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| java.lang.Object
 java.lang.System
| System | | final public class System (Code) | | The 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.
author:
unascribed
version:
1.165, 06/11/07
since:
JDK1.0 |
| Field Summary | |
| final public static PrintStream | err
The "standard" error output stream. | | final public static InputStream | in
The "standard" input stream. | | final public static PrintStream | out
The "standard" output stream. |
| Method Summary | |
| native 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 by src to the destination array
referenced by dest. | | public static String | clearProperty(String key)
Removes the system property indicated by the specified key.
First, if a security manager exists, its
SecurityManager.checkPermission method
is called with a PropertyPermission(key, "write")
permission. | | public static Console | console()
Returns the unique
java.io.Console Console object associated
with the current Java virtual machine, if any. | | native public static long | currentTimeMillis()
Returns the current time in milliseconds. | | public static void | exit(int status)
Terminates the currently running Java Virtual Machine. | | public static void | gc()
Runs the garbage collector. | | static Class | getCallerClass()
| | public static Properties | getProperties()
Determines the current system properties.
First, if there is a security manager, its
checkPropertiesAccess method is called with no
arguments. | | public static String | getProperty(String key)
Gets the system property indicated by the specified key.
First, if there is a security manager, its
checkPropertyAccess method is called with the key as
its argument. | | public static String | getProperty(String key, String def)
Gets the system property indicated by the specified key.
First, if there is a security manager, its
checkPropertyAccess method is called with the
key 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.
Parameters:
def - a default value. | | public static SecurityManager | getSecurityManager()
Gets the system security interface. | | public static String | getenv(String name)
Gets the value of the specified environment variable. | | public static java.util.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 . | | native 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(). | | public static Channel | inheritedChannel()
Returns the channel inherited from the entity that created this
Java virtual machine.
This method returns the channel obtained by invoking the
java.nio.channels.spi.SelectorProvider.inheritedChannelinheritedChannel method of the system-wide default
java.nio.channels.spi.SelectorProvider object. | | public static void | load(String filename)
Loads a code file with the specified filename from the local file
system as a dynamic library. | | public static void | loadLibrary(String libname)
Loads the system library specified by the libname
argument. | | native 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. | | native 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). | | 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 the finalize methods of objects
that have been found to be discarded but whose finalize
methods have not yet been run. | | public static void | runFinalizersOnExit(boolean value)
Enable or disable finalization on exit; doing so specifies that the
finalizers of all objects that have finalizers that have not yet been
automatically invoked are to be run before the Java runtime exits. | | public static void | setErr(PrintStream err)
Reassigns the "standard" error output stream. | | public static void | setIn(InputStream in)
Reassigns the "standard" input stream. | | public static void | setOut(PrintStream out)
Reassigns the "standard" output stream. | | public static void | setProperties(Properties props)
Sets the system properties to the Properties
argument.
First, if there is a security manager, its
checkPropertiesAccess method is called with no
arguments. | | public static String | setProperty(String key, String value)
Sets the system property indicated by the specified key.
First, if a security manager exists, its
SecurityManager.checkPermission method
is called with a PropertyPermission(key, "write")
permission. | | 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's checkPermission method
with a RuntimePermission("setSecurityManager")
permission to ensure it's ok to replace the existing
security manager.
This may result in throwing a SecurityException.
Otherwise, the argument is established as the current
security manager. |
| err | | final public static PrintStream err(Code) | | 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.
|
| in | | final public static InputStream in(Code) | | 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.
|
| arraycopy | | native public static void arraycopy(Object src, int srcPos, Object dest, int destPos, int length)(Code) | | 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 by src to the destination array
referenced by dest. The number of components copied is
equal to the length argument. The components at
positions srcPos through
srcPos+length-1 in the source array are copied into
positions destPos through
destPos+length-1, respectively, of the destination
array.
If the src and dest arguments refer to the
same array object, then the copying is performed as if the
components at positions srcPos through
srcPos+length-1 were first copied to a temporary
array with length components and then the contents of
the temporary array were copied into positions
destPos through destPos+length-1 of the
destination array.
If dest is null, then a
NullPointerException is thrown.
If src is null, then a
NullPointerException 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 and dest argument refer
to arrays whose component types are different primitive types.
- The
src argument refers to an array with a primitive
component type and the dest argument refers to an array
with a reference component type.
- The
src argument refers to an array with a reference
component type and the dest 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 than
src.length, the length of the source array.
destPos+length is greater than
dest.length, the length of the destination array.
Otherwise, if any actual component of the source array from
position srcPos through
srcPos+length-1 cannot be converted to the component
type of the destination array by assignment conversion, an
ArrayStoreException is thrown. In this case, let
k be the smallest nonnegative integer less than
length such that src[srcPos+k]
cannot be converted to the component type of the destination
array; when the exception is thrown, source array components from
positions srcPos through
srcPos+k-1
will already have been copied to destination array positions
destPos through
destPos+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.
Parameters:
srcPos - starting position in the source array.
Parameters:
dest - the destination array.
Parameters:
destPos - starting position in the destination data.
Parameters:
length - the number of array elements to be copied.
exception:
IndexOutOfBoundsException - if copying would causeaccess of data outside array bounds.
exception:
ArrayStoreException - if an element in the srcarray could not be stored into the dest arraybecause of a type mismatch.
exception:
NullPointerException - if either src ordest is null. |
| console | | public static Console console()(Code) | | Returns the unique
java.io.Console Console object associated
with the current Java virtual machine, if any.
The system console, if any, otherwise null.
since:
1.6 |
| currentTimeMillis | | native public static long currentTimeMillis()(Code) | | 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).
the difference, measured in milliseconds, betweenthe current time and midnight, January 1, 1970 UTC.
See Also: java.util.Date |
| exit | | public static void exit(int status)(Code) | | 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 exit method in class
Runtime. 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 its checkExitmethod doesn't allow exit with the specified status.
See Also: java.lang.Runtime.exit(int) |
| gc | | public static void gc()(Code) | | Runs the garbage collector.
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 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: java.lang.Runtime.gc |
| getProperties | | public static Properties getProperties()(Code) | | Determines the current system properties.
First, if there is a security manager, its
checkPropertiesAccess method is called with no
arguments. This may result in a security exception.
The current set of system properties for use by the
System.getProperty(String) method is returned as a
Properties 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 always includes values
for the following keys:
| Key |
Description of Associated Value |
|---|
java.version |
Java Runtime Environment version |
java.vendor |
Java Runtime Environment vendor | java.vendor.url |
Java vendor URL |
java.home |
Java installation directory |
java.vm.specification.version |
Java Virtual Machine specification 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 |
java.vm.vendor |
Java Virtual Machine implementation vendor |
java.vm.name |
Java Virtual Machine implementation name |
java.specification.version |
Java Runtime Environment specification version |
java.specification.vendor |
Java Runtime Environment specification vendor |
java.specification.name |
Java Runtime Environment specification name |
java.class.version |
Java class format version number |
java.class.path |
Java class path |
java.library.path |
List of paths to search when loading libraries |
java.io.tmpdir |
Default temp file path |
java.compiler |
Name of JIT compiler to use |
java.ext.dirs |
Path of extension directory or directories |
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 |
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 the
System.getProperty(String) operation.
the system properties
exception:
SecurityException - if a security manager exists and itscheckPropertiesAccess method doesn't allow accessto the system properties.
See Also: System.setProperties
See Also: java.lang.SecurityException
See Also: java.lang.SecurityManager.checkPropertiesAccess
See Also: java.util.Properties |
| getSecurityManager | | public static SecurityManager getSecurityManager()(Code) | | Gets the system security interface.
if a security manager has already been established for thecurrent application, then that security manager is returned;otherwise, null is returned.
See Also: System.setSecurityManager |
| getenv | | public static String getenv(String name)(Code) | | Gets the value of the specified environment variable. An
environment variable is a system-dependent external named
value.
If a security manager exists, its
SecurityManager.checkPermission checkPermission method is called with a
RuntimePermission ("getenv."+name)
permission. This may result in a
SecurityException being thrown. If no exception is thrown the value of the
variable name 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 expression
System.getenv("FOO").equals(System.getenv("foo"))
is likely to be true on Microsoft Windows.
Parameters:
name - the name of the environment variable the string value of the variable, or nullif the variable is not defined in the system environment
throws:
NullPointerException - if name is null
throws:
SecurityException - if a security manager exists and itsSecurityManager.checkPermission checkPermissionmethod doesn't allow access to the environment variablename
See Also: System.getenv()
See Also: ProcessBuilder.environment |
| identityHashCode | | native public static int identityHashCode(Object x)(Code) | | 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 the hashCode
since:
JDK1.1 |
| nanoTime | | native public static long nanoTime()(Code) | | 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
System.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 estimatedTime = System.nanoTime() - startTime;
To compare two nanoTime values
long t0 = System.nanoTime(); ... long t1 = System.nanoTime();
one should use
t1 - t0 < 0 , not
t1 < t0 ,
because of the possibility of numerical overflow.
the current value of the running Java Virtual Machine'shigh-resolution time source, in nanoseconds
since:
1.5 |
| runFinalization | | public static void runFinalization()(Code) | | Runs the finalization methods of any objects pending finalization.
Calling this method suggests that the Java Virtual Machine expend
effort toward running the finalize methods of objects
that have been found to be discarded but whose finalize
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 Also: java.lang.Runtime.runFinalization |
| runFinalizersOnExit | | public static void runFinalizersOnExit(boolean value)(Code) | | Enable or disable finalization on exit; doing so specifies that the
finalizers of all objects that have finalizers that have not yet been
automatically invoked are to be run before the Java runtime exits.
By default, finalization on exit is disabled.
If there is a security manager,
its checkExit method is first called
with 0 as its argument to ensure the exit is allowed.
This could result in a SecurityException.
Parameters:
value - indicating enabling or disabling of finalization
throws:
SecurityException - if a security manager exists and its checkExitmethod doesn't allow the exit.
See Also: java.lang.Runtime.exit(int)
See Also: java.lang.Runtime.gc
See Also: java.lang.SecurityManager.checkExit(int)
since:
JDK1.1 |
| setErr | | public static void setErr(PrintStream err)(Code) | | Reassigns the "standard" error output stream.
First, if there is a security manager, its checkPermission
method is called with a RuntimePermission("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 allowreassigning of the standard error output stream.
See Also: SecurityManager.checkPermission
See Also: java.lang.RuntimePermission
since:
JDK1.1 |
| setIn | | public static void setIn(InputStream in)(Code) | | Reassigns the "standard" input stream.
First, if there is a security manager, its checkPermission
method is called with a RuntimePermission("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 allowreassigning of the standard input stream.
See Also: SecurityManager.checkPermission
See Also: java.lang.RuntimePermission
since:
JDK1.1 |
| setOut | | public static void setOut(PrintStream out)(Code) | | Reassigns the "standard" output stream.
First, if there is a security manager, its checkPermission
method is called with a RuntimePermission("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 allowreassigning of the standard output stream.
See Also: SecurityManager.checkPermission
See Also: java.lang.RuntimePermission
since:
JDK1.1 |
| setSecurityManager | | public static void setSecurityManager(SecurityManager s)(Code) | | Sets the System security.
If there is a security manager already installed, this method first
calls the security manager's checkPermission method
with a RuntimePermission("setSecurityManager")
permission to ensure it's ok to replace the existing
security manager.
This may result in throwing a SecurityException.
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.
Parameters:
s - the security manager.
exception:
SecurityException - if the security manager has alreadybeen set and its checkPermission methoddoesn't allow it to be replaced.
See Also: System.getSecurityManager
See Also: SecurityManager.checkPermission
See Also: java.lang.RuntimePermission |
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