System (Java SE 23 & JDK 23)
Description: declaration: module: java.base, package: java.lang, class: System
Keywords: java.lang.System class

# Class System

java.lang.Object
java.lang.System

public final class System extends Object
The `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 and environment variables; a means of loading files and libraries; and a utility method for quickly copying a portion of an array.

Since:
  1.0

- ## Nested Class Summary

  Nested Classes
  Modifier and Type
  Class
  Description
  `static interface`
  `System.Logger`
  `System.Logger` instances log messages that will be routed to the underlying logging framework the `LoggerFinder` uses.
  `static class`
  `System.LoggerFinder`
  The `LoggerFinder` service is responsible for creating, managing, and configuring loggers to the underlying framework it uses.

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `static final PrintStream`
  `err`
  The "standard" error output stream.
  `static final InputStream`
  `in`
  The "standard" input stream.
  `static final PrintStream`
  `out`
  The "standard" output stream.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `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.
  `static String`
  `clearProperty(String key)`
  Removes the system property indicated by the specified key.
  `static Console`
  `console()`
  Returns the unique `Console` object associated with the current Java virtual machine, if any.
  `static long`
  `currentTimeMillis()`
  Returns the current time in milliseconds.
  `static void`
  `exit(int status)`
  Initiates the shutdown sequence of the Java Virtual Machine.
  `static void`
  `gc()`
  Runs the garbage collector in the Java Virtual Machine.
  `static Map<String,String>`
  `getenv()`
  Returns an unmodifiable string map view of the current system environment.
  `static String`
  `getenv(String name)`
  Gets the value of the specified environment variable.
  `static System.Logger`
  `getLogger(String name)`
  Returns an instance of `Logger` for the caller's use.
  `static System.Logger`
  `getLogger(String name, ResourceBundle bundle)`
  Returns a localizable instance of `Logger` for the caller's use.
  `static Properties`
  `getProperties()`
  Determines the current system properties.
  `static String`
  `getProperty(String key)`
  Gets the system property indicated by the specified key.
  `static String`
  `getProperty(String key, String def)`
  Gets the system property indicated by the specified key.
  `static SecurityManager`
  `getSecurityManager()`
  Deprecated, for removal: This API element is subject to removal in a future version.
  This method is only useful in conjunction with the Security Manager, which is deprecated and subject to removal in a future release.
  `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().
  `static Channel`
  `inheritedChannel()`
  Returns the channel inherited from the entity that created this Java virtual machine.
  `static String`
  `lineSeparator()`
  Returns the system-dependent line separator string.
  `static void`
  `load(String filename)`
  Loads the native library specified by the filename argument.
  `static void`
  `loadLibrary(String libname)`
  Loads the native library specified by the `libname` argument.
  `static String`
  `mapLibraryName(String libname)`
  Maps a library name into a platform-specific string representing a native library.
  `static long`
  `nanoTime()`
  Returns the current value of the running Java Virtual Machine's high-resolution time source, in nanoseconds.
  `static void`
  `runFinalization()`
  Deprecated, for removal: This API element is subject to removal in a future version.
  Finalization has been deprecated for removal.
  `static void`
  `setErr(PrintStream err)`
  Reassigns the "standard" error output stream.
  `static void`
  `setIn(InputStream in)`
  Reassigns the "standard" input stream.
  `static void`
  `setOut(PrintStream out)`
  Reassigns the "standard" output stream.
  `static void`
  `setProperties(Properties props)`
  Sets the system properties to the `Properties` argument.
  `static String`
  `setProperty(String key, String value)`
  Sets the system property indicated by the specified key.
  `static void`
  `setSecurityManager(SecurityManager sm)`
  Deprecated, for removal: This API element is subject to removal in a future version.
  This method is only useful in conjunction with the Security Manager, which is deprecated and subject to removal in a future release.

  ### Methods declared in class java.lang.Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Field Details

  - ### in

    public static final InputStream in
    The "standard" input stream. This stream is already open and ready to supply input data. Typically this stream corresponds to keyboard input or another input source specified by the host environment or user. In case this stream is wrapped in a `InputStreamReader`, `Console.charset()` should be used for the charset, or consider using `Console.reader()`.
    See Also:
      - `Console.charset()`
      - `Console.reader()`

  - ### out

    public static final PrintStream out
    The "standard" output stream. This stream is already open and ready to accept output data. Typically this stream corresponds to display output or another output destination specified by the host environment or user. The encoding used in the conversion from characters to bytes is equivalent to `Console.charset()` if the `Console` exists, stdout.encoding otherwise.

    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`.

    See Also:
      - `PrintStream.println()`
      - `PrintStream.println(boolean)`
      - `PrintStream.println(char)`
      - `PrintStream.println(char[])`
      - `PrintStream.println(double)`
      - `PrintStream.println(float)`
      - `PrintStream.println(int)`
      - `PrintStream.println(long)`
      - `PrintStream.println(java.lang.Object)`
      - `PrintStream.println(java.lang.String)`
      - `Console.charset()`
      - stdout.encoding

  - ### err

    public static final PrintStream err
    The "standard" error output stream. This stream is already open and ready to accept output data.

    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. The encoding used in the conversion from characters to bytes is equivalent to `Console.charset()` if the `Console` exists, stderr.encoding otherwise.

    See Also:
      - `Console.charset()`
      - stderr.encoding

- ## Method Details

  - ### 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` - if a security manager exists and its `checkPermission` method doesn't allow reassigning of the standard input stream.
    Since:
      1.1
    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` - if a security manager exists and its `checkPermission` method doesn't allow reassigning of the standard output stream.
    Since:
      1.1
    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` - if a security manager exists and its `checkPermission` method doesn't allow reassigning of the standard error output stream.
    Since:
      1.1
    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 the `inheritedChannel` method of the system-wide default `SelectorProvider` object.

    In addition to the network-oriented channels described in `inheritedChannel`, this method may return other kinds of channels in the future.

    Returns:
      The inherited channel, if any, otherwise `null`.
    Throws:
      `IOException` - If an I/O error occurs
      `SecurityException` - If a security manager is present and it does not permit access to the channel.
    Since:
      1.5

  - ### setSecurityManager

    @Deprecated(since="17", forRemoval=true) public static void setSecurityManager(SecurityManager sm)
    Deprecated, for removal: This API element is subject to removal in a future version.
    This method is only useful in conjunction with the Security Manager, which is deprecated and subject to removal in a future release. Consequently, this method is also deprecated and subject to removal. There is no replacement for the Security Manager or this method.
    Sets the system-wide security manager. 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.

    Implementation Note:
      In the JDK implementation, if the Java virtual machine is started with the system property `java.security.manager` not set or set to the special token "`disallow`" then the `setSecurityManager` method cannot be used to set a security manager. See the following section of the `SecurityManager` class specification for more details.
    Parameters:
      `sm` - the security manager or `null`
    Throws:
      `SecurityException` - if the security manager has already been set and its `checkPermission` method doesn't allow it to be replaced
      `UnsupportedOperationException` - if `sm` is non-null and a security manager is not allowed to be set dynamically
    See Also:
      - `getSecurityManager()`
      - `SecurityManager.checkPermission(java.security.Permission)`
      - `RuntimePermission`

  - ### getSecurityManager

    @Deprecated(since="17", forRemoval=true) public static SecurityManager getSecurityManager()
    Deprecated, for removal: This API element is subject to removal in a future version.
    This method is only useful in conjunction with the Security Manager, which is deprecated and subject to removal in a future release. Consequently, this method is also deprecated and subject to removal. There is no replacement for the Security Manager or this method.
    Gets the system-wide security manager.
    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 elapsedNanos = System.nanoTime() - startTime;

    To compare elapsed time against a timeout, use

         if (System.nanoTime() - startTime >= timeoutNanos) ...

    instead of

         if (System.nanoTime() >= startTime + timeoutNanos) ...

    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` through `srcPos+length-1` in the source array are copied into positions `destPos` through `destPos+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` through `srcPos+length-1` were first copied to a temporary array with `length` components and then the contents of the temporary array were copied into positions `destPos` through `destPos+length-1` of the destination array.

    If `dest` is `null`, then a `NullPointerException` is thrown.

    If `src` is `null`, then a `NullPointerException` is thrown and the destination array is not modified.

    Otherwise, if any of the following is true, an `ArrayStoreException` 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, an `IndexOutOfBoundsException` 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 than `src.length`, the length of the source array.
    - `destPos+length` is greater than `dest.length`, the length of the destination array.

    Otherwise, if any actual component of the source array from position `srcPos` through `srcPos+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[srcPos+`k`]` cannot be converted to the component type of the destination array; when the exception is thrown, source array components from positions `srcPos` through `srcPos+`k`-1` will already have been copied to destination array positions `destPos` through `destPos+`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` - if copying would cause access of data outside array bounds.
      `ArrayStoreException` - if an element in the `src` array could not be stored into the `dest` array because of a type mismatch.
      `NullPointerException` - if either `src` or `dest` 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:
      1.1
    See Also:
      - `Object.hashCode()`
      - `Objects.hashCode(Object)`

  - ### getProperties

    public static Properties getProperties()
    Determines the current system properties. First, 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 for use by the `getProperty(String)` method 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 includes a value for each of the following keys unless the description of the associated value indicates that the value is optional.

    Shows property keys and associated values
    Key | Description of Associated Value
    --- | ---
    `java.version` | Java Runtime Environment version, which may be interpreted as a `Runtime.Version`
    `java.version.date` | Java Runtime Environment version date, in ISO-8601 YYYY-MM-DD format, which may be interpreted as a `LocalDate`
    `java.vendor` | Java Runtime Environment vendor
    `java.vendor.url` | Java vendor URL
    `java.vendor.version` | Java vendor version (optional)
    `java.home` | Java installation directory
    `java.vm.specification.version` | Java Virtual Machine specification version, whose value is the feature element of the runtime version
    `java.vm.specification.vendor` | Java Virtual Machine specification vendor
    `java.vm.specification.name` | Java Virtual Machine specification name
    `java.vm.version` | Java Virtual Machine implementation version which may be interpreted as a `Runtime.Version`
    `java.vm.vendor` | Java Virtual Machine implementation vendor
    `java.vm.name` | Java Virtual Machine implementation name
    `java.specification.version` | Java Runtime Environment specification version, whose value is the feature element of the runtime version
    `java.specification.maintenance.version` | Java Runtime Environment specification maintenance version, may be interpreted as a positive integer (optional, see below)
    `java.specification.vendor` | Java Runtime Environment specification vendor
    `java.specification.name` | Java Runtime Environment specification name
    `java.class.version` | Latest Java class file format version recognized by the Java runtime as `"MAJOR.MINOR"` where `MAJOR` and `MINOR` are both formatted as decimal integers
    `java.class.path` | Java class path (refer to `ClassLoader.getSystemClassLoader()` for details)
    `java.library.path` | List of paths to search when loading libraries
    `java.io.tmpdir` | Default temp file 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
    `native.encoding` | Character encoding name derived from the host environment and/or the user's settings. Setting this system property has no effect.
    `stdout.encoding` | Character encoding name for `System.out`. The Java runtime can be started with the system property set to `UTF-8`, starting it with the property set to another value leads to undefined behavior.
    `stderr.encoding` | Character encoding name for `System.err`. The Java runtime can be started with the system property set to `UTF-8`, starting it with the property set to another value leads to undefined behavior.

    The `java.specification.maintenance.version` property is defined if the specification implemented by this runtime at the time of its construction had undergone a maintenance release. When defined, its value identifies that maintenance release. To indicate the first maintenance release this property will have the value `"1"`, to indicate the second maintenance release this property will have the value `"2"`, and so on.

    Multiple paths in a system property value are separated by the path separator character of the platform.

    Note that even if the security manager does not permit the `getProperties` operation, it may choose to permit the `getProperty(String)` operation.

    Additional locale-related system properties defined by the `Default Locale` section in the `Locale` class description may also be obtained with this method.

    API Note:
      Changing a standard system property may have unpredictable results unless otherwise specified. Property values may be cached during initialization or on first use. Setting a standard property after initialization using `getProperties()`, `setProperties(Properties)`, `setProperty(String, String)`, or `clearProperty(String)` may not have the desired effect.
    Implementation Note:
      In addition to the standard system properties, the system properties may include the following keys:

      Shows property keys and associated values
      Key | Description of Associated Value
      --- | ---
      `jdk.module.path` | The application module path
      `jdk.module.upgrade.path` | The upgrade module path
      `jdk.module.main` | The module name of the initial/main module
      `jdk.module.main.class` | The main class name of the initial module
      `file.encoding` | The name of the default charset, defaults to `UTF-8`. The property may be set on the command line to the value `UTF-8` or `COMPAT`. If set on the command line to the value `COMPAT` then the value is replaced with the value of the `native.encoding` property during startup. Setting the property to a value other than `UTF-8` or `COMPAT` leads to unspecified behavior.

    Returns:
      the system properties
    Throws:
      `SecurityException` - if a security manager exists and its `checkPropertiesAccess` method doesn't allow access to the system properties.
    See Also:
      - `setProperties(java.util.Properties)`
      - `SecurityException`
      - `SecurityManager.checkPropertiesAccess()`
      - `Properties`

  - ### 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, 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(String)` method. If the argument is `null`, then the current set of system properties is forgotten.

    API Note:
      Changing a standard system property may have unpredictable results unless otherwise specified. See getProperties for details.
    Parameters:
      `props` - the new system properties.
    Throws:
      `SecurityException` - if a security manager exists and its `checkPropertiesAccess` 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, its `checkPropertyAccess` 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.

    API Note:
      Changing a standard system property may have unpredictable results unless otherwise specified. See getProperties for details.
    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` - if a security manager exists and its `checkPropertyAccess` method doesn't allow access to the specified system property.
      `NullPointerException` - if `key` is `null`.
      `IllegalArgumentException` - 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, 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.

    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` - if a security manager exists and its `checkPropertyAccess` method doesn't allow access to the specified system property.
      `NullPointerException` - if `key` is `null`.
      `IllegalArgumentException` - 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, its `SecurityManager.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.
    API Note:
      Changing a standard system property may have unpredictable results unless otherwise specified. See getProperties for details.
    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` - if a security manager exists and its `checkPermission` method doesn't allow setting of the specified property.
      `NullPointerException` - if `key` or `value` is `null`.
      `IllegalArgumentException` - 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, its `SecurityManager.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.
    API Note:
      Changing a standard system property may have unpredictable results unless otherwise specified. See getProperties method for details.
    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` - if a security manager exists and its `checkPropertyAccess` method doesn't allow access to the specified system property.
      `NullPointerException` - if `key` is `null`.
      `IllegalArgumentException` - 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, its `checkPermission` method is called with a `RuntimePermission("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 expression `System.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` - if `name` is `null`
      `SecurityException` - if a security manager exists and its `checkPermission` method doesn't allow access to the environment variable `name`
    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 type `String` will throw a `ClassCastException`.

    The returned map and its collection views may not obey the general contract of the `Object.equals(java.lang.Object)` and `Object.hashCode()` methods.

    The returned map is typically case-sensitive on all platforms.

    If a security manager exists, its `checkPermission` method is called with a `RuntimePermission("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` - if a security manager exists and its `checkPermission` method doesn't allow access to the process environment
    Since:
      1.5
    See Also:
      - `getenv(String)`
      - `ProcessBuilder.environment()`

  - ### getLogger

    public static System.Logger getLogger(String name)
    Returns an instance of `Logger` for the caller's use.
    API Note:
      This method may defer calling the `LoggerFinder.getLogger` method to create an actual logger supplied by the logging backend, for instance, to allow loggers to be obtained during the system initialization time.
    Implementation Requirements:
      Instances returned by this method route messages to loggers obtained by calling `LoggerFinder.getLogger(name, module)`, where `module` is the caller's module. In cases where `System.getLogger` is called from a context where there is no caller frame on the stack (e.g when called directly from a JNI attached thread), `IllegalCallerException` is thrown. To obtain a logger in such a context, use an auxiliary class that will implicitly be identified as the caller, or use the system `LoggerFinder` to obtain a logger instead. Note that doing the latter may eagerly initialize the underlying logging system.
    Parameters:
      `name` - the name of the logger.
    Returns:
      an instance of `System.Logger` that can be used by the calling class.
    Throws:
      `NullPointerException` - if `name` is `null`.
      `IllegalCallerException` - if there is no Java caller frame on the stack.
    Since:
      9

  - ### getLogger

    public static System.Logger getLogger(String name, ResourceBundle bundle)
    Returns a localizable instance of `Logger` for the caller's use. The returned logger will use the provided resource bundle for message localization.
    API Note:
      This method is intended to be used after the system is fully initialized. This method may trigger the immediate loading and initialization of the `System.LoggerFinder` service, which may cause issues if the Java Runtime is not ready to initialize the concrete service implementation yet. System classes which may be loaded early in the boot sequence and need to log localized messages should create a logger using `getLogger(java.lang.String)` and then use the log methods that take a resource bundle as parameter.
    Implementation Requirements:
      The returned logger will perform message localization as specified by `LoggerFinder.getLocalizedLogger(name, bundle, module)`, where `module` is the caller's module. In cases where `System.getLogger` is called from a context where there is no caller frame on the stack (e.g when called directly from a JNI attached thread), `IllegalCallerException` is thrown. To obtain a logger in such a context, use an auxiliary class that will implicitly be identified as the caller, or use the system `LoggerFinder` to obtain a logger instead. Note that doing the latter may eagerly initialize the underlying logging system.
    Parameters:
      `name` - the name of the logger.
      `bundle` - a resource bundle.
    Returns:
      an instance of `System.Logger` which will use the provided resource bundle for message localization.
    Throws:
      `NullPointerException` - if `name` is `null` or `bundle` is `null`.
      `IllegalCallerException` - if there is no Java caller frame on the stack.
    Since:
      9

  - ### exit

    public static void exit(int status)
    Initiates the shutdown sequence of the Java Virtual Machine. Unless the security manager denies exiting, this method initiates the shutdown sequence (if it is not already initiated) and then blocks indefinitely. This method neither returns nor throws an exception; that is, it does not complete either normally or abruptly.

    The argument serves as a status code. By convention, a nonzero status code indicates abnormal termination.

    The call `System.exit(n)` is effectively equivalent to the call:

            Runtime.getRuntime().exit(n)

    Implementation Note:
      The initiation of the shutdown sequence is logged by `Runtime.exit(int)`.
    Parameters:
      `status` - exit status.
    Throws:
      `SecurityException` - 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 in the Java Virtual Machine.

    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 reuse by the Java Virtual Machine. When control returns from the method call, the Java Virtual Machine has made a best effort to reclaim space from all unused objects. There is no guarantee that this effort will recycle any particular number of unused objects, reclaim any particular amount of space, or complete at any particular time, if at all, before the method returns or ever. There is also no guarantee that this effort will determine the change of reachability in any particular number of objects, or that any particular number of `Reference` objects will be cleared and enqueued.

    The call `System.gc()` is effectively equivalent to the call:

    >      Runtime.getRuntime().gc()

    See Also:
      - `Runtime.gc()`

  - ### runFinalization

    @Deprecated(since="18", forRemoval=true) public static void runFinalization()
    Deprecated, for removal: This API element is subject to removal in a future version.
    Finalization has been deprecated for removal. See `Object.finalize()` for background information and details about migration options.

    When running in a JVM in which finalization has been disabled or removed, no objects will be pending finalization, so this method does nothing.

    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 Java Language Specification:
      12.6 Finalization of Class Instances
    See Also:
      - `Runtime.runFinalization()`

  - ### 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` - if a security manager exists and its `checkLink` method doesn't allow loading of the specified dynamic library
      `UnsatisfiedLinkError` - 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` - if `filename` is `null`
    External Specifications
      - Java Native Interface Specification
    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` - if a security manager exists and its `checkLink` method doesn't allow loading of the specified dynamic library
      `UnsatisfiedLinkError` - 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` - if `libname` is `null`
    External Specifications
      - Java Native Interface Specification
    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` - if `libname` is `null`
    Since:
      1.2
    See Also:
      - `loadLibrary(java.lang.String)`
      - `ClassLoader.findLibrary(java.lang.String)`