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Java Platform 1.2 Beta 4 |
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java.lang.Object | +--java.lang.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"; 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. |
| Method Summary | |
| static void | arraycopy(Object src,
int src_position,
Object dst,
int dst_position,
int length)
Copies an array from the specified source array, beginning at the specified position, to the specified position of the destination array. |
| 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. |
| 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,
String def)
Gets the system property indicated by the specified key. |
| static String | getProperty(String key)
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 hashcode for the given object as would be returned by the default method hashCode(), whether or not the given object's class overrides hashCode(). |
| static void | load(String filename)
Loads the specified filename 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. |
| 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. |
| 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 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. |
| 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.
| Method Detail |
public static void setIn(InputStream in)
The setIn method calls
SecurityManager.checkPermission with the
RuntimePermission("setIO")
permission if a SecurityManager is installed.
public static void setOut(PrintStream out)
The setOut method calls
SecurityManager.checkPermission with the
RuntimePermission("setIO")
permission if a SecurityManager is installed.
public static void setErr(PrintStream err)
The setErr method calls
SecurityManager.checkPermission with the
RuntimePermission("setIO")
permission if a SecurityManager is installed.
public static void setSecurityManager(SecurityManager s)
SecurityException
is thrown. 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.public static SecurityManager getSecurityManager()
null is returned.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 src_position,
Object dst,
int dst_position,
int length)
src to the destination array
referenced by dst. The number of components copied is
equal to the length argument. The components at
positions srcOffset through
srcOffset+length-1 in the source array are copied into
positions dstOffset through
dstOffset+length-1, respectively, of the destination
array.
If the src and dst arguments refer to the
same array object, then the copying is performed as if the
components at positions srcOffset through
srcOffset+length-1 were first copied to a temporary
array with length components and then the contents of
the temporary array were copied into positions
dstOffset through dstOffset+length-1 of the
argument array.
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.
dst argument refers to an object that is not an
array.
src argument and dst argument refer to
arrays whose component types are different primitive types.
src argument refers to an array with a primitive
component type and the dst argument refers to an array
with a reference component type.
src argument refers to an array with a reference
component type and the dst argument refers to an array
with a primitive component type.
Otherwise, if any of the following is true, an
ArrayIndexOutOfBoundsException is
thrown and the destination is not modified:
srcOffset argument is negative.
dstOffset argument is negative.
length argument is negative.
srcOffset+length is greater than
src.length, the length of the source array.
dstOffset+length is greater than
dst.length, the length of the destination array.
Otherwise, if any actual component of the source array from
position srcOffset through
srcOffset+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[srcOffset+k]
cannot be converted to the component type of the destination
array; when the exception is thrown, source array components from
positions srcOffset through
srcOffset+k-1
will already have been copied to destination array positions
dstOffset through
dstOffset+k-1 and no other
positions of the destination array will have been modified.
src:
- the source array.
srcpos
- start position in the source array.
dest
- the destination array.
destpos
- start position in the destination data.
length
- the number of array elements to be copied.src
array could not be stored into the dest array
because of a type mismatch.public static int identityHashCode(Object x)
public static Properties getProperties()
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 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 version number |
java.vendor |
Java vendor-specific string |
java.vendor.url |
Java vendor URL |
java.home |
Java installation directory |
java.class.version |
Java class format version number |
java.class.path |
Java class 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 |
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 method. If the argument is
null, then the current set of system properties is
forgotten.
props
- the new system 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 system exception.
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,
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.SecurityManager.checkPropertyAccess(java.lang.String),
getProperties()
public static String setProperty(String key,
String value)
First, the SecurityManager.checkPermission method
is called with the PropertyPermission(key, "write")
permission. This may result in an 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.getProperty(java.lang.String),
getProperty(java.lang.String, java.lang.String),
PropertyPermissionpublic 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();
the
- 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.
status
- exit 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 unused
objects.
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.
Runtime.runFinalization()public static void runFinalizersOnExit(boolean value)
Runtime.exit(int),
Runtime.gc()public static void load(String filename)
This method calls the load method in class
Runtime.
filename
- the file to load.Runtime.load(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.
libname
- the name of the library.Runtime.loadLibrary(java.lang.String)public static String mapLibraryName(String libname)
libname
- the name of the library.loadLibrary(java.lang.String),
ClassLoader.findLibrary(java.lang.String)
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Java Platform 1.2 Beta 4 |
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| SUMMARY: INNER | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD | |||||||||