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Android Reference



Class 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:
    • Field Detail

      • 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 Detail

      • setIn

        public static void setIn(InputStream newIn)
        Sets the standard input stream to the given user defined input stream.
        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.
        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.
        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.
        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 system time in milliseconds since January 1, 1970 00:00:00 UTC. This method shouldn't be used for measuring timeouts or other elapsed time measurements, as changing the system time can affect the results.
        the local system time in milliseconds.
      • nanoTime

        public static long nanoTime()
        Returns the current timestamp of the most precise timer available on the local system. This timestamp can only be used to measure an elapsed period by comparing it against another timestamp. It cannot be used as a very exact system time expression.
        the current timestamp in nanoseconds.
      • exit

        public static void exit(int code)
        Causes the VM to stop running and the program to exit. If runFinalizersOnExit(boolean) has been previously invoked with a true argument, then all objects will be properly garbage-collected and finalized first.
        code - the return code.
      • 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 var.
        name - the name of the environment variable.
        the value of the specified environment variable or null if no variable exists with the given name.
      • getenv

        public static Map<String,String> getenv()
        Returns an unmodifiable map of all available environment variables.
        the map representing all environment variables.
      • 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.
        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 See File.createTempFile(java.lang.String, java.lang.String) /sdcard
        java.library.path Search path for JNI libraries /system/lib
        java.vendor Human-readable VM vendor The Android Project
        java.vendor.url URL for VM vendor's web site
        java.version (Not useful on Android) 0
        java.specification.version VM libraries version 0.9
        java.specification.vendor VM libraries vendor The Android Project VM libraries name Dalvik Core Library
        java.vm.version VM implementation version 1.2.0
        java.vm.vendor VM implementation vendor The Android Project VM implementation name Dalvik
        java.vm.specification.version VM specification version 0.9
        java.vm.specification.vendor VM specification vendor The Android Project VM specification name Dalvik Virtual Machine Specification
        line.separator The system line separator \n
        os.arch OS architecture armv7l OS (kernel) name Linux
        os.version OS (kernel) version
        path.separator See File.pathSeparator :
        user.dir Base of non-absolute paths /
        user.home (Not useful on Android) Empty (Not useful on Android) Empty

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

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

        public static String getProperty(String prop,
                         String defaultValue)
        Returns the value of a particular system property. The defaultValue will be returned if no such property has been found.
        prop - the name of the system property to look up.
        defaultValue - the return value if the system property with the given name does not exist.
        the value of the specified system property or the defaultValue if the property does not exist.
      • setProperty

        public static String setProperty(String prop,
                         String value)
        Sets the value of a particular system property.
        prop - the name of the system property to be changed.
        value - the value to associate with the given property prop.
        the old value of the property or null if the property didn't exist.
      • clearProperty

        public static String clearProperty(String key)
        Removes a specific system property.
        key - the name of the system property to be removed.
        the property value or null if the property didn't exist.
        NullPointerException - if the argument key is null.
        IllegalArgumentException - if the argument key 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.
      • getSecurityManager

        public static SecurityManager getSecurityManager()
        Returns null. Android does not use SecurityManager. This method is only provided for source compatibility.
      • 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.
        anObject - the object to calculate the hash code.
        the hash code for the given object.
        See Also:
      • 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.
      • 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.
        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.
        libName - the name of the library to load.
        UnsatisfiedLinkError - if the library could not be loaded.
      • logE

        public static void logE(String message)
      • logI

        public static void logI(String message)
      • logW

        public static void logW(String message)
      • 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

        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.
        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.

        sm - a security manager
        SecurityException - always
      • mapLibraryName

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


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