control returns from the method call, the Java Virtual Machine has made a best effort to reclaim space from all unused objects. There is no guarantee that this effort will recycle any particular number of unused objects, reclaim any particular amount of space, or complete at any particular time, if at all, before the method returns or ever. There is also no guarantee that this effort will determine the change of reachability in any particular number of objects, or that any particular number ofReference
objects will be cleared and enqueued.The call
System.gc()
is effectively equivalent to the call:Runtime.getRuntime().gc()
- See Also:
-
runFinalization
Deprecated, for removal: This API element is subject to removal in a future version.Finalization has been deprecated for removal. SeeObject.finalize()
for background information and details about migration options.When running in a JVM in which finalization has been disabled or removed, no objects will be pending finalization, so this method does nothing.
Runs the finalization methods of any objects pending finalization. Calling this method suggests that the Java Virtual Machine expend effort toward running thefinalize
methods of objects that have been found to be discarded but whosefinalize
methods have not yet been run. When control returns from the method call, the Java Virtual Machine has made a best effort to complete all outstanding finalizations.The call
System.runFinalization()
is effectively equivalent to the call:Runtime.getRuntime().runFinalization()
- See Java Language Specification:
-
12.6 Finalization of Class Instances
- See Also:
-
load
load
is a restricted method of the Java platform.Programs can only useload
when access to restricted methods is enabled.Restricted methods are unsafe, and, if used incorrectly, might crash the JVM or result in memory corruption.Loads the native library specified by the filename argument. The filename argument must be an absolute path name. If the filename argument, when stripped of any platform-specific library prefix, path, and file extension, indicates a library whose name is, for example, L, and a native library called L is statically linked with the VM, then the JNI_OnLoad_L function exported by the library is invoked rather than attempting to load a dynamic library. A filename matching the argument does not have to exist in the file system. See the JNI Specification for more details. Otherwise, the filename argument is mapped to a native library image in an implementation-dependent manner.The call
System.load(name)
is effectively equivalent to the call:Runtime.getRuntime().load(name)
- Parameters:
filename
- the file to load.- Throws:
SecurityException
- if a security manager exists and itscheckLink
method doesn't allow loading of the specified dynamic libraryUnsatisfiedLinkError
- if either the filename is not an absolute path name, the native library is not statically linked with the VM, or the library cannot be mapped to a native library image by the host system.NullPointerException
- iffilename
isnull
IllegalCallerException
- if the caller is in a module that does not have native access enabled.- External Specifications
- See Also:
-
loadLibrary
loadLibrary
is a restricted method of the Java platform.Programs can only useloadLibrary
when access to restricted methods is enabled.Restricted methods are unsafe, and, if used incorrectly, might crash the JVM or result in memory corruption.Loads the native library specified by thelibname
argument. Thelibname
argument must not contain any platform specific prefix, file extension or path. If a native library calledlibname
is statically linked with the VM, then the JNI_OnLoad_libname
function exported by the library is invoked. See the JNI Specification for more details. Otherwise, the libname argument is loaded from a system library location and mapped to a native library image in an implementation-dependent manner.The call
System.loadLibrary(name)
is effectively equivalent to the callRuntime.getRuntime().loadLibrary(name)
- Parameters:
libname
- the name of the library.- Throws:
SecurityException
- if a security manager exists and itscheckLink
method doesn't allow loading of the specified dynamic libraryUnsatisfiedLinkError
- if either the libname argument contains a file path, the native library is not statically linked with the VM, or the library cannot be mapped to a native library image by the host system.NullPointerException
- iflibname
isnull
IllegalCallerException
- if the caller is in a module that does not have native access enabled.- External Specifications
- See Also:
-
mapLibraryName
Maps a library name into a platform-specific string representing a native library.- Parameters:
libname
- the name of the library.- Returns:
- a platform-dependent native library name.
- Throws:
NullPointerException
- iflibname
isnull
- Since:
- 1.2
- See Also:
-