Package java.lang

Class System

java.lang.Object
java.lang.System
public final class System
extends Object
Provides access to system-related information and resources including standard input and output. Enables clients to dynamically load native libraries. All methods of this class are accessed in a static way and the class itself can not be instantiated.
See Also:
Runtime

  • Field Details

    • in

      public static final InputStream in
      Default input stream.

    • out

      public static final PrintStream out
      Default output stream.

    • err

      public static final PrintStream err
      Default error output stream.

  • Method Details

    • setIn

      public static void setIn​(InputStream newIn)
      Sets the standard input stream to the given user defined input stream.
      Parameters:
      newIn - the user defined input stream to set as the standard input stream.

    • setOut

      public static void setOut​(PrintStream newOut)
      Sets the standard output stream to the given user defined output stream.
      Parameters:
      newOut - the user defined output stream to set as the standard output stream.

    • setErr

      public static void setErr​(PrintStream newErr)
      Sets the standard error output stream to the given user defined output stream.
      Parameters:
      newErr - the user defined output stream to set as the standard error output stream.

    • arraycopy

      public static void arraycopy​(Object src, int srcPos, Object dst, int dstPos, int length)
      Copies length elements from the array src, starting at offset srcPos, into the array dst, starting at offset dstPos.

      The source and destination arrays can be the same array, in which case copying is performed as if the source elements are first copied into a temporary array and then into the destination array.

      Parameters:
      src - the source array to copy the content.
      srcPos - the starting index of the content in src.
      dst - the destination array to copy the data into.
      dstPos - the starting index for the copied content in dst.
      length - the number of elements to be copied.

    • currentTimeMillis

      public static long currentTimeMillis()
      Returns the current time in milliseconds since January 1, 1970 00:00:00.0 UTC.

      This method always returns UTC times, regardless of the system's time zone. This is often called "Unix time" or "epoch time". Use a DateFormat instance to format this time for display to a human.

      This method shouldn't be used for measuring timeouts or other elapsed time measurements, as changing the system time can affect the results. Use nanoTime() for that.

    • nanoTime

      public static long nanoTime()
      Returns the current timestamp of the most precise timer available on the local system, in nanoseconds. Equivalent to Linux's CLOCK_MONOTONIC.

      This timestamp should only be used to measure a duration by comparing it against another timestamp on the same device. Values returned by this method do not have a defined correspondence to wall clock times; the zero value is typically whenever the device last booted. Use currentTimeMillis() if you want to know what time it is.

    • exit

      public static void exit​(int code)
      Causes the VM to stop running and the program to exit with the given exit status. If runFinalizersOnExit(boolean) has been previously invoked with a true argument, then all objects will be properly garbage-collected and finalized first.

    • gc

      public static void gc()
      Indicates to the VM that it would be a good time to run the garbage collector. Note that this is a hint only. There is no guarantee that the garbage collector will actually be run.

    • getenv

      public static String getenv​(String name)
      Returns the value of the environment variable with the given name, or null if no such variable exists.

    • getenv

      public static Map<String,​String> getenv()
      Returns an unmodifiable map of all environment variables to their values.

    • inheritedChannel

      public static Channel inheritedChannel() throws IOException
      Returns the inherited channel from the creator of the current virtual machine.
      Returns:
      the inherited Channel or null if none exists.
      Throws:
      IOException - if an I/O error occurred.
      See Also:
      SelectorProvider, SelectorProvider.inheritedChannel()

    • getProperties

      public static Properties getProperties()
      Returns the system properties. Note that this is not a copy, so that changes made to the returned Properties object will be reflected in subsequent calls to getProperty and getProperties.
      Returns:
      the system properties.

    • getProperty

      public static String getProperty​(String propertyName)
      Returns the value of a particular system property or null if no such property exists.

      The following properties are always provided by the Dalvik VM:

      Name Meaning Example
      file.separator File.separator /
      java.class.path System class path .
      java.class.version (Not useful on Android) 50.0
      java.compiler (Not useful on Android) Empty
      java.ext.dirs (Not useful on Android) Empty
      java.home Location of the VM on the file system /system
      java.io.tmpdir See File.createTempFile(java.lang.String, java.lang.String) /sdcard
      java.library.path Search path for JNI libraries /vendor/lib:/system/lib
      java.vendor Human-readable VM vendor The Android Project
      java.vendor.url URL for VM vendor's web site http://www.android.com/
      java.version (Not useful on Android) 0
      java.specification.version VM libraries version 0.9
      java.specification.vendor VM libraries vendor The Android Project
      java.specification.name VM libraries name Dalvik Core Library
      java.vm.version VM implementation version 1.2.0
      java.vm.vendor VM implementation vendor The Android Project
      java.vm.name VM implementation name Dalvik
      java.vm.specification.version VM specification version 0.9
      java.vm.specification.vendor VM specification vendor The Android Project
      java.vm.specification.name VM specification name Dalvik Virtual Machine Specification
      line.separator The system line separator \n
      os.arch OS architecture armv7l
      os.name OS (kernel) name Linux
      os.version OS (kernel) version 2.6.32.9-g103d848
      path.separator See File.pathSeparator :
      user.dir Base of non-absolute paths /
      user.home (Not useful on Android) Empty
      user.name (Not useful on Android) Empty

      It is a mistake to try to override any of these. Doing so will have unpredictable results.

      Parameters:
      propertyName - the name of the system property to look up.
      Returns:
      the value of the specified system property or null if the property doesn't exist.

    • getProperty

      public static String getProperty​(String name, String defaultValue)
      Returns the value of a particular system property. The defaultValue will be returned if no such property has been found.

    • setProperty

      public static String setProperty​(String name, String value)
      Sets the value of a particular system property.
      Returns:
      the old value of the property or null if the property didn't exist.

    • clearProperty

      public static String clearProperty​(String name)
      Removes a specific system property.
      Returns:
      the property value or null if the property didn't exist.
      Throws:
      NullPointerException - if the argument is null.
      IllegalArgumentException - if the argument is empty.

    • console

      public static Console console()
      Returns the Console associated with this VM, or null. Not all VMs will have an associated console. A console is typically only available for programs run from the command line.
      Since:
      1.6

    • getSecurityManager

      public static SecurityManager getSecurityManager()
      Returns null. Android does not use SecurityManager. This method is only provided for source compatibility.
      Returns:
      null

    • identityHashCode

      public static int identityHashCode​(Object anObject)
      Returns an integer hash code for the parameter. The hash code returned is the same one that would be returned by the method java.lang.Object.hashCode(), whether or not the object's class has overridden hashCode(). The hash code for null is 0.
      Parameters:
      anObject - the object to calculate the hash code.
      Returns:
      the hash code for the given object.
      See Also:
      Object.hashCode()

    • lineSeparator

      public static String lineSeparator()
      Returns the system's line separator. On Android, this is "\n". The value comes from the value of the line.separator system property when the VM starts. Later changes to the property will not affect the value returned by this method.
      Since:
      1.7

    • load

      public static void load​(String pathName)
      Loads and links the dynamic library that is identified through the specified path. This method is similar to loadLibrary(String), but it accepts a full path specification whereas loadLibrary just accepts the name of the library to load.
      Parameters:
      pathName - the path of the file to be loaded.

    • loadLibrary

      public static void loadLibrary​(String libName)
      Loads and links the library with the specified name. The mapping of the specified library name to the full path for loading the library is implementation-dependent.
      Parameters:
      libName - the name of the library to load.
      Throws:
      UnsatisfiedLinkError - if the library could not be loaded.

    • logE

      public static void logE​(String message)

    • logE

      public static void logE​(String message, Throwable th)

    • logI

      public static void logI​(String message)

    • logI

      public static void logI​(String message, Throwable th)

    • logW

      public static void logW​(String message)

    • logW

      public static void logW​(String message, Throwable th)

    • runFinalization

      public static void runFinalization()
      Provides a hint to the VM that it would be useful to attempt to perform any outstanding object finalization.

    • runFinalizersOnExit

      @Deprecated public static void runFinalizersOnExit​(boolean flag)
      Deprecated.
      This method is unsafe.
      Ensures that, when the VM is about to exit, all objects are finalized. Note that all finalization which occurs when the system is exiting is performed after all running threads have been terminated.
      Parameters:
      flag - the flag determines if finalization on exit is enabled.

    • setProperties

      public static void setProperties​(Properties p)
      Sets all system properties. This does not take a copy; the passed-in object is used directly. Passing null causes the VM to reinitialize the properties to how they were when the VM was started.

    • setSecurityManager

      public static void setSecurityManager​(SecurityManager sm)
      Throws SecurityException.

      Security managers do not provide a secure environment for executing untrusted code and are unsupported on Android. Untrusted code cannot be safely isolated within a single VM on Android, so this method always throws a SecurityException.

      Parameters:
      sm - a security manager
      Throws:
      SecurityException - always

    • mapLibraryName

      public static String mapLibraryName​(String userLibName)
      Returns the platform specific file name format for the shared library named by the argument.
      Parameters:
      userLibName - the name of the library to look up.
      Returns:
      the platform specific filename for the library.