java.lang.System
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java.lang.Object
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"; a means of
loading files and libraries; and a utility method for quickly
copying a portion of an array.
| Field Summary | |
static PrintStream |
err
The "standard" error output stream. |
static InputStream |
in
The "standard" input stream. |
static PrintStream |
out
The "standard" output stream. |
private static Properties |
props
System properties. |
private static SecurityManager |
security
|
| Constructor Summary | |
private |
System()
Don't let anyone instantiate this class |
| Method Summary | |
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. |
private static void |
checkIO()
|
static long |
currentTimeMillis()
Returns the current time in milliseconds. |
static void |
exit(int status)
Terminates the currently running Java Virtual Machine. |
static void |
gc()
Runs the garbage collector. |
(package private) static Class |
getCallerClass()
|
static String |
getenv(String name)
Deprecated. The preferred way to extract system-dependent information is the system properties of the java.lang.System.getProperty methods and the
corresponding getTypeName methods of
the Boolean, Integer, and
Long primitive types. For example:
|
static Properties |
getProperties()
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 |
getSecurityManager()
Gets the system security interface. |
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(). |
private static void |
initializeSystemClass()
Initialize the system class. |
private static Properties |
initProperties(Properties props)
|
static void |
load(String filename)
Loads a code file with the specified filename from the local file system as a dynamic library. |
static void |
loadLibrary(String libname)
Loads the system library specified by the libname
argument. |
static String |
mapLibraryName(String libname)
Maps a library name into a platform-specific string representing a native library. |
private static InputStream |
nullInputStream()
The following two methods exist because in, out, and err must be initialized to null. |
private static PrintStream |
nullPrintStream()
|
private static void |
registerNatives()
|
static void |
runFinalization()
Runs the finalization methods of any objects pending finalization. |
static void |
runFinalizersOnExit(boolean value)
Deprecated. This method is inherently unsafe. It may result in finalizers being called on live objects while other threads are concurrently manipulating those objects, resulting in erratic behavior or deadlock. |
static void |
setErr(PrintStream err)
Reassigns the "standard" error output stream. |
private static void |
setErr0(PrintStream err)
|
static void |
setIn(InputStream in)
Reassigns the "standard" input stream. |
private static void |
setIn0(InputStream in)
|
static void |
setOut(PrintStream out)
Reassigns the "standard" output stream. |
private static void |
setOut0(PrintStream out)
|
static void |
setProperties(Properties props)
Sets the system properties to the Properties
argument.
|
static String |
setProperty(String key,
String value)
Sets the system property indicated by the specified key. |
static void |
setSecurityManager(SecurityManager s)
Sets the System security. |
private static void |
setSecurityManager0(SecurityManager s)
|
| Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
| Field Detail |
public static final InputStream in
public static final PrintStream out
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 class PrintStream.
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)public static final PrintStream err
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.
private static SecurityManager security
private static Properties props
| Constructor Detail |
private System()
| Method Detail |
private static void registerNatives()
public static void setIn(InputStream in)
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.
in - the new standard input stream.
SecurityException - if a security manager exists and its
checkPermission method doesn't allow
reassigning of the standard input stream.SecurityManager.checkPermission(java.security.Permission),
RuntimePermissionpublic static void setOut(PrintStream out)
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.
out - the new standard output stream
SecurityException - if a security manager exists and its
checkPermission method doesn't allow
reassigning of the standard output stream.SecurityManager.checkPermission(java.security.Permission),
RuntimePermissionpublic static void setErr(PrintStream err)
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.
err - the new standard error output stream.
SecurityException - if a security manager exists and its
checkPermission method doesn't allow
reassigning of the standard error output stream.SecurityManager.checkPermission(java.security.Permission),
RuntimePermissionprivate static void checkIO()
private static void setIn0(InputStream in)
private static void setOut0(PrintStream out)
private static void setErr0(PrintStream err)
public static void setSecurityManager(SecurityManager s)
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.
s - the security manager.
SecurityException - if the security manager has already
been set and its checkPermission method
doesn't allow it to be replaced.getSecurityManager(),
SecurityManager.checkPermission(java.security.Permission),
RuntimePermissionprivate static void setSecurityManager0(SecurityManager s)
public static SecurityManager getSecurityManager()
null is returned.setSecurityManager(java.lang.SecurityManager)public static long currentTimeMillis()
See the description of the class Date for
a discussion of slight discrepancies that may arise between
"computer time" and coordinated universal time (UTC).
Date
public static void arraycopy(Object src,
int srcPos,
Object dest,
int destPos,
int length)
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:
src argument refers to an object that is not an
array.
dest argument refers to an object that is not an
array.
src argument and dest argument refer
to arrays whose component types are different primitive types.
src argument refers to an array with a primitive
component type and the dest argument refers to an array
with a reference component type.
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:
srcPos argument is negative.
destPos argument is negative.
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.)
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.
IndexOutOfBoundsException - if copying would cause
access of data outside array bounds.
ArrayStoreException - if an element in the src
array could not be stored into the dest array
because of a type mismatch.
NullPointerException - if either src or
dest is null.public static int identityHashCode(Object x)
x - object for which the hashCode is to be calculated
private static Properties initProperties(Properties props)
public static Properties getProperties()
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
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
getProperty(String) operation.
SecurityException - if a security manager exists and its
checkPropertiesAccess method doesn't allow access
to the system properties.setProperties(java.util.Properties),
SecurityException,
SecurityManager.checkPropertiesAccess(),
Propertiespublic static void setProperties(Properties props)
Properties
argument.
First, if there is a security manager, its
checkPropertiesAccess 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 is
null, then the current set of system properties is
forgotten.
props - the new system properties.
SecurityException - if a security manager exists and its
checkPropertiesAccess method doesn't allow access
to the system properties.getProperties(),
Properties,
SecurityException,
SecurityManager.checkPropertiesAccess()public static String getProperty(String key)
First, if there is a security manager, its
checkPropertyAccess 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.
key - the name of the system property.
null if there is no property with that key.
SecurityException - if a security manager exists and its
checkPropertyAccess method doesn't allow
access to the specified system property.
NullPointerException - if key is
null.
IllegalArgumentException - if key is empty.setProperty(java.lang.String, java.lang.String),
SecurityException,
SecurityManager.checkPropertyAccess(java.lang.String),
getProperties()
public static String getProperty(String key,
String def)
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.
key - the name of the system property.def - a default value.
SecurityException - if a security manager exists and its
checkPropertyAccess method doesn't allow
access to the specified system property.
NullPointerException - if key is
null.
IllegalArgumentException - if key is empty.setProperty(java.lang.String, java.lang.String),
SecurityManager.checkPropertyAccess(java.lang.String),
getProperties()
public static String setProperty(String key,
String value)
First, if a security manager exists, its
SecurityManager.checkPermission method
is called with a PropertyPermission(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.
key - the name of the system property.value - the value of the system property.
null if it did not have one.
SecurityException - if a security manager exists and its
checkPermission method doesn't allow
setting of the specified property.
NullPointerException - if key is
null.
IllegalArgumentException - if key is empty.getProperty(java.lang.String),
getProperty(java.lang.String),
getProperty(java.lang.String, java.lang.String),
PropertyPermission,
SecurityManager.checkPermission(java.security.Permission)public static String getenv(String name)
java.lang.System.getProperty methods and the
corresponding getTypeName methods of
the Boolean, Integer, and
Long primitive types. For example:
String classPath = System.getProperty("java.class.path",".");
if (Boolean.getBoolean("myapp.exper.mode"))
enableExpertCommands();
name - of the environment variable
null if the variable
is not defined.Boolean.getBoolean(java.lang.String),
Integer.getInteger(java.lang.String),
Integer.getInteger(java.lang.String, int),
Integer.getInteger(java.lang.String, java.lang.Integer),
Long.getLong(java.lang.String),
Long.getLong(java.lang.String, long),
Long.getLong(java.lang.String, java.lang.Long),
getProperties(),
getProperty(java.lang.String),
getProperty(java.lang.String, java.lang.String)public static void exit(int status)
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)
status - exit status.
SecurityException - if a security manager exists and its checkExit
method doesn't allow exit with the specified status.Runtime.exit(int)public static void gc()
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()
Runtime.gc()public static void runFinalization()
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()
Runtime.runFinalization()public static void runFinalizersOnExit(boolean value)
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.
value - indicating enabling or disabling of finalization
SecurityException - if a security manager exists and its checkExit
method doesn't allow the exit.Runtime.exit(int),
Runtime.gc(),
SecurityManager.checkExit(int)public static void load(String filename)
The call System.load(name) is effectively equivalent
to the call:
Runtime.getRuntime().load(name)
filename - the file to load.
SecurityException - if a security manager exists and its
checkLink method doesn't allow
loading of the specified dynamic library
UnsatisfiedLinkError - if the file does not exist.Runtime.load(java.lang.String),
SecurityManager.checkLink(java.lang.String)public static void loadLibrary(String libname)
libname
argument. The manner in which a library name is mapped to the
actual system library is system dependent.
The call System.loadLibrary(name) is effectively
equivalent to the call
Runtime.getRuntime().loadLibrary(name)
libname - the name of the library.
SecurityException - if a security manager exists and its
checkLink method doesn't allow
loading of the specified dynamic library
UnsatisfiedLinkError - if the library does not exist.Runtime.loadLibrary(java.lang.String),
SecurityManager.checkLink(java.lang.String)public static String mapLibraryName(String libname)
libname - the name of the library.
loadLibrary(java.lang.String),
ClassLoader.findLibrary(java.lang.String)
private static InputStream nullInputStream()
throws NullPointerException
NullPointerException
private static PrintStream nullPrintStream()
throws NullPointerException
NullPointerExceptionprivate static void initializeSystemClass()
static Class getCallerClass()
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