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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.
err in out 
arraycopy(Object, int, Object, int, int) currentTimeMillis() exit(int) gc() getenv(String) getProperties() getProperty(String) getProperty(String, String) getSecurityManager() identityHashCode(Object) load(String) loadLibrary(String) libname argument. runFinalization() runFinalizersOnExit(boolean) setErr(PrintStream) setIn(InputStream) setOut(PrintStream) setProperties(Properties) Properties argument. setSecurityManager(SecurityManager) 
in
public static final InputStream in
out
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.
err
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.
setIn
public static void setIn(InputStream in)
setOut
public static void setOut(PrintStream out)
setErr
public static void setErr(PrintStream err)
setSecurityManager
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. getSecurityManager
public static SecurityManager getSecurityManager()
null is returned. currentTimeMillis
public static native 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).
arraycopy
public static native 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 array could not be stored into the dest array because of a type mismatch. identityHashCode
public static native int identityHashCode(Object x)
getProperties
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 |
setProperties
public 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.
getProperty
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.
null if there is no property with that key. getProperty
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.
getenv
public static String getenv(String name)
exit
public static void exit(int status)
This method calls the exit method in class Runtime. This method never returns normally.
gc
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.
runFinalization
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.
runFinalizersOnExit
public static void runFinalizersOnExit(boolean value)
load
public static void load(String filename)
This method calls the load method in class Runtime.
loadLibrary
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. All Packages Class Hierarchy This Package Previous Next Index