- java.lang.Object
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- java.lang.System
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public final class System extends Object
TheSystemclass contains several useful class fields and methods. It cannot be instantiated. Among the facilities provided by theSystemclass 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
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Nested Class Summary
Nested Classes Modifier and Type Class Description static interfaceSystem.LoggerSystem.Loggerinstances log messages that will be routed to the underlying logging framework theLoggerFinderuses.static classSystem.LoggerFinderTheLoggerFinderservice is responsible for creating, managing, and configuring loggers to the underlying framework it uses.
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Field Summary
Fields Modifier and Type Field Description static PrintStreamerrThe "standard" error output stream.static InputStreaminThe "standard" input stream.static PrintStreamoutThe "standard" output stream.
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Method Summary
All Methods Static Methods Concrete Methods Modifier and Type Method Description static voidarraycopy(Object src, int srcPos, Object dest, int destPos, int length)Copies an array from the specified source array, beginning at the specified position, to the specified position of the destination array.static StringclearProperty(String key)Removes the system property indicated by the specified key.static Consoleconsole()Returns the uniqueConsoleobject associated with the current Java virtual machine, if any.static longcurrentTimeMillis()Returns the current time in milliseconds.static voidexit(int status)Terminates the currently running Java Virtual Machine.static voidgc()Runs the garbage collector.static Map<String,String>getenv()Returns an unmodifiable string map view of the current system environment.static Stringgetenv(String name)Gets the value of the specified environment variable.static System.LoggergetLogger(String name)Returns an instance ofLoggerfor the caller's use.static System.LoggergetLogger(String name, ResourceBundle bundle)Returns a localizable instance ofLoggerfor the caller's use.static PropertiesgetProperties()Determines the current system properties.static StringgetProperty(String key)Gets the system property indicated by the specified key.static StringgetProperty(String key, String def)Gets the system property indicated by the specified key.static SecurityManagergetSecurityManager()Gets the system security interface.static intidentityHashCode(Object x)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 ChannelinheritedChannel()Returns the channel inherited from the entity that created this Java virtual machine.static StringlineSeparator()Returns the system-dependent line separator string.static voidload(String filename)Loads the native library specified by the filename argument.static voidloadLibrary(String libname)Loads the native library specified by thelibnameargument.static StringmapLibraryName(String libname)Maps a library name into a platform-specific string representing a native library.static longnanoTime()Returns the current value of the running Java Virtual Machine's high-resolution time source, in nanoseconds.static voidrunFinalization()Runs the finalization methods of any objects pending finalization.static voidsetErr(PrintStream err)Reassigns the "standard" error output stream.static voidsetIn(InputStream in)Reassigns the "standard" input stream.static voidsetOut(PrintStream out)Reassigns the "standard" output stream.static voidsetProperties(Properties props)Sets the system properties to thePropertiesargument.static StringsetProperty(String key, String value)Sets the system property indicated by the specified key.static voidsetSecurityManager(SecurityManager s)Sets the System security.
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Field Detail
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in
public static final InputStream 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.
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out
public static final PrintStream 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.For simple stand-alone Java applications, a typical way to write a line of output data is:
System.out.println(data)See the
printlnmethods in classPrintStream.- See Also:
PrintStream.println(),PrintStream.println(boolean),PrintStream.println(char),PrintStream.println(char[]),PrintStream.println(double),PrintStream.println(float),PrintStream.println(int),PrintStream.println(long),PrintStream.println(java.lang.Object),PrintStream.println(java.lang.String)
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err
public static final PrintStream 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.
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Method Detail
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setIn
public static void setIn(InputStream in)
Reassigns the "standard" input stream. First, if there is a security manager, itscheckPermissionmethod 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 itscheckPermissionmethod doesn't allow reassigning of the standard input stream.- Since:
- 1.1
- See Also:
SecurityManager.checkPermission(java.security.Permission),RuntimePermission
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setOut
public static void setOut(PrintStream out)
Reassigns the "standard" output stream. First, if there is a security manager, itscheckPermissionmethod 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 itscheckPermissionmethod doesn't allow reassigning of the standard output stream.- Since:
- 1.1
- See Also:
SecurityManager.checkPermission(java.security.Permission),RuntimePermission
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setErr
public static void setErr(PrintStream err)
Reassigns the "standard" error output stream. First, if there is a security manager, itscheckPermissionmethod 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 itscheckPermissionmethod doesn't allow reassigning of the standard error output stream.- Since:
- 1.1
- See Also:
SecurityManager.checkPermission(java.security.Permission),RuntimePermission
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console
public static Console console()
Returns the uniqueConsoleobject associated with the current Java virtual machine, if any.- Returns:
- The system console, if any, otherwise
null. - Since:
- 1.6
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inheritedChannel
public static Channel inheritedChannel() throws IOException
Returns the channel inherited from the entity that created this Java virtual machine. This method returns the channel obtained by invoking theinheritedChannelmethod of the system-wide defaultSelectorProviderobject.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
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setSecurityManager
public static void setSecurityManager(SecurityManager s)
Sets the System security. If there is a security manager already installed, this method first calls the security manager'scheckPermissionmethod 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
nulland no security manager has been established, then no action is taken and the method simply returns.- Parameters:
s- the security manager.- Throws:
SecurityException- if the security manager has already been set and itscheckPermissionmethod doesn't allow it to be replaced.- See Also:
getSecurityManager(),SecurityManager.checkPermission(java.security.Permission),RuntimePermission
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getSecurityManager
public static SecurityManager getSecurityManager()
Gets the system security interface.- Returns:
- if a security manager has already been established for the
current application, then that security manager is returned;
otherwise,
nullis returned. - See Also:
setSecurityManager(java.lang.SecurityManager)
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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
Datefor 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:
Date
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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
instead ofif (System.nanoTime() - startTime >= timeoutNanos) ...
because of the possibility of numerical overflow.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
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arraycopy
public static void arraycopy(Object src, int srcPos, Object dest, int destPos, int length)
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 bysrcto the destination array referenced bydest. The number of components copied is equal to thelengthargument. The components at positionssrcPosthroughsrcPos+length-1in the source array are copied into positionsdestPosthroughdestPos+length-1, respectively, of the destination array.If the
srcanddestarguments refer to the same array object, then the copying is performed as if the components at positionssrcPosthroughsrcPos+length-1were first copied to a temporary array withlengthcomponents and then the contents of the temporary array were copied into positionsdestPosthroughdestPos+length-1of the destination array.If
destisnull, then aNullPointerExceptionis thrown.If
srcisnull, then aNullPointerExceptionis thrown and the destination array is not modified.Otherwise, if any of the following is true, an
ArrayStoreExceptionis thrown and the destination is not modified:- The
srcargument refers to an object that is not an array. - The
destargument refers to an object that is not an array. - The
srcargument anddestargument refer to arrays whose component types are different primitive types. - The
srcargument refers to an array with a primitive component type and thedestargument refers to an array with a reference component type. - The
srcargument refers to an array with a reference component type and thedestargument refers to an array with a primitive component type.
Otherwise, if any of the following is true, an
IndexOutOfBoundsExceptionis thrown and the destination is not modified:- The
srcPosargument is negative. - The
destPosargument is negative. - The
lengthargument is negative. srcPos+lengthis greater thansrc.length, the length of the source array.destPos+lengthis greater thandest.length, the length of the destination array.
Otherwise, if any actual component of the source array from position
srcPosthroughsrcPos+length-1cannot be converted to the component type of the destination array by assignment conversion, anArrayStoreExceptionis 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 positionssrcPosthroughsrcPos+k-1will already have been copied to destination array positionsdestPosthroughdestPos+k-1and 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 thesrcarray could not be stored into thedestarray because of a type mismatch.NullPointerException- if eithersrcordestisnull.
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identityHashCode
public static int identityHashCode(Object x)
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:
Object.hashCode(),Objects.hashCode(Object)
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getProperties
public static Properties getProperties()
Determines the current system properties. First, if there is a security manager, itscheckPropertiesAccessmethod 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 aPropertiesobject. If there is no current set of system properties, a set of system properties is first created and initialized. This set of system properties always includes values for the following keys:Key Description of Associated Value java.versionJava Runtime Environment version, which may be interpreted as a Runtime.Versionjava.version.dateJava Runtime Environment version date, in ISO-8601 YYYY-MM-DD format, which may be interpreted as a LocalDatejava.vendorJava Runtime Environment vendor java.vendor.urlJava vendor URL java.vendor.versionJava vendor version java.homeJava installation directory java.vm.specification.versionJava Virtual Machine specification version, whose value is the feature element of the runtime version java.vm.specification.vendorJava Virtual Machine specification vendor java.vm.specification.nameJava Virtual Machine specification name java.vm.versionJava Virtual Machine implementation version which may be interpreted as a Runtime.Versionjava.vm.vendorJava Virtual Machine implementation vendor java.vm.nameJava Virtual Machine implementation name java.specification.versionJava Runtime Environment specification version, whose value is the feature element of the runtime version java.specification.maintenance.versionJava Runtime Environment specification maintenance version, may be interpreted as a positive integer (optional, see below) java.specification.vendorJava Runtime Environment specification vendor java.specification.nameJava Runtime Environment specification name java.class.versionJava class format version number java.class.pathJava class path (refer to ClassLoader.getSystemClassLoader()for details)java.library.pathList of paths to search when loading libraries java.io.tmpdirDefault temp file path java.compilerName of JIT compiler to use os.nameOperating system name os.archOperating system architecture os.versionOperating system version file.separatorFile separator ("/" on UNIX) path.separatorPath separator (":" on UNIX) line.separatorLine separator ("\n" on UNIX) user.nameUser's account name user.homeUser's home directory user.dirUser's current working directory The
java.specification.maintenance.versionproperty 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
getPropertiesoperation, it may choose to permit thegetProperty(String)operation.- 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.pathThe application module path jdk.module.upgrade.pathThe upgrade module path jdk.module.mainThe module name of the initial/main module jdk.module.main.classThe main class name of the initial module - Returns:
- the system properties
- Throws:
SecurityException- if a security manager exists and itscheckPropertiesAccessmethod doesn't allow access to the system properties.- See Also:
setProperties(java.util.Properties),SecurityException,SecurityManager.checkPropertiesAccess(),Properties
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lineSeparator
public static String 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
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setProperties
public static void setProperties(Properties props)
Sets the system properties to thePropertiesargument. First, if there is a security manager, itscheckPropertiesAccessmethod 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 itscheckPropertiesAccessmethod doesn't allow access to the system properties.- See Also:
getProperties(),Properties,SecurityException,SecurityManager.checkPropertiesAccess()
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getProperty
public static String getProperty(String key)
Gets the system property indicated by the specified key. First, if there is a security manager, itscheckPropertyAccessmethod 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
getPropertiesmethod.- 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
nullif there is no property with that key. - Throws:
SecurityException- if a security manager exists and itscheckPropertyAccessmethod doesn't allow access to the specified system property.NullPointerException- ifkeyisnull.IllegalArgumentException- ifkeyis empty.- See Also:
setProperty(java.lang.String, java.lang.String),SecurityException,SecurityManager.checkPropertyAccess(java.lang.String),getProperties()
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getProperty
public static String getProperty(String key, String def)
Gets the system property indicated by the specified key. First, if there is a security manager, itscheckPropertyAccessmethod is called with thekeyas 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
getPropertiesmethod.- 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 itscheckPropertyAccessmethod doesn't allow access to the specified system property.NullPointerException- ifkeyisnull.IllegalArgumentException- ifkeyis empty.- See Also:
setProperty(java.lang.String, java.lang.String),SecurityManager.checkPropertyAccess(java.lang.String),getProperties()
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setProperty
public static String setProperty(String key, String value)
Sets the system property indicated by the specified key. First, if a security manager exists, itsSecurityManager.checkPermissionmethod 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
nullif it did not have one. - Throws:
SecurityException- if a security manager exists and itscheckPermissionmethod doesn't allow setting of the specified property.NullPointerException- ifkeyorvalueisnull.IllegalArgumentException- ifkeyis empty.- Since:
- 1.2
- See Also:
getProperty(java.lang.String),getProperty(java.lang.String),getProperty(java.lang.String, java.lang.String),PropertyPermission,SecurityManager.checkPermission(java.security.Permission)
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clearProperty
public static String clearProperty(String key)
Removes the system property indicated by the specified key. First, if a security manager exists, itsSecurityManager.checkPermissionmethod 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
nullif there was no property with that key. - Throws:
SecurityException- if a security manager exists and itscheckPropertyAccessmethod doesn't allow access to the specified system property.NullPointerException- ifkeyisnull.IllegalArgumentException- ifkeyis empty.- Since:
- 1.5
- See Also:
getProperty(java.lang.String),setProperty(java.lang.String, java.lang.String),Properties,SecurityException,SecurityManager.checkPropertiesAccess()
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getenv
public static String getenv(String name)
Gets the value of the specified environment variable. An environment variable is a system-dependent external named value.If a security manager exists, its
checkPermissionmethod is called with aRuntimePermission("getenv."+name)permission. This may result in aSecurityExceptionbeing thrown. If no exception is thrown the value of the variablenameis 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
nameis 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
nullif the variable is not defined in the system environment - Throws:
NullPointerException- ifnameisnullSecurityException- if a security manager exists and itscheckPermissionmethod doesn't allow access to the environment variablename- See Also:
getenv(),ProcessBuilder.environment()
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getenv
public static Map<String,String> 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 typeStringwill 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
checkPermissionmethod is called with aRuntimePermission("getenv.*")permission. This may result in aSecurityExceptionbeing 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 itscheckPermissionmethod doesn't allow access to the process environment- Since:
- 1.5
- See Also:
getenv(String),ProcessBuilder.environment()
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getLogger
public static System.Logger getLogger(String name)
Returns an instance ofLoggerfor the caller's use.- API Note:
- This method may defer calling the
LoggerFinder.getLoggermethod 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), wheremoduleis the caller's module. In cases whereSystem.getLoggeris called from a context where there is no caller frame on the stack (e.g when called directly from a JNI attached thread),IllegalCallerExceptionis thrown. To obtain a logger in such a context, use an auxiliary class that will implicitly be identified as the caller, or use the systemLoggerFinderto 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.Loggerthat can be used by the calling class. - Throws:
NullPointerException- ifnameisnull.IllegalCallerException- if there is no Java caller frame on the stack.- Since:
- 9
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getLogger
public static System.Logger getLogger(String name, ResourceBundle bundle)
Returns a localizable instance ofLoggerfor 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.LoggerFinderservice, 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), wheremoduleis the caller's module. In cases whereSystem.getLoggeris called from a context where there is no caller frame on the stack (e.g when called directly from a JNI attached thread),IllegalCallerExceptionis thrown. To obtain a logger in such a context, use an auxiliary class that will implicitly be identified as the caller, or use the systemLoggerFinderto 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.Loggerwhich will use the provided resource bundle for message localization. - Throws:
NullPointerException- ifnameisnullorbundleisnull.IllegalCallerException- if there is no Java caller frame on the stack.- Since:
- 9
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exit
public static void exit(int status)
Terminates the currently running Java Virtual Machine. The argument serves as a status code; by convention, a nonzero status code indicates abnormal termination.This method calls the
exitmethod in classRuntime. This method never returns normally.The call
System.exit(n)is effectively equivalent to the call:Runtime.getRuntime().exit(n)
- Parameters:
status- exit status.- Throws:
SecurityException- if a security manager exists and itscheckExitmethod doesn't allow exit with the specified status.- See Also:
Runtime.exit(int)
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gc
public static void gc()
Runs the garbage collector. Calling thegcmethod suggests that the Java Virtual Machine expend effort toward recycling unused objects in order to make the memory they currently occupy available for quick reuse. When control returns from the method call, the Java Virtual Machine has made a best effort to reclaim space from all discarded objects.The call
System.gc()is effectively equivalent to the call:Runtime.getRuntime().gc()
- See Also:
Runtime.gc()
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runFinalization
public static void runFinalization()
Runs the finalization methods of any objects pending finalization. Calling this method suggests that the Java Virtual Machine expend effort toward running thefinalizemethods of objects that have been found to be discarded but whosefinalizemethods 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 Also:
Runtime.runFinalization()
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load
public static void load(String filename)
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 itscheckLinkmethod 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- iffilenameisnull- See Also:
Runtime.load(java.lang.String),SecurityManager.checkLink(java.lang.String)
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loadLibrary
public static void loadLibrary(String libname)
Loads the native library specified by thelibnameargument. Thelibnameargument must not contain any platform specific prefix, file extension or path. If a native library calledlibnameis statically linked with the VM, then the JNI_OnLoad_libnamefunction 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 itscheckLinkmethod 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- iflibnameisnull- See Also:
Runtime.loadLibrary(java.lang.String),SecurityManager.checkLink(java.lang.String)
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mapLibraryName
public static String mapLibraryName(String libname)
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- iflibnameisnull- Since:
- 1.2
- See Also:
loadLibrary(java.lang.String),ClassLoader.findLibrary(java.lang.String)
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