System (Java Platform SE 8 ) (original) (raw)

• Method Detail

• setIn

public static void setIn(InputStream in)
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](../../java/lang/SecurityException.html "class in java.lang") - if a security manager exists and itscheckPermission method doesn't allow reassigning of the standard input stream.
Since:
JDK1.1
See Also:
SecurityManager.checkPermission(java.security.Permission), RuntimePermission

• setOut

public static void setOut(PrintStream out)
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](../../java/lang/SecurityException.html "class in java.lang") - if a security manager exists and itscheckPermission method doesn't allow reassigning of the standard output stream.
Since:
JDK1.1
See Also:
SecurityManager.checkPermission(java.security.Permission), RuntimePermission

• setErr

public static void setErr(PrintStream err)
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](../../java/lang/SecurityException.html "class in java.lang") - if a security manager exists and itscheckPermission method doesn't allow reassigning of the standard error output stream.
Since:
JDK1.1
See Also:
SecurityManager.checkPermission(java.security.Permission), RuntimePermission

• console

public static Console console()
Returns the unique Console object associated with the current Java virtual machine, if any.
Returns:
The system console, if any, otherwise null.
Since:
1.6

• inheritedChannel

public static Channel inheritedChannel()
throws IOException
Returns the channel inherited from the entity that created this Java virtual machine.
This method returns the channel obtained by invoking theinheritedChannel method of the system-wide defaultSelectorProvider object.
In addition to the network-oriented channels described ininheritedChannel, this method may return other kinds of channels in the future.
Returns:
The inherited channel, if any, otherwise null.
Throws:
[IOException](../../java/io/IOException.html "class in java.io") - If an I/O error occurs
[SecurityException](../../java/lang/SecurityException.html "class in java.lang") - If a security manager is present and it does not permit access to the channel.
Since:
1.5

• setSecurityManager

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. 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.
Throws:
[SecurityException](../../java/lang/SecurityException.html "class in java.lang") - if the security manager has already been set and its checkPermission method doesn't allow it to be replaced.
See Also:
getSecurityManager(), SecurityManager.checkPermission(java.security.Permission), RuntimePermission

• getSecurityManager

public static SecurityManager getSecurityManager()
Gets the system security interface.
Returns:
if a security manager has already been established for the current application, then that security manager is returned; otherwise, null is returned.
See Also:
setSecurityManager(java.lang.SecurityManager)

• currentTimeMillis

public static long currentTimeMillis()
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).
Returns:
the difference, measured in milliseconds, between the current time and midnight, January 1, 1970 UTC.
See Also:
Date

• nanoTime

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). 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 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.
Returns:
the current value of the running Java Virtual Machine's high-resolution time source, in nanoseconds
Since:
1.5

• arraycopy

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. The number of components copied is equal to the length argument. The components at positions srcPos throughsrcPos+length-1 in the source array are copied into positions destPos throughdestPos+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 throughsrcPos+length-1 were first copied to a temporary array with length components and then the contents of the temporary array were copied into positionsdestPos through destPos+length-1 of the destination array.
If dest is null, then aNullPointerException is thrown.
If src is null, then aNullPointerException is thrown and the destination array is not modified.
Otherwise, if any of the following is true, anArrayStoreException 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, anIndexOutOfBoundsException 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 thansrc.length, the length of the source array.
• destPos+length is greater thandest.length, the length of the destination array.
  Otherwise, if any actual component of the source array from position srcPos throughsrcPos+length-1 cannot be converted to the component type of the destination array by assignment conversion, anArrayStoreException 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 throughsrcPos+k-1 will already have been copied to destination array positionsdestPos throughdestPos+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.
  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.
  Throws:
  [IndexOutOfBoundsException](../../java/lang/IndexOutOfBoundsException.html "class in java.lang") - if copying would cause access of data outside array bounds.
  [ArrayStoreException](../../java/lang/ArrayStoreException.html "class in java.lang") - if an element in the src array could not be stored into the dest array because of a type mismatch.
  [NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if either src ordest is null.

• identityHashCode

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(). The hash code for the null reference is zero.
Parameters:
x - object for which the hashCode is to be calculated
Returns:
the hashCode
Since:
JDK1.1

• getProperties

public static Properties getProperties()
Determines the current system properties.
First, if there is a security manager, itscheckPropertiesAccess method is called with no arguments. This may result in a security exception.
The current set of system properties for use by thegetProperty(String) method is returned as aProperties 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:

• lineSeparator

public static String lineSeparator()
Returns the system-dependent line separator string. It always returns the same value - the initial value of the system property line.separator.
On UNIX systems, it returns "\n"; on Microsoft Windows systems it returns "\r\n".
Returns:
the system-dependent line separator string
Since:
1.7

• setProperties

public static void setProperties(Properties props)
Sets the system properties to the Properties argument.
First, if there is a security manager, itscheckPropertiesAccess 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 isnull, then the current set of system properties is forgotten.
Parameters:
props - the new system properties.
Throws:
[SecurityException](../../java/lang/SecurityException.html "class in java.lang") - if a security manager exists and itscheckPropertiesAccess method doesn't allow access to the system properties.
See Also:
getProperties(), Properties, SecurityException, SecurityManager.checkPropertiesAccess()

• getProperty

public static String getProperty(String key)
Gets the system property indicated by the specified key.
First, if there is a security manager, itscheckPropertyAccess 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.
Parameters:
key - the name of the system property.
Returns:
the string value of the system property, or null if there is no property with that key.
Throws:
[SecurityException](../../java/lang/SecurityException.html "class in java.lang") - if a security manager exists and itscheckPropertyAccess method doesn't allow access to the specified system property.
[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if key isnull.
[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang") - if key is empty.
See Also:
setProperty(java.lang.String, java.lang.String), SecurityException, SecurityManager.checkPropertyAccess(java.lang.String), getProperties()

• getProperty

public static String getProperty(String key,
String def)
Gets the system property indicated by the specified key.
First, if there is a security manager, itscheckPropertyAccess method is called with thekey 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.
def - a default value.
Returns:
the string value of the system property, or the default value if there is no property with that key.
Throws:
[SecurityException](../../java/lang/SecurityException.html "class in java.lang") - if a security manager exists and itscheckPropertyAccess method doesn't allow access to the specified system property.
[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if key isnull.
[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang") - if key is empty.
See Also:
setProperty(java.lang.String, java.lang.String), SecurityManager.checkPropertyAccess(java.lang.String), getProperties()

• setProperty

public static String setProperty(String key,
String value)
Sets the system property indicated by the specified key.
First, if a security manager exists, itsSecurityManager.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.
Parameters:
key - the name of the system property.
value - the value of the system property.
Returns:
the previous value of the system property, or null if it did not have one.
Throws:
[SecurityException](../../java/lang/SecurityException.html "class in java.lang") - if a security manager exists and itscheckPermission method doesn't allow setting of the specified property.
[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if key orvalue is null.
[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang") - if key is empty.
Since:
1.2
See Also:
getProperty(java.lang.String), getProperty(java.lang.String), getProperty(java.lang.String, java.lang.String), PropertyPermission, SecurityManager.checkPermission(java.security.Permission)

• clearProperty

public static String clearProperty(String key)
Removes the system property indicated by the specified key.
First, if a security manager exists, itsSecurityManager.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 removed.
Parameters:
key - the name of the system property to be removed.
Returns:
the previous string value of the system property, or null if there was no property with that key.
Throws:
[SecurityException](../../java/lang/SecurityException.html "class in java.lang") - if a security manager exists and itscheckPropertyAccess method doesn't allow access to the specified system property.
[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if key isnull.
[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang") - if key is empty.
Since:
1.5
See Also:
getProperty(java.lang.String), setProperty(java.lang.String, java.lang.String), Properties, SecurityException, SecurityManager.checkPropertiesAccess()

• getenv

public static String getenv(String name)
Gets the value of the specified environment variable. An environment variable is a system-dependent external named value.
If a security manager exists, itscheckPermission method is called with a[RuntimePermission](../../java/lang/RuntimePermission.html "class in java.lang")("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 expressionSystem.getenv("FOO").equals(System.getenv("foo")) is likely to be true on Microsoft Windows.
Parameters:
name - the name of the environment variable
Returns:
the string value of the variable, or null if the variable is not defined in the system environment
Throws:
[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if name is null
[SecurityException](../../java/lang/SecurityException.html "class in java.lang") - if a security manager exists and itscheckPermission method doesn't allow access to the environment variablename
See Also:
getenv(), ProcessBuilder.environment()

• getenv

public static 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. Attempting to query the presence of a key or value which is not of typeString will throw a ClassCastException.
The returned map and its collection views may not obey the general contract of the Object.equals(java.lang.Object) andObject.hashCode() methods.
The returned map is typically case-sensitive on all platforms.
If a security manager exists, itscheckPermission method is called with a[RuntimePermission](../../java/lang/RuntimePermission.html "class in java.lang")("getenv.*") permission. This may result in a SecurityException being thrown.
When passing information to a Java subprocess,system properties are generally preferred over environment variables.
Returns:
the environment as a map of variable names to values
Throws:
[SecurityException](../../java/lang/SecurityException.html "class in java.lang") - if a security manager exists and itscheckPermission method doesn't allow access to the process environment
Since:
1.5
See Also:
getenv(String), ProcessBuilder.environment()

• exit

public static void exit(int status)
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 classRuntime. 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](../../java/lang/SecurityException.html "class in java.lang") - if a security manager exists and its checkExit method doesn't allow exit with the specified status.
See Also:
Runtime.exit(int)

• gc

public static void gc()
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:
Runtime.gc()

• runFinalization

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. 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:
Runtime.runFinalization()

• runFinalizersOnExit

@Deprecated
public static void runFinalizersOnExit(boolean value)
Deprecated.
Throws UnsupportedOperationException.
The call System.runFinalizersOnExit() is effectively equivalent to the call:

Runtime.runFinalizersOnExit()

Parameters:
value - ignored
Since:
JDK1.1
See Also:
Runtime.runFinalizersOnExit(boolean)

• load

public static void load(String filename)
Loads the native library specified by the filename argument. The filename argument must be an absolute path name. If the filename argument, when stripped of any platform-specific library prefix, path, and file extension, indicates a library whose name is, for example, L, and a native library called L is statically linked with the VM, then the JNI_OnLoad_L function exported by the library is invoked rather than attempting to load a dynamic library. A filename matching the argument does not have to exist in the file system. See the JNI Specification for more details. Otherwise, the filename argument is mapped to a native library image in an implementation-dependent manner.
The call System.load(name) is effectively equivalent to the call:

Runtime.getRuntime().load(name)

Parameters:
filename - the file to load.
Throws:
[SecurityException](../../java/lang/SecurityException.html "class in java.lang") - if a security manager exists and itscheckLink method doesn't allow loading of the specified dynamic library
[UnsatisfiedLinkError](../../java/lang/UnsatisfiedLinkError.html "class in java.lang") - if either the filename is not an absolute path name, the native library is not statically linked with the VM, or the library cannot be mapped to a native library image by the host system.
[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if filename isnull
See Also:
Runtime.load(java.lang.String), SecurityManager.checkLink(java.lang.String)

• loadLibrary

public static void loadLibrary(String libname)
Loads the native library specified by the libname argument. The libname argument must not contain any platform specific prefix, file extension or path. If a native library called libname is statically linked with the VM, then the JNI_OnLoad_libname function exported by the library is invoked. See the JNI Specification for more details. Otherwise, the libname argument is loaded from a system library location and mapped to a native library image in an implementation- dependent manner.
The call System.loadLibrary(name) is effectively equivalent to the call

Runtime.getRuntime().loadLibrary(name)

Parameters:
libname - the name of the library.
Throws:
[SecurityException](../../java/lang/SecurityException.html "class in java.lang") - if a security manager exists and itscheckLink method doesn't allow loading of the specified dynamic library
[UnsatisfiedLinkError](../../java/lang/UnsatisfiedLinkError.html "class in java.lang") - if either the libname argument contains a file path, the native library is not statically linked with the VM, or the library cannot be mapped to a native library image by the host system.
[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if libname isnull
See Also:
Runtime.loadLibrary(java.lang.String), SecurityManager.checkLink(java.lang.String)

• mapLibraryName

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.
Returns:
a platform-dependent native library name.
Throws:
[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if libname isnull
Since:
1.2
See Also:
loadLibrary(java.lang.String), ClassLoader.findLibrary(java.lang.String)