/*

 * Copyright (c) 1994, 2021, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.lang;

import java.io.BufferedInputStream;

import java.io.BufferedOutputStream;

import java.io.Console;

import java.io.FileDescriptor;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.InputStream;

import java.io.PrintStream;

import java.io.UnsupportedEncodingException;

import java.lang.annotation.Annotation;

import java.lang.invoke.MethodHandle;

import java.lang.invoke.MethodType;

import java.lang.invoke.StringConcatFactory;

import java.lang.module.ModuleDescriptor;

import java.lang.reflect.Constructor;

import java.lang.reflect.Executable;

import java.lang.reflect.Method;

import java.lang.reflect.Modifier;

import java.net.URI;

import java.net.URL;

import java.nio.charset.CharacterCodingException;

import java.nio.channels.Channel;

import java.nio.channels.spi.SelectorProvider;

import java.nio.charset.Charset;

import java.security.AccessControlContext;

import java.security.AccessController;

import java.security.CodeSource;

import java.security.PrivilegedAction;

import java.security.ProtectionDomain;

import java.util.Collections;

import java.util.List;

import java.util.Map;

import java.util.Objects;

import java.util.Properties;

import java.util.PropertyPermission;

import java.util.ResourceBundle;

import java.util.Set;

import java.util.WeakHashMap;

import java.util.function.Supplier;

import java.util.concurrent.ConcurrentHashMap;

import java.util.stream.Stream;

import jdk.internal.misc.Unsafe;

import jdk.internal.util.StaticProperty;

import jdk.internal.module.ModuleBootstrap;

import jdk.internal.module.ServicesCatalog;

import jdk.internal.reflect.CallerSensitive;

import jdk.internal.reflect.Reflection;

import jdk.internal.access.JavaLangAccess;

import jdk.internal.access.SharedSecrets;

import jdk.internal.misc.VM;

import jdk.internal.logger.LoggerFinderLoader;

import jdk.internal.logger.LazyLoggers;

import jdk.internal.logger.LocalizedLoggerWrapper;

import jdk.internal.util.SystemProps;

import jdk.internal.vm.annotation.IntrinsicCandidate;

import jdk.internal.vm.annotation.Stable;

import sun.nio.fs.DefaultFileSystemProvider;

import sun.reflect.annotation.AnnotationType;

import sun.nio.ch.Interruptible;

import sun.security.util.SecurityConstants;

/**

 * The {@code System} class contains several useful class fields

 * and methods. It cannot be instantiated.

 *

 * Among the facilities provided by the {@code 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

 */

public final class System {

    /* Register the natives via the static initializer.

     *

     * The VM will invoke the initPhase1 method to complete the initialization

     * of this class separate from <clinit>.

     */

    private static native void registerNatives();

    static {

        registerNatives();

    }

    /** Don't let anyone instantiate this class */

    private System() {

    }

    /**

     * 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 {@link java.io.InputStreamReader}, {@link Console#charset()}

     * should be used for the charset, or consider using

     * {@link Console#reader()}.

     *

     * @see Console#charset()

     * @see Console#reader()

     */

    public static final InputStream in = null;

    /**

     * 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

     * {@link Console#charset()} if the {@code Console} exists,

     * {@link Charset#defaultCharset()} otherwise.

     * <p>

     * For simple stand-alone Java applications, a typical way to write

     * a line of output data is:

     * <blockquote><pre>

     *     System.out.println(data)

     * </pre></blockquote>

     * <p>

     * See the {@code println} methods in class {@code PrintStream}.

     *

     * @see     java.io.PrintStream#println()

     * @see     java.io.PrintStream#println(boolean)

     * @see     java.io.PrintStream#println(char)

     * @see     java.io.PrintStream#println(char[])

     * @see     java.io.PrintStream#println(double)

     * @see     java.io.PrintStream#println(float)

     * @see     java.io.PrintStream#println(int)

     * @see     java.io.PrintStream#println(long)

     * @see     java.io.PrintStream#println(java.lang.Object)

     * @see     java.io.PrintStream#println(java.lang.String)

     * @see     Console#charset()

     * @see     Charset#defaultCharset()

     */

    public static final PrintStream out = null;

    /**

     * The "standard" error output stream. This stream is already

     * open and ready to accept output data.

     * <p>

     * 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 {@code 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 {@link Console#charset()} if the {@code Console}

     * exists, {@link Charset#defaultCharset()} otherwise.

     *

     * @see     Console#charset()

     * @see     Charset#defaultCharset()

     */

    public static final PrintStream err = null;

    // indicates if a security manager is possible

    private static final int NEVER = 1;

    private static final int MAYBE = 2;

    private static @Stable int allowSecurityManager;

    // current security manager

    @SuppressWarnings("removal")

    private static volatile SecurityManager security;   // read by VM

    // return true if a security manager is allowed

    private static boolean allowSecurityManager() {

        return (allowSecurityManager != NEVER);

    }

    /**

     * Reassigns the "standard" input stream.

     *

     * First, if there is a security manager, its {@code checkPermission}

     * method is called with a {@code RuntimePermission("setIO")} permission

     *  to see if it's ok to reassign the "standard" input stream.

     *

     * @param in the new standard input stream.

     *

     * @throws SecurityException

     *        if a security manager exists and its

     *        {@code checkPermission} method doesn't allow

     *        reassigning of the standard input stream.

     *

     * @see SecurityManager#checkPermission

     * @see java.lang.RuntimePermission

     *

     * @since   1.1

     */

    public static void setIn(InputStream in) {

        checkIO();

        setIn0(in);

    }

    /**

     * Reassigns the "standard" output stream.

     *

     * First, if there is a security manager, its {@code checkPermission}

     * method is called with a {@code RuntimePermission("setIO")} permission

     *  to see if it's ok to reassign the "standard" output stream.

     *

     * @param out the new standard output stream

     *

     * @throws SecurityException

     *        if a security manager exists and its

     *        {@code checkPermission} method doesn't allow

     *        reassigning of the standard output stream.

     *

     * @see SecurityManager#checkPermission

     * @see java.lang.RuntimePermission

     *

     * @since   1.1

     */

    public static void setOut(PrintStream out) {

        checkIO();

        setOut0(out);

    }

    /**

     * Reassigns the "standard" error output stream.

     *

     * First, if there is a security manager, its {@code checkPermission}

     * method is called with a {@code RuntimePermission("setIO")} permission

     *  to see if it's ok to reassign the "standard" error output stream.

     *

     * @param err the new standard error output stream.

     *

     * @throws SecurityException

     *        if a security manager exists and its

     *        {@code checkPermission} method doesn't allow

     *        reassigning of the standard error output stream.

     *

     * @see SecurityManager#checkPermission

     * @see java.lang.RuntimePermission

     *

     * @since   1.1

     */

    public static void setErr(PrintStream err) {

        checkIO();

        setErr0(err);

    }

    private static volatile Console cons;

    /**

     * Returns the unique {@link java.io.Console Console} object associated

     * with the current Java virtual machine, if any.

     *

     * @return  The system console, if any, otherwise {@code null}.

     *

     * @since   1.6

     */

     public static Console console() {

         Console c;

         if ((c = cons) == null) {

             synchronized (System.class) {

                 if ((c = cons) == null) {

                     cons = c = SharedSecrets.getJavaIOAccess().console();

                 }

             }

         }

         return c;

     }

    /**

     * Returns the channel inherited from the entity that created this

     * Java virtual machine.

     *

     * This method returns the channel obtained by invoking the

     * {@link java.nio.channels.spi.SelectorProvider#inheritedChannel

     * inheritedChannel} method of the system-wide default

     * {@link java.nio.channels.spi.SelectorProvider} object.

     *

     * <p> In addition to the network-oriented channels described in

     * {@link java.nio.channels.spi.SelectorProvider#inheritedChannel

     * inheritedChannel}, this method may return other kinds of

     * channels in the future.

     *

     * @return  The inherited channel, if any, otherwise {@code null}.

     *

     * @throws  IOException

     *          If an I/O error occurs

     *

     * @throws  SecurityException

     *          If a security manager is present and it does not

     *          permit access to the channel.

     *

     * @since 1.5

     */

    public static Channel inheritedChannel() throws IOException {

        return SelectorProvider.provider().inheritedChannel();

    }

    private static void checkIO() {

        @SuppressWarnings("removal")

        SecurityManager sm = getSecurityManager();

        if (sm != null) {

            sm.checkPermission(new RuntimePermission("setIO"));

        }

    }

    private static native void setIn0(InputStream in);

    private static native void setOut0(PrintStream out);

    private static native void setErr0(PrintStream err);

    private static class CallersHolder {

        // Remember callers of setSecurityManager() here so that warning

        // is only printed once for each different caller

        final static Map<Class<?>, Boolean> callers

            = Collections.synchronizedMap(new WeakHashMap<>());

    }

    // Remember initial System.err. setSecurityManager() warning goes here

    private static volatile @Stable PrintStream initialErrStream;

    private static URL codeSource(Class<?> clazz) {

        PrivilegedAction<ProtectionDomain> pa = clazz::getProtectionDomain;

        @SuppressWarnings("removal")

        CodeSource cs = AccessController.doPrivileged(pa).getCodeSource();

        return (cs != null) ? cs.getLocation() : null;

    }

    /**

     * Sets the system-wide security manager.

     *

     * If there is a security manager already installed, this method first

     * calls the security manager's {@code checkPermission} method

     * with a {@code RuntimePermission("setSecurityManager")}

     * permission to ensure it's ok to replace the existing

     * security manager.

     * This may result in throwing a {@code SecurityException}.

     *

     * <p> Otherwise, the argument is established as the current

     * security manager. If the argument is {@code null} and no

     * security manager has been established, then no action is taken and

     * the method simply returns.

     *

     * @implNote In the JDK implementation, if the Java virtual machine is

     * started with the system property {@code java.security.manager} set to

     * the special token "{@code disallow}" then the {@code setSecurityManager}

     * method cannot be used to set a security manager.

     *

     * @param  sm the security manager or {@code null}

     * @throws SecurityException

     *         if the security manager has already been set and its {@code

     *         checkPermission} method doesn't allow it to be replaced

     * @throws UnsupportedOperationException

     *         if {@code sm} is non-null and a security manager is not allowed

     *         to be set dynamically

     * @see #getSecurityManager

     * @see SecurityManager#checkPermission

     * @see java.lang.RuntimePermission

     * @deprecated This method is only useful in conjunction with

     *       {@linkplain SecurityManager 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.

     */

    @Deprecated(since="17", forRemoval=true)

    @CallerSensitive

    public static void setSecurityManager(@SuppressWarnings("removal") SecurityManager sm) {

        if (allowSecurityManager()) {

            var callerClass = Reflection.getCallerClass();

            if (CallersHolder.callers.putIfAbsent(callerClass, true) == null) {

                URL url = codeSource(callerClass);

                final String source;

                if (url == null) {

                    source = callerClass.getName();

                } else {

                    source = callerClass.getName() + " (" + url + ")";

                }

                initialErrStream.printf("""

                        WARNING: A terminally deprecated method in java.lang.System has been called

                        WARNING: System::setSecurityManager has been called by %s

                        WARNING: Please consider reporting this to the maintainers of %s

                        WARNING: System::setSecurityManager will be removed in a future release

                        """, source, callerClass.getName());

            }

            implSetSecurityManager(sm);

        } else {

            // security manager not allowed

            if (sm != null) {

                throw new UnsupportedOperationException(

                    "The Security Manager is deprecated and will be removed in a future release");

            }

        }

    }

    private static void implSetSecurityManager(@SuppressWarnings("removal") SecurityManager sm) {

        if (security == null) {

            // ensure image reader is initialized

            Object.class.getResource("java/lang/ANY");

            // ensure the default file system is initialized

            DefaultFileSystemProvider.theFileSystem();

        }

        if (sm != null) {

            try {

                // pre-populates the SecurityManager.packageAccess cache

                // to avoid recursive permission checking issues with custom

                // SecurityManager implementations

                sm.checkPackageAccess("java.lang");

            } catch (Exception e) {

                // no-op

            }

        }

        setSecurityManager0(sm);

    }

    @SuppressWarnings("removal")

    private static synchronized

    void setSecurityManager0(final SecurityManager s) {

        SecurityManager sm = getSecurityManager();

        if (sm != null) {

            // ask the currently installed security manager if we

            // can replace it.

            sm.checkPermission(new RuntimePermission("setSecurityManager"));

        }

        if ((s != null) && (s.getClass().getClassLoader() != null)) {

            // New security manager class is not on bootstrap classpath.

            // Force policy to get initialized before we install the new

            // security manager, in order to prevent infinite loops when

            // trying to initialize the policy (which usually involves

            // accessing some security and/or system properties, which in turn

            // calls the installed security manager's checkPermission method

            // which will loop infinitely if there is a non-system class

            // (in this case: the new security manager class) on the stack).

            AccessController.doPrivileged(new PrivilegedAction<>() {

                public Object run() {

                    s.getClass().getProtectionDomain().implies

                        (SecurityConstants.ALL_PERMISSION);

                    return null;

                }

            });

        }

        security = s;

    }

    /**

     * Gets the system-wide security manager.

     *

     * @return  if a security manager has already been established for the

     *          current application, then that security manager is returned;

     *          otherwise, {@code null} is returned.

     * @see     #setSecurityManager

     * @deprecated This method is only useful in conjunction with

     *       {@linkplain SecurityManager 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.

     */

    @SuppressWarnings("removal")

    @Deprecated(since="17", forRemoval=true)

    public static SecurityManager getSecurityManager() {

        if (allowSecurityManager()) {

            return security;

        } else {

            return null;

        }

    }

    /**

     * 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.

     *

     * <p> See the description of the class {@code Date} for

     * a discussion of slight discrepancies that may arise between

     * "computer time" and coordinated universal time (UTC).

     *

     * @return  the difference, measured in milliseconds, between

     *          the current time and midnight, January 1, 1970 UTC.

     * @see     java.util.Date

     */

    @IntrinsicCandidate

    public static native long currentTimeMillis();

    /**

     * 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 <i>origin</i> 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.

     *

     * <p>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 {@link #currentTimeMillis()}.

     *

     * <p>Differences in successive calls that span greater than

     * approximately 292 years (2<sup>63</sup> nanoseconds) will not

     * correctly compute elapsed time due to numerical overflow.

     *

     * <p>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.

     *

     * <p>For example, to measure how long some code takes to execute:

     * <pre> {@code

     * long startTime = System.nanoTime();

     * // ... the code being measured ...

     * long elapsedNanos = System.nanoTime() - startTime;}</pre>

     *

     * <p>To compare elapsed time against a timeout, use <pre> {@code

     * if (System.nanoTime() - startTime >= timeoutNanos) ...}</pre>

     * instead of <pre> {@code

     * if (System.nanoTime() >= startTime + timeoutNanos) ...}</pre>

     * because of the possibility of numerical overflow.

     *

     * @return the current value of the running Java Virtual Machine's

     *         high-resolution time source, in nanoseconds

     * @since 1.5

     */

    @IntrinsicCandidate

    public static native long nanoTime();

    /**

     * 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 {@code src} to the destination array

     * referenced by {@code dest}. The number of components copied is

     * equal to the {@code length} argument. The components at

     * positions {@code srcPos} through

     * {@code srcPos+length-1} in the source array are copied into

     * positions {@code destPos} through

     * {@code destPos+length-1}, respectively, of the destination

     * array.

     * <p>

     * If the {@code src} and {@code dest} arguments refer to the

     * same array object, then the copying is performed as if the

     * components at positions {@code srcPos} through

     * {@code srcPos+length-1} were first copied to a temporary

     * array with {@code length} components and then the contents of

     * the temporary array were copied into positions

     * {@code destPos} through {@code destPos+length-1} of the

     * destination array.

     * <p>

     * If {@code dest} is {@code null}, then a

     * {@code NullPointerException} is thrown.

     * <p>

     * If {@code src} is {@code null}, then a

     * {@code NullPointerException} is thrown and the destination

     * array is not modified.

     * <p>

     * Otherwise, if any of the following is true, an

     * {@code ArrayStoreException} is thrown and the destination is

     * not modified:

     * <ul>

     * <li>The {@code src} argument refers to an object that is not an

     *     array.

     * <li>The {@code dest} argument refers to an object that is not an

     *     array.

     * <li>The {@code src} argument and {@code dest} argument refer

     *     to arrays whose component types are different primitive types.

     * <li>The {@code src} argument refers to an array with a primitive

     *    component type and the {@code dest} argument refers to an array

     *     with a reference component type.

     * <li>The {@code src} argument refers to an array with a reference

     *    component type and the {@code dest} argument refers to an array

     *     with a primitive component type.

     * </ul>

     * <p>

     * Otherwise, if any of the following is true, an

     * {@code IndexOutOfBoundsException} is

     * thrown and the destination is not modified:

     * <ul>

     * <li>The {@code srcPos} argument is negative.

     * <li>The {@code destPos} argument is negative.

     * <li>The {@code length} argument is negative.

     * <li>{@code srcPos+length} is greater than

     *     {@code src.length}, the length of the source array.

     * <li>{@code destPos+length} is greater than

     *     {@code dest.length}, the length of the destination array.

     * </ul>

     * <p>

     * Otherwise, if any actual component of the source array from

     * position {@code srcPos} through

     * {@code srcPos+length-1} cannot be converted to the component

     * type of the destination array by assignment conversion, an

     * {@code ArrayStoreException} is thrown. In this case, let

     * <b><i>k</i></b> be the smallest nonnegative integer less than

     * length such that {@code src[srcPos+}<i>k</i>{@code ]}

     * cannot be converted to the component type of the destination

     * array; when the exception is thrown, source array components from

     * positions {@code srcPos} through

     * {@code srcPos+}<i>k</i>{@code -1}

     * will already have been copied to destination array positions

     * {@code destPos} through

     * {@code destPos+}<i>k</I>{@code -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.)

     *

     * @param      src      the source array.

     * @param      srcPos   starting position in the source array.

     * @param      dest     the destination array.

     * @param      destPos  starting position in the destination data.

     * @param      length   the number of array elements to be copied.

     * @throws     IndexOutOfBoundsException  if copying would cause

     *             access of data outside array bounds.

     * @throws     ArrayStoreException  if an element in the {@code src}

     *             array could not be stored into the {@code dest} array

     *             because of a type mismatch.

     * @throws     NullPointerException if either {@code src} or

     *             {@code dest} is {@code null}.

     */

    @IntrinsicCandidate

    public static native void arraycopy(Object src,  int  srcPos,

                                        Object dest, int destPos,

                                        int length);

    /**

     * 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.

     *

     * @param x object for which the hashCode is to be calculated

     * @return  the hashCode

     * @since   1.1

     * @see Object#hashCode

     * @see java.util.Objects#hashCode(Object)

     */

    @IntrinsicCandidate

    public static native int identityHashCode(Object x);

    /**

     * System properties.

     *

     * See {@linkplain #getProperties getProperties} for details.

     */

    private static Properties props;

    /**

     * Determines the current system properties.

     *

     * First, if there is a security manager, its

     * {@code checkPropertiesAccess} method is called with no

     * arguments. This may result in a security exception.

     * <p>

     * The current set of system properties for use by the

     * {@link #getProperty(String)} method is returned as a

     * {@code 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.

     * <table class="striped" style="text-align:left">

     * <caption style="display:none">Shows property keys and associated values</caption>

     * <thead>

     * <tr><th scope="col">Key</th>

     *     <th scope="col">Description of Associated Value</th></tr>

     * </thead>

     * <tbody>

     * <tr><th scope="row">{@systemProperty java.version}</th>

     *     <td>Java Runtime Environment version, which may be interpreted

     *     as a {@link Runtime.Version}</td></tr>

     * <tr><th scope="row">{@systemProperty java.version.date}</th>

     *     <td>Java Runtime Environment version date, in ISO-8601 YYYY-MM-DD

     *     format, which may be interpreted as a {@link

     *     java.time.LocalDate}</td></tr>

     * <tr><th scope="row">{@systemProperty java.vendor}</th>

     *     <td>Java Runtime Environment vendor</td></tr>

     * <tr><th scope="row">{@systemProperty java.vendor.url}</th>

     *     <td>Java vendor URL</td></tr>

     * <tr><th scope="row">{@systemProperty java.vendor.version}</th>

     *     <td>Java vendor version <em>(optional)</em> </td></tr>

     * <tr><th scope="row">{@systemProperty java.home}</th>

     *     <td>Java installation directory</td></tr>

     * <tr><th scope="row">{@systemProperty java.vm.specification.version}</th>

     *     <td>Java Virtual Machine specification version, whose value is the

     *     {@linkplain Runtime.Version#feature feature} element of the

     *     {@linkplain Runtime#version() runtime version}</td></tr>

     * <tr><th scope="row">{@systemProperty java.vm.specification.vendor}</th>

     *     <td>Java Virtual Machine specification vendor</td></tr>

     * <tr><th scope="row">{@systemProperty java.vm.specification.name}</th>

     *     <td>Java Virtual Machine specification name</td></tr>

     * <tr><th scope="row">{@systemProperty java.vm.version}</th>

     *     <td>Java Virtual Machine implementation version which may be

     *     interpreted as a {@link Runtime.Version}</td></tr>

     * <tr><th scope="row">{@systemProperty java.vm.vendor}</th>

     *     <td>Java Virtual Machine implementation vendor</td></tr>

     * <tr><th scope="row">{@systemProperty java.vm.name}</th>

     *     <td>Java Virtual Machine implementation name</td></tr>

     * <tr><th scope="row">{@systemProperty java.specification.version}</th>

     *     <td>Java Runtime Environment specification version, whose value is

     *     the {@linkplain Runtime.Version#feature feature} element of the

     *     {@linkplain Runtime#version() runtime version}</td></tr>

     * <tr><th scope="row">{@systemProperty java.specification.vendor}</th>

     *     <td>Java Runtime Environment specification  vendor</td></tr>

     * <tr><th scope="row">{@systemProperty java.specification.name}</th>

     *     <td>Java Runtime Environment specification  name</td></tr>

     * <tr><th scope="row">{@systemProperty java.class.version}</th>

     *     <td>Java class format version number</td></tr>

     * <tr><th scope="row">{@systemProperty java.class.path}</th>

     *     <td>Java class path  (refer to

     *        {@link ClassLoader#getSystemClassLoader()} for details)</td></tr>

     * <tr><th scope="row">{@systemProperty java.library.path}</th>

     *     <td>List of paths to search when loading libraries</td></tr>

     * <tr><th scope="row">{@systemProperty java.io.tmpdir}</th>

     *     <td>Default temp file path</td></tr>

     * <tr><th scope="row">{@systemProperty java.compiler}</th>

     *     <td>Name of JIT compiler to use</td></tr>

     * <tr><th scope="row">{@systemProperty os.name}</th>

     *     <td>Operating system name</td></tr>

     * <tr><th scope="row">{@systemProperty os.arch}</th>

     *     <td>Operating system architecture</td></tr>

     * <tr><th scope="row">{@systemProperty os.version}</th>

     *     <td>Operating system version</td></tr>

     * <tr><th scope="row">{@systemProperty file.separator}</th>

     *     <td>File separator ("/" on UNIX)</td></tr>

     * <tr><th scope="row">{@systemProperty path.separator}</th>

     *     <td>Path separator (":" on UNIX)</td></tr>

     * <tr><th scope="row">{@systemProperty line.separator}</th>

     *     <td>Line separator ("\n" on UNIX)</td></tr>

     * <tr><th scope="row">{@systemProperty user.name}</th>

     *     <td>User's account name</td></tr>

     * <tr><th scope="row">{@systemProperty user.home}</th>

     *     <td>User's home directory</td></tr>

     * <tr><th scope="row">{@systemProperty user.dir}</th>

     *     <td>User's current working directory</td></tr>

     * <tr><th scope="row">{@systemProperty native.encoding}</th>

     *     <td>Character encoding name derived from the host environment and/or

     *     the user's settings. Setting this system property has no effect.</td></tr>

     * </tbody>

     * </table>

     * <p>

     * Multiple paths in a system property value are separated by the path

     * separator character of the platform.

     * <p>

     * Note that even if the security manager does not permit the

     * {@code getProperties} operation, it may choose to permit the

     * {@link #getProperty(String)} operation.

     *

     * @apiNote

     * <strong>Changing a standard system property may have unpredictable results

     * unless otherwise specified.</strong>

     * Property values may be cached during initialization or on first use.

     * Setting a standard property after initialization using {@link #getProperties()},

     * {@link #setProperties(Properties)}, {@link #setProperty(String, String)}, or

     * {@link #clearProperty(String)} may not have the desired effect.

     *

     * @implNote

     * In addition to the standard system properties, the system

     * properties may include the following keys:

     * <table class="striped">

     * <caption style="display:none">Shows property keys and associated values</caption>

     * <thead>

     * <tr><th scope="col">Key</th>

     *     <th scope="col">Description of Associated Value</th></tr>

     * </thead>

     * <tbody>

     * <tr><th scope="row">{@systemProperty jdk.module.path}</th>

     *     <td>The application module path</td></tr>

     * <tr><th scope="row">{@systemProperty jdk.module.upgrade.path}</th>

     *     <td>The upgrade module path</td></tr>

     * <tr><th scope="row">{@systemProperty jdk.module.main}</th>

     *     <td>The module name of the initial/main module</td></tr>

     * <tr><th scope="row">{@systemProperty jdk.module.main.class}</th>

     *     <td>The main class name of the initial module</td></tr>

     * </tbody>

     * </table>

     *

     * @return     the system properties

     * @throws     SecurityException  if a security manager exists and its

     *             {@code checkPropertiesAccess} method doesn't allow access

     *             to the system properties.

     * @see        #setProperties

     * @see        java.lang.SecurityException

     * @see        java.lang.SecurityManager#checkPropertiesAccess()

     * @see        java.util.Properties

     */

    public static Properties getProperties() {

        @SuppressWarnings("removal")

        SecurityManager sm = getSecurityManager();

        if (sm != null) {

            sm.checkPropertiesAccess();

        }

        return props;

    }

    /**

     * Returns the system-dependent line separator string.  It always

     * returns the same value - the initial value of the {@linkplain

     * #getProperty(String) system property} {@code line.separator}.

     *

     * <p>On UNIX systems, it returns {@code "\n"}; on Microsoft

     * Windows systems it returns {@code "\r\n"}.

     *

     * @return the system-dependent line separator string

     * @since 1.7

     */

    public static String lineSeparator() {

        return lineSeparator;

    }

    private static String lineSeparator;

    /**

     * Sets the system properties to the {@code Properties} argument.

     *

     * First, if there is a security manager, its

     * {@code checkPropertiesAccess} method is called with no

     * arguments. This may result in a security exception.

     * <p>

     * The argument becomes the current set of system properties for use

     * by the {@link #getProperty(String)} method. If the argument is

     * {@code null}, then the current set of system properties is

     * forgotten.

     *

     * @apiNote

     * <strong>Changing a standard system property may have unpredictable results

     * unless otherwise specified</strong>.

     * See {@linkplain #getProperties getProperties} for details.

     *

     * @param      props   the new system properties.

     * @throws     SecurityException  if a security manager exists and its

     *             {@code checkPropertiesAccess} method doesn't allow access

     *             to the system properties.

     * @see        #getProperties

     * @see        java.util.Properties

     * @see        java.lang.SecurityException

     * @see        java.lang.SecurityManager#checkPropertiesAccess()

     */

    public static void setProperties(Properties props) {

        @SuppressWarnings("removal")

        SecurityManager sm = getSecurityManager();

        if (sm != null) {

            sm.checkPropertiesAccess();

        }

        if (props == null) {

            Map<String, String> tempProps = SystemProps.initProperties();

            VersionProps.init(tempProps);

            props = createProperties(tempProps);

        }

        System.props = props;

    }

    /**

     * Gets the system property indicated by the specified key.

     *

     * First, if there is a security manager, its

     * {@code checkPropertyAccess} method is called with the key as

     * its argument. This may result in a SecurityException.

     * <p>

     * 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 {@code getProperties} method.

     *

     * @apiNote

     * <strong>Changing a standard system property may have unpredictable results

     * unless otherwise specified</strong>.

     * See {@linkplain #getProperties getProperties} for details.

     *

     * @param      key   the name of the system property.

     * @return     the string value of the system property,

     *             or {@code null} if there is no property with that key.

     *

     * @throws     SecurityException  if a security manager exists and its

     *             {@code checkPropertyAccess} method doesn't allow

     *             access to the specified system property.

     * @throws     NullPointerException if {@code key} is {@code null}.

     * @throws     IllegalArgumentException if {@code key} is empty.

     * @see        #setProperty

     * @see        java.lang.SecurityException

     * @see        java.lang.SecurityManager#checkPropertyAccess(java.lang.String)

     * @see        java.lang.System#getProperties()

     */

    public static String getProperty(String key) {

        checkKey(key);

        @SuppressWarnings("removal")

        SecurityManager sm = getSecurityManager();

        if (sm != null) {

            sm.checkPropertyAccess(key);

        }

        return props.getProperty(key);

    }

    /**

     * Gets the system property indicated by the specified key.

     *

     * First, if there is a security manager, its

     * {@code checkPropertyAccess} method is called with the

     * {@code key} as its argument.

     * <p>

     * 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 {@code getProperties} method.

     *

     * @param      key   the name of the system property.

     * @param      def   a default value.

     * @return     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

     *             {@code checkPropertyAccess} method doesn't allow

     *             access to the specified system property.

     * @throws     NullPointerException if {@code key} is {@code null}.

     * @throws     IllegalArgumentException if {@code key} is empty.

     * @see        #setProperty

     * @see        java.lang.SecurityManager#checkPropertyAccess(java.lang.String)

     * @see        java.lang.System#getProperties()

     */

    public static String getProperty(String key, String def) {

        checkKey(key);

        @SuppressWarnings("removal")

        SecurityManager sm = getSecurityManager();

        if (sm != null) {

            sm.checkPropertyAccess(key);

        }

        return props.getProperty(key, def);

    }

    /**

     * Sets the system property indicated by the specified key.

     *

     * First, if a security manager exists, its

     * {@code SecurityManager.checkPermission} method

     * is called with a {@code 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.

     *

     * @apiNote

     * <strong>Changing a standard system property may have unpredictable results

     * unless otherwise specified</strong>.

     * See {@linkplain #getProperties getProperties} for details.

     *

     * @param      key   the name of the system property.

     * @param      value the value of the system property.

     * @return     the previous value of the system property,

     *             or {@code null} if it did not have one.

     *

     * @throws     SecurityException  if a security manager exists and its

     *             {@code checkPermission} method doesn't allow

     *             setting of the specified property.

     * @throws     NullPointerException if {@code key} or

     *             {@code value} is {@code null}.

     * @throws     IllegalArgumentException if {@code key} is empty.

     * @see        #getProperty

     * @see        java.lang.System#getProperty(java.lang.String)

     * @see        java.lang.System#getProperty(java.lang.String, java.lang.String)

     * @see        java.util.PropertyPermission

     * @see        SecurityManager#checkPermission

     * @since      1.2

     */

    public static String setProperty(String key, String value) {

        checkKey(key);

        @SuppressWarnings("removal")

        SecurityManager sm = getSecurityManager();

        if (sm != null) {

            sm.checkPermission(new PropertyPermission(key,

                SecurityConstants.PROPERTY_WRITE_ACTION));

        }

        return (String) props.setProperty(key, value);

    }

    /**

     * Removes the system property indicated by the specified key.

     *

     * First, if a security manager exists, its

     * {@code SecurityManager.checkPermission} method

     * is called with a {@code PropertyPermission(key, "write")}

     * permission. This may result in a SecurityException being thrown.

     * If no exception is thrown, the specified property is removed.

     *

     * @apiNote

     * <strong>Changing a standard system property may have unpredictable results

     * unless otherwise specified</strong>.

     * See {@linkplain #getProperties getProperties} method for details.

     *

     * @param      key   the name of the system property to be removed.

     * @return     the previous string value of the system property,

     *             or {@code null} if there was no property with that key.

     *

     * @throws     SecurityException  if a security manager exists and its

     *             {@code checkPropertyAccess} method doesn't allow

     *              access to the specified system property.

     * @throws     NullPointerException if {@code key} is {@code null}.

     * @throws     IllegalArgumentException if {@code key} is empty.

     * @see        #getProperty

     * @see        #setProperty

     * @see        java.util.Properties

     * @see        java.lang.SecurityException

     * @see        java.lang.SecurityManager#checkPropertiesAccess()

     * @since 1.5

     */

    public static String clearProperty(String key) {

        checkKey(key);

        @SuppressWarnings("removal")

        SecurityManager sm = getSecurityManager();

        if (sm != null) {

            sm.checkPermission(new PropertyPermission(key, "write"));

        }

        return (String) props.remove(key);

    }

    private static void checkKey(String key) {

        if (key == null) {

            throw new NullPointerException("key can't be null");

        }

        if (key.isEmpty()) {

            throw new IllegalArgumentException("key can't be empty");

        }

    }

    /**

     * Gets the value of the specified environment variable. An

     * environment variable is a system-dependent external named

     * value.

     *

     * <p>If a security manager exists, its

     * {@link SecurityManager#checkPermission checkPermission}

     * method is called with a

     * {@link RuntimePermission RuntimePermission("getenv."+name)}

     * permission.  This may result in a {@link SecurityException}

     * being thrown.  If no exception is thrown the value of the

     * variable {@code name} is returned.

     *

     * <p><a id="EnvironmentVSSystemProperties"><i>System

     * properties</i> and <i>environment variables</i></a> 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 {@code PATH}).

     *

     * <p>On UNIX systems the alphabetic case of {@code name} is

     * typically significant, while on Microsoft Windows systems it is

     * typically not.  For example, the expression

     * {@code System.getenv("FOO").equals(System.getenv("foo"))}

     * is likely to be true on Microsoft Windows.

     *

     * @param  name the name of the environment variable

     * @return the string value of the variable, or {@code null}

     *         if the variable is not defined in the system environment

     * @throws NullPointerException if {@code name} is {@code null}

     * @throws SecurityException

     *         if a security manager exists and its

     *         {@link SecurityManager#checkPermission checkPermission}

     *         method doesn't allow access to the environment variable

     *         {@code name}

     * @see    #getenv()

     * @see    ProcessBuilder#environment()

     */

    public static String getenv(String name) {

        @SuppressWarnings("removal")

        SecurityManager sm = getSecurityManager();

        if (sm != null) {

            sm.checkPermission(new RuntimePermission("getenv."+name));

        }

        return ProcessEnvironment.getenv(name);

    }

    /**

     * 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.

     *

     * <p>If the system does not support environment variables, an

     * empty map is returned.

     *

     * <p>The returned map will never contain null keys or values.

     * Attempting to query the presence of a null key or value will

     * throw a {@link NullPointerException}.  Attempting to query

     * the presence of a key or value which is not of type

     * {@link String} will throw a {@link ClassCastException}.

     *

     * <p>The returned map and its collection views may not obey the

     * general contract of the {@link Object#equals} and

     * {@link Object#hashCode} methods.

     *

     * <p>The returned map is typically case-sensitive on all platforms.

     *

     * <p>If a security manager exists, its

     * {@link SecurityManager#checkPermission checkPermission}

     * method is called with a

     * {@link RuntimePermission RuntimePermission("getenv.*")} permission.

     * This may result in a {@link SecurityException} being thrown.

     *

     * <p>When passing information to a Java subprocess,

     * <a href=#EnvironmentVSSystemProperties>system properties</a>

     * are generally preferred over environment variables.

     *

     * @return the environment as a map of variable names to values

     * @throws SecurityException

     *         if a security manager exists and its

     *         {@link SecurityManager#checkPermission checkPermission}

     *         method doesn't allow access to the process environment

     * @see    #getenv(String)

     * @see    ProcessBuilder#environment()

     * @since  1.5

     */

    public static java.util.Map<String,String> getenv() {

        @SuppressWarnings("removal")

        SecurityManager sm = getSecurityManager();

        if (sm != null) {

            sm.checkPermission(new RuntimePermission("getenv.*"));

        }

        return ProcessEnvironment.getenv();

    }

    /**

     * {@code System.Logger} instances log messages that will be

     * routed to the underlying logging framework the {@link System.LoggerFinder

     * LoggerFinder} uses.

     *

     * {@code System.Logger} instances are typically obtained from

     * the {@link java.lang.System System} class, by calling

     * {@link java.lang.System#getLogger(java.lang.String) System.getLogger(loggerName)}

     * or {@link java.lang.System#getLogger(java.lang.String, java.util.ResourceBundle)

     * System.getLogger(loggerName, bundle)}.

     *

     * @see java.lang.System#getLogger(java.lang.String)

     * @see java.lang.System#getLogger(java.lang.String, java.util.ResourceBundle)

     * @see java.lang.System.LoggerFinder

     *

     * @since 9

     */

    public interface Logger {

        /**

         * System {@linkplain Logger loggers} levels.

         *

         * A level has a {@linkplain #getName() name} and {@linkplain

         * #getSeverity() severity}.

         * Level values are {@link #ALL}, {@link #TRACE}, {@link #DEBUG},

         * {@link #INFO}, {@link #WARNING}, {@link #ERROR}, {@link #OFF},

         * by order of increasing severity.

         * <br>

         * {@link #ALL} and {@link #OFF}

         * are simple markers with severities mapped respectively to

         * {@link java.lang.Integer#MIN_VALUE Integer.MIN_VALUE} and

         * {@link java.lang.Integer#MAX_VALUE Integer.MAX_VALUE}.

         * <p>

         * <b>Severity values and Mapping to {@code java.util.logging.Level}.</b>

         * <p>

         * {@linkplain System.Logger.Level System logger levels} are mapped to

         * {@linkplain java.util.logging.Level  java.util.logging levels}

         * of corresponding severity.

         * <br>The mapping is as follows:

         * <br><br>

         * <table class="striped">

         * <caption>System.Logger Severity Level Mapping</caption>

         * <thead>

         * <tr><th scope="col">System.Logger Levels</th>

         *     <th scope="col">java.util.logging Levels</th>

         * </thead>

         * <tbody>

         * <tr><th scope="row">{@link Logger.Level#ALL ALL}</th>

         *     <td>{@link java.util.logging.Level#ALL ALL}</td>

         * <tr><th scope="row">{@link Logger.Level#TRACE TRACE}</th>

         *     <td>{@link java.util.logging.Level#FINER FINER}</td>

         * <tr><th scope="row">{@link Logger.Level#DEBUG DEBUG}</th>

         *     <td>{@link java.util.logging.Level#FINE FINE}</td>

         * <tr><th scope="row">{@link Logger.Level#INFO INFO}</th>

         *     <td>{@link java.util.logging.Level#INFO INFO}</td>

         * <tr><th scope="row">{@link Logger.Level#WARNING WARNING}</th>

         *     <td>{@link java.util.logging.Level#WARNING WARNING}</td>

         * <tr><th scope="row">{@link Logger.Level#ERROR ERROR}</th>

         *     <td>{@link java.util.logging.Level#SEVERE SEVERE}</td>

         * <tr><th scope="row">{@link Logger.Level#OFF OFF}</th>

         *     <td>{@link java.util.logging.Level#OFF OFF}</td>

         * </tbody>

         * </table>

         *