Class java.lang.System
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Class java.lang.System
java.lang.Object
|
+----java.lang.System
- public final class System
- extends Object
This Class provides a system-independent interface to system functionality. One of the more useful things provided by this Class
are the standard input and output streams. The standard input streams are
used for reading character data. The standard output streams are used for
printing. For example:
System.out.println("Hello World!");
This Class cannot be instantiated or subclassed because all of the methods
and variables are static.
err - Standard error stream.
- in
- Standard input stream.
- out
- Standard output stream.
arraycopy(Object, int, Object, int, int) - Copies an array from the source array, beginning at the
specified position, to the specified position of the destination array.
- currentTimeMillis()
- Returns the current time in milliseconds GMT since the epoch (00:00:00
UTC, January 1, 1970).
- exit(int)
- Exits the virtual machine with an exit code.
- gc()
- Runs the garbage collector.
- getenv(String)
- Obsolete.
- getProperties()
- Gets the System properties.
- getProperty(String)
- Gets the System property indicated by the specified key.
- getProperty(String, String)
- Gets the System property indicated by the specified key and def.
- getSecurityManager()
- Gets the system security interface.
- load(String)
- Loads a dynamic library, given a complete path name.
- loadLibrary(String)
- Loads a dynamic library with the specified library name.
- runFinalization()
- Runs the finalization methods of any objects pending finalization.
- setProperties(Properties)
- Sets the System properties to the specified properties.
- setSecurityManager(SecurityManager)
- Sets the System security.
in
public static InputStream in
- Standard input stream. This stream is used for reading in character
data.
out
public static PrintStream out
- Standard output stream. This stream is used for printing messages.
err
public static PrintStream err
- Standard error stream. This stream can be used to print error messages.
Many applications read in data from an InputStream and output messages via
the PrintStream out statement. Often applications rely on command line
redirection to specify source and destination files. A problem with redirecting
standard output is the incapability of writing messages to the screen if the
output has been redirected to a file. This problem can be overcome by sending
some output to PrintStream out and other output to PrintStream err. The
difference between PrintStream err and PrintStream out is that PrintStream
err is often used for displaying error messages but may be used for any purpose.
setSecurityManager
public static void setSecurityManager(SecurityManager s)
- Sets the System security. This value can only be set once.
- Parameters:
- s - the security manager
- Throws: SecurityException
- If the SecurityManager has already been set.
getSecurityManager
public static SecurityManager getSecurityManager()
- Gets the system security interface.
currentTimeMillis
public static long currentTimeMillis()
- Returns the current time in milliseconds GMT since the epoch (00:00:00
UTC, January 1, 1970). It is a signed 64 bit integer, and so it will
not overflow until the year 292280995.
- See Also:
- Date
arraycopy
public static void arraycopy(Object src,
int src_position,
Object dst,
int dst_position,
int length)
- Copies an array from the source array, beginning at the
specified position, to the specified position of the destination array.
This method does not allocate memory for the destination array. The
memory must already be allocated.
- Parameters:
- src - the source data
- srcpos - start position in the source data
- dest - the destination
- destpos - start position in the destination data
- length - the number of array elements to be copied
- Throws: ArrayIndexOutOfBoundsException
- If copy would cause access of data outside array bounds.
- Throws: ArrayStoreException
- If an element in the src array could could not be stored into the destination array due to a type mismatch
getProperties
public static Properties getProperties()
- Gets the System properties.
setProperties
public static void setProperties(Properties props)
- Sets the System properties to the specified properties.
- Parameters:
- props - the properties to be set
getProperty
public static String getProperty(String key)
- Gets the System property indicated by the specified key.
- Parameters:
- key - the name of the system property
getProperty
public static String getProperty(String key,
String def)
- Gets the System property indicated by the specified key and def.
- Parameters:
- key - the name of the system property
- def - the default value to use if this property is not set
getenv
public static String getenv(String name)
- Obsolete. Gets an environment variable. An environment variable is a
system dependent external variable that has a string value.
- Parameters:
- name - the name of the environment variable
- Returns:
- the value of the variable, or null if the variable is not defined.
exit
public static void exit(int status)
- Exits the virtual machine with an exit code. This method does
not return, use with caution.
- Parameters:
- status - exit status, 0 if successful, other values indicate various error types.
- See Also:
- exit
gc
public static void gc()
- Runs the garbage collector.
- See Also:
- gc
runFinalization
public static void runFinalization()
- Runs the finalization methods of any objects pending finalization.
- See Also:
- gc
load
public static void load(String filename)
- Loads a dynamic library, given a complete path name.
- Parameters:
- filename - the file to load
- Throws: UnsatisfiedLinkError
- If the file does not exist.
- See Also:
- load
loadLibrary
public static void loadLibrary(String libname)
- Loads a dynamic library with the specified library name.
- Parameters:
- libname - the name of the library
- Throws: UnsatisfiedLinkError
- If the library does not exist.
- See Also:
- loadLibrary
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