android-35/android/os/SystemProperties.java - platform/prebuilts/fullsdk/sources - Git at Google

 /*
  * Copyright (C) 2006 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package android.os;

 import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.annotation.SystemApi;
 import android.compat.annotation.UnsupportedAppUsage;
 import android.ravenwood.annotation.RavenwoodKeepWholeClass;
 import android.ravenwood.annotation.RavenwoodNativeSubstitutionClass;
 import android.util.Log;
 import android.util.MutableInt;

 import com.android.internal.annotations.GuardedBy;

 import dalvik.annotation.optimization.CriticalNative;
 import dalvik.annotation.optimization.FastNative;

 import libcore.util.HexEncoding;

 import java.nio.charset.StandardCharsets;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.function.Predicate;

 /**
  * Gives access to the system properties store.  The system properties
  * store contains a list of string key-value pairs.
  *
  * <p>Use this class only for the system properties that are local. e.g., within
  * an app, a partition, or a module. For system properties used across the
  * boundaries, formally define them in <code>*.sysprop</code> files and use the
  * auto-generated methods. For more information, see <a href=
  * "https://source.android.com/devices/architecture/sysprops-apis">Implementing
  * System Properties as APIs</a>.</p>
  *
  * {@hide}
  */
 @SystemApi
 @RavenwoodKeepWholeClass
 @RavenwoodNativeSubstitutionClass(
         "com.android.platform.test.ravenwood.nativesubstitution.SystemProperties_host")
 public class SystemProperties {
     private static final String TAG = "SystemProperties";
     private static final boolean TRACK_KEY_ACCESS = false;

     /**
      * Android O removed the property name length limit, but com.amazon.kindle 7.8.1.5
      * uses reflection to read this whenever text is selected (http://b/36095274).
      * @hide
      */
     @UnsupportedAppUsage(trackingBug = 172649311)
     public static final int PROP_NAME_MAX = Integer.MAX_VALUE;

     /** @hide */
     public static final int PROP_VALUE_MAX = 91;

     @UnsupportedAppUsage
     @GuardedBy("sChangeCallbacks")
     private static final ArrayList<Runnable> sChangeCallbacks = new ArrayList<Runnable>();

     @GuardedBy("sRoReads")
     private static final HashMap<String, MutableInt> sRoReads =
             TRACK_KEY_ACCESS ? new HashMap<>() : null;

     private static void onKeyAccess(String key) {
         if (!TRACK_KEY_ACCESS) return;

         if (key != null && key.startsWith("ro.")) {
             synchronized (sRoReads) {
                 MutableInt numReads = sRoReads.getOrDefault(key, null);
                 if (numReads == null) {
                     numReads = new MutableInt(0);
                     sRoReads.put(key, numReads);
                 }
                 numReads.value++;
                 if (numReads.value > 3) {
                     Log.d(TAG, "Repeated read (count=" + numReads.value
                             + ") of a read-only system property '" + key + "'",
                             new Exception());
                 }
             }
         }
     }

     /** @hide */
     public static void init$ravenwood(Map<String, String> values,
             Predicate<String> keyReadablePredicate, Predicate<String> keyWritablePredicate) {
         native_init$ravenwood(values, keyReadablePredicate, keyWritablePredicate,
                 SystemProperties::callChangeCallbacks);
         synchronized (sChangeCallbacks) {
             sChangeCallbacks.clear();
         }
     }

     /** @hide */
     public static void reset$ravenwood() {
         native_reset$ravenwood();
         synchronized (sChangeCallbacks) {
             sChangeCallbacks.clear();
         }
     }

     // These native methods are currently only implemented by Ravenwood, as it's the only
     // mechanism we have to jump to our RavenwoodNativeSubstitutionClass
     private static native void native_init$ravenwood(Map<String, String> values,
             Predicate<String> keyReadablePredicate, Predicate<String> keyWritablePredicate,
             Runnable changeCallback);
     private static native void native_reset$ravenwood();

     // The one-argument version of native_get used to be a regular native function. Nowadays,
     // we use the two-argument form of native_get all the time, but we can't just delete the
     // one-argument overload: apps use it via reflection, as the UnsupportedAppUsage annotation
     // indicates. Let's just live with having a Java function with a very unusual name.
     @UnsupportedAppUsage
     private static String native_get(String key) {
         return native_get(key, "");
     }

     @FastNative
     @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P)
     private static native String native_get(String key, String def);
     @FastNative
     @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P)
     private static native int native_get_int(String key, int def);
     @FastNative
     @UnsupportedAppUsage
     private static native long native_get_long(String key, long def);
     @FastNative
     @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P)
     private static native boolean native_get_boolean(String key, boolean def);

     @FastNative
     private static native long native_find(String name);
     @FastNative
     private static native String native_get(long handle);
     @CriticalNative
     private static native int native_get_int(long handle, int def);
     @CriticalNative
     private static native long native_get_long(long handle, long def);
     @CriticalNative
     private static native boolean native_get_boolean(long handle, boolean def);

     // _NOT_ FastNative: native_set performs IPC and can block
     @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P)
     private static native void native_set(String key, String def);

     @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P)
     private static native void native_add_change_callback();
     private static native void native_report_sysprop_change();

     /**
      * Get the String value for the given {@code key}.
      *
      * @param key the key to lookup
      * @return an empty string if the {@code key} isn't found
      * @hide
      */
     @NonNull
     @SystemApi
     public static String get(@NonNull String key) {
         if (TRACK_KEY_ACCESS) onKeyAccess(key);
         return native_get(key);
     }

     /**
      * Get the String value for the given {@code key}.
      *
      * @param key the key to lookup
      * @param def the default value in case the property is not set or empty
      * @return if the {@code key} isn't found, return {@code def} if it isn't null, or an empty
      * string otherwise
      * @hide
      */
     @NonNull
     @SystemApi
     public static String get(@NonNull String key, @Nullable String def) {
         if (TRACK_KEY_ACCESS) onKeyAccess(key);
         return native_get(key, def);
     }

     /**
      * Get the value for the given {@code key}, and return as an integer.
      *
      * @param key the key to lookup
      * @param def a default value to return
      * @return the key parsed as an integer, or def if the key isn't found or
      *         cannot be parsed
      * @hide
      */
     @SystemApi
     public static int getInt(@NonNull String key, int def) {
         if (TRACK_KEY_ACCESS) onKeyAccess(key);
         return native_get_int(key, def);
     }

     /**
      * Get the value for the given {@code key}, and return as a long.
      *
      * @param key the key to lookup
      * @param def a default value to return
      * @return the key parsed as a long, or def if the key isn't found or
      *         cannot be parsed
      * @hide
      */
     @SystemApi
     public static long getLong(@NonNull String key, long def) {
         if (TRACK_KEY_ACCESS) onKeyAccess(key);
         return native_get_long(key, def);
     }

     /**
      * Get the value for the given {@code key}, returned as a boolean.
      * Values 'n', 'no', '0', 'false' or 'off' are considered false.
      * Values 'y', 'yes', '1', 'true' or 'on' are considered true.
      * (case sensitive).
      * If the key does not exist, or has any other value, then the default
      * result is returned.
      *
      * @param key the key to lookup
      * @param def a default value to return
      * @return the key parsed as a boolean, or def if the key isn't found or is
      *         not able to be parsed as a boolean.
      * @hide
      */
     @SystemApi
     public static boolean getBoolean(@NonNull String key, boolean def) {
         if (TRACK_KEY_ACCESS) onKeyAccess(key);
         return native_get_boolean(key, def);
     }

     /**
      * Set the value for the given {@code key} to {@code val}.
      *
      * @throws IllegalArgumentException for non read-only properties if the {@code val} exceeds
      * 91 characters
      * @throws RuntimeException if the property cannot be set, for example, if it was blocked by
      * SELinux. libc will log the underlying reason.
      * @hide
      */
     @UnsupportedAppUsage
     public static void set(@NonNull String key, @Nullable String val) {
         if (val != null && !key.startsWith("ro.") && val.getBytes(StandardCharsets.UTF_8).length
                 > PROP_VALUE_MAX) {
             throw new IllegalArgumentException("value of system property '" + key
                     + "' is longer than " + PROP_VALUE_MAX + " bytes: " + val);
         }
         if (TRACK_KEY_ACCESS) onKeyAccess(key);
         native_set(key, val);
     }

     /**
      * Add a callback that will be run whenever any system property changes.
      *
      * @param callback The {@link Runnable} that should be executed when a system property
      * changes.
      * @hide
      */
     @UnsupportedAppUsage
     public static void addChangeCallback(@NonNull Runnable callback) {
         synchronized (sChangeCallbacks) {
             if (sChangeCallbacks.size() == 0) {
                 native_add_change_callback();
             }
             sChangeCallbacks.add(callback);
         }
     }

     /**
      * Remove the target callback.
      *
      * @param callback The {@link Runnable} that should be removed.
      * @hide
      */
     @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.R, trackingBug = 170729553)
     public static void removeChangeCallback(@NonNull Runnable callback) {
         synchronized (sChangeCallbacks) {
             if (sChangeCallbacks.contains(callback)) {
                 sChangeCallbacks.remove(callback);
             }
         }
     }

     @SuppressWarnings("unused")  // Called from native code.
     private static void callChangeCallbacks() {
         ArrayList<Runnable> callbacks = null;
         synchronized (sChangeCallbacks) {
             //Log.i("foo", "Calling " + sChangeCallbacks.size() + " change callbacks!");
             if (sChangeCallbacks.size() == 0) {
                 return;
             }
             callbacks = new ArrayList<Runnable>(sChangeCallbacks);
         }
         final long token = Binder.clearCallingIdentity();
         try {
             for (int i = 0; i < callbacks.size(); i++) {
                 try {
                     callbacks.get(i).run();
                 } catch (Throwable t) {
                     // Ignore and try to go on. Don't use wtf here: that
                     // will cause the process to exit on some builds and break tests.
                     Log.e(TAG, "Exception in SystemProperties change callback", t);
                 }
             }
         } finally {
             Binder.restoreCallingIdentity(token);
         }
     }

     /**
      * Notifies listeners that a system property has changed
      * @hide
      */
     @UnsupportedAppUsage
     public static void reportSyspropChanged() {
         native_report_sysprop_change();
     }

     /**
      * Return a {@code SHA-1} digest of the given keys and their values as a
      * hex-encoded string. The ordering of the incoming keys doesn't change the
      * digest result.
      *
      * @hide
      */
     public static @NonNull String digestOf(@NonNull String... keys) {
         Arrays.sort(keys);
         try {
             final MessageDigest digest = MessageDigest.getInstance("SHA-1");
             for (String key : keys) {
                 final String item = key + "=" + get(key) + "\n";
                 digest.update(item.getBytes(StandardCharsets.UTF_8));
             }
             return HexEncoding.encodeToString(digest.digest()).toLowerCase();
         } catch (NoSuchAlgorithmException e) {
             throw new RuntimeException(e);
         }
     }

     @UnsupportedAppUsage
     private SystemProperties() {
     }

     /**
      * Look up a property location by name.
      * @name name of the property
      * @return property handle or {@code null} if property isn't set
      * @hide
      */
     @Nullable public static Handle find(@NonNull String name) {
         long nativeHandle = native_find(name);
         if (nativeHandle == 0) {
             return null;
         }
         return new Handle(nativeHandle);
     }

     /**
      * Handle to a pre-located property. Looking up a property handle in advance allows
      * for optimal repeated lookup of a single property.
      * @hide
      */
     public static final class Handle {

         private final long mNativeHandle;

         /**
          * @return Value of the property
          */
         @NonNull public String get() {
             return native_get(mNativeHandle);
         }
         /**
          * @param def default value
          * @return value or {@code def} on parse error
          */
         public int getInt(int def) {
             return native_get_int(mNativeHandle, def);
         }
         /**
          * @param def default value
          * @return value or {@code def} on parse error
          */
         public long getLong(long def) {
             return native_get_long(mNativeHandle, def);
         }
         /**
          * @param def default value
          * @return value or {@code def} on parse error
          */
         public boolean getBoolean(boolean def) {
             return native_get_boolean(mNativeHandle, def);
         }

         private Handle(long nativeHandle) {
             mNativeHandle = nativeHandle;
         }
     }
 }
	/*
	* Copyright (C) 2006 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	package android.os;

	import android.annotation.NonNull;
	import android.annotation.Nullable;
	import android.annotation.SystemApi;
	import android.compat.annotation.UnsupportedAppUsage;
	import android.ravenwood.annotation.RavenwoodKeepWholeClass;
	import android.ravenwood.annotation.RavenwoodNativeSubstitutionClass;
	import android.util.Log;
	import android.util.MutableInt;

	import com.android.internal.annotations.GuardedBy;

	import dalvik.annotation.optimization.CriticalNative;
	import dalvik.annotation.optimization.FastNative;

	import libcore.util.HexEncoding;

	import java.nio.charset.StandardCharsets;
	import java.security.MessageDigest;
	import java.security.NoSuchAlgorithmException;
	import java.util.ArrayList;
	import java.util.Arrays;
	import java.util.HashMap;
	import java.util.Map;
	import java.util.function.Predicate;

	/**
	* Gives access to the system properties store. The system properties
	* store contains a list of string key-value pairs.
	*
	* <p>Use this class only for the system properties that are local. e.g., within
	* an app, a partition, or a module. For system properties used across the
	* boundaries, formally define them in <code>*.sysprop</code> files and use the
	* auto-generated methods. For more information, see <a href=
	* "https://source.android.com/devices/architecture/sysprops-apis">Implementing
	* System Properties as APIs</a>.</p>
	*
	* {@hide}
	*/
	@SystemApi
	@RavenwoodKeepWholeClass
	@RavenwoodNativeSubstitutionClass(
	"com.android.platform.test.ravenwood.nativesubstitution.SystemProperties_host")
	public class SystemProperties {
	private static final String TAG = "SystemProperties";
	private static final boolean TRACK_KEY_ACCESS = false;

	/**
	* Android O removed the property name length limit, but com.amazon.kindle 7.8.1.5
	* uses reflection to read this whenever text is selected (http://b/36095274).
	* @hide
	*/
	@UnsupportedAppUsage(trackingBug = 172649311)
	public static final int PROP_NAME_MAX = Integer.MAX_VALUE;

	/** @hide */
	public static final int PROP_VALUE_MAX = 91;

	@UnsupportedAppUsage
	@GuardedBy("sChangeCallbacks")
	private static final ArrayList<Runnable> sChangeCallbacks = new ArrayList<Runnable>();

	@GuardedBy("sRoReads")
	private static final HashMap<String, MutableInt> sRoReads =
	TRACK_KEY_ACCESS ? new HashMap<>() : null;

	private static void onKeyAccess(String key) {
	if (!TRACK_KEY_ACCESS) return;

	if (key != null && key.startsWith("ro.")) {
	synchronized (sRoReads) {
	MutableInt numReads = sRoReads.getOrDefault(key, null);
	if (numReads == null) {
	numReads = new MutableInt(0);
	sRoReads.put(key, numReads);
	}
	numReads.value++;
	if (numReads.value > 3) {
	Log.d(TAG, "Repeated read (count=" + numReads.value
	+ ") of a read-only system property '" + key + "'",
	new Exception());
	}
	}
	}
	}

	/** @hide */
	public static void init$ravenwood(Map<String, String> values,
	Predicate<String> keyReadablePredicate, Predicate<String> keyWritablePredicate) {
	native_init$ravenwood(values, keyReadablePredicate, keyWritablePredicate,
	SystemProperties::callChangeCallbacks);
	synchronized (sChangeCallbacks) {
	sChangeCallbacks.clear();
	}
	}

	/** @hide */
	public static void reset$ravenwood() {
	native_reset$ravenwood();
	synchronized (sChangeCallbacks) {
	sChangeCallbacks.clear();
	}
	}

	// These native methods are currently only implemented by Ravenwood, as it's the only
	// mechanism we have to jump to our RavenwoodNativeSubstitutionClass
	private static native void native_init$ravenwood(Map<String, String> values,
	Predicate<String> keyReadablePredicate, Predicate<String> keyWritablePredicate,
	Runnable changeCallback);
	private static native void native_reset$ravenwood();

	// The one-argument version of native_get used to be a regular native function. Nowadays,
	// we use the two-argument form of native_get all the time, but we can't just delete the
	// one-argument overload: apps use it via reflection, as the UnsupportedAppUsage annotation
	// indicates. Let's just live with having a Java function with a very unusual name.
	@UnsupportedAppUsage
	private static String native_get(String key) {
	return native_get(key, "");
	}

	@FastNative
	@UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P)
	private static native String native_get(String key, String def);
	@FastNative
	@UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P)
	private static native int native_get_int(String key, int def);
	@FastNative
	@UnsupportedAppUsage
	private static native long native_get_long(String key, long def);
	@FastNative
	@UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P)
	private static native boolean native_get_boolean(String key, boolean def);

	@FastNative
	private static native long native_find(String name);
	@FastNative
	private static native String native_get(long handle);
	@CriticalNative
	private static native int native_get_int(long handle, int def);
	@CriticalNative
	private static native long native_get_long(long handle, long def);
	@CriticalNative
	private static native boolean native_get_boolean(long handle, boolean def);

	// _NOT_ FastNative: native_set performs IPC and can block
	@UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P)
	private static native void native_set(String key, String def);

	@UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P)
	private static native void native_add_change_callback();
	private static native void native_report_sysprop_change();

	/**
	* Get the String value for the given {@code key}.
	*
	* @param key the key to lookup
	* @return an empty string if the {@code key} isn't found
	* @hide
	*/
	@NonNull
	@SystemApi
	public static String get(@NonNull String key) {
	if (TRACK_KEY_ACCESS) onKeyAccess(key);
	return native_get(key);
	}

	/**
	* Get the String value for the given {@code key}.
	*
	* @param key the key to lookup
	* @param def the default value in case the property is not set or empty
	* @return if the {@code key} isn't found, return {@code def} if it isn't null, or an empty
	* string otherwise
	* @hide
	*/
	@NonNull
	@SystemApi
	public static String get(@NonNull String key, @Nullable String def) {
	if (TRACK_KEY_ACCESS) onKeyAccess(key);
	return native_get(key, def);
	}

	/**
	* Get the value for the given {@code key}, and return as an integer.
	*
	* @param key the key to lookup
	* @param def a default value to return
	* @return the key parsed as an integer, or def if the key isn't found or
	* cannot be parsed
	* @hide
	*/
	@SystemApi
	public static int getInt(@NonNull String key, int def) {
	if (TRACK_KEY_ACCESS) onKeyAccess(key);
	return native_get_int(key, def);
	}

	/**
	* Get the value for the given {@code key}, and return as a long.
	*
	* @param key the key to lookup
	* @param def a default value to return
	* @return the key parsed as a long, or def if the key isn't found or
	* cannot be parsed
	* @hide
	*/
	@SystemApi
	public static long getLong(@NonNull String key, long def) {
	if (TRACK_KEY_ACCESS) onKeyAccess(key);
	return native_get_long(key, def);
	}

	/**
	* Get the value for the given {@code key}, returned as a boolean.
	* Values 'n', 'no', '0', 'false' or 'off' are considered false.
	* Values 'y', 'yes', '1', 'true' or 'on' are considered true.
	* (case sensitive).
	* If the key does not exist, or has any other value, then the default
	* result is returned.
	*
	* @param key the key to lookup
	* @param def a default value to return
	* @return the key parsed as a boolean, or def if the key isn't found or is
	* not able to be parsed as a boolean.
	* @hide
	*/
	@SystemApi
	public static boolean getBoolean(@NonNull String key, boolean def) {
	if (TRACK_KEY_ACCESS) onKeyAccess(key);
	return native_get_boolean(key, def);
	}

	/**
	* Set the value for the given {@code key} to {@code val}.
	*
	* @throws IllegalArgumentException for non read-only properties if the {@code val} exceeds
	* 91 characters
	* @throws RuntimeException if the property cannot be set, for example, if it was blocked by
	* SELinux. libc will log the underlying reason.
	* @hide
	*/
	@UnsupportedAppUsage
	public static void set(@NonNull String key, @Nullable String val) {
	if (val != null && !key.startsWith("ro.") && val.getBytes(StandardCharsets.UTF_8).length
	> PROP_VALUE_MAX) {
	throw new IllegalArgumentException("value of system property '" + key
	+ "' is longer than " + PROP_VALUE_MAX + " bytes: " + val);
	}
	if (TRACK_KEY_ACCESS) onKeyAccess(key);
	native_set(key, val);
	}

	/**
	* Add a callback that will be run whenever any system property changes.
	*
	* @param callback The {@link Runnable} that should be executed when a system property
	* changes.
	* @hide
	*/
	@UnsupportedAppUsage
	public static void addChangeCallback(@NonNull Runnable callback) {
	synchronized (sChangeCallbacks) {
	if (sChangeCallbacks.size() == 0) {
	native_add_change_callback();
	}
	sChangeCallbacks.add(callback);
	}
	}

	/**
	* Remove the target callback.
	*
	* @param callback The {@link Runnable} that should be removed.
	* @hide
	*/
	@UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.R, trackingBug = 170729553)
	public static void removeChangeCallback(@NonNull Runnable callback) {
	synchronized (sChangeCallbacks) {
	if (sChangeCallbacks.contains(callback)) {
	sChangeCallbacks.remove(callback);
	}
	}
	}

	@SuppressWarnings("unused") // Called from native code.
	private static void callChangeCallbacks() {
	ArrayList<Runnable> callbacks = null;
	synchronized (sChangeCallbacks) {
	//Log.i("foo", "Calling " + sChangeCallbacks.size() + " change callbacks!");
	if (sChangeCallbacks.size() == 0) {
	return;
	}
	callbacks = new ArrayList<Runnable>(sChangeCallbacks);
	}
	final long token = Binder.clearCallingIdentity();
	try {
	for (int i = 0; i < callbacks.size(); i++) {
	try {
	callbacks.get(i).run();
	} catch (Throwable t) {
	// Ignore and try to go on. Don't use wtf here: that
	// will cause the process to exit on some builds and break tests.
	Log.e(TAG, "Exception in SystemProperties change callback", t);
	}
	}
	} finally {
	Binder.restoreCallingIdentity(token);
	}
	}

	/**
	* Notifies listeners that a system property has changed
	* @hide
	*/
	@UnsupportedAppUsage
	public static void reportSyspropChanged() {
	native_report_sysprop_change();
	}

	/**
	* Return a {@code SHA-1} digest of the given keys and their values as a
	* hex-encoded string. The ordering of the incoming keys doesn't change the
	* digest result.
	*
	* @hide
	*/
	public static @NonNull String digestOf(@NonNull String... keys) {
	Arrays.sort(keys);
	try {
	final MessageDigest digest = MessageDigest.getInstance("SHA-1");
	for (String key : keys) {
	final String item = key + "=" + get(key) + "\n";
	digest.update(item.getBytes(StandardCharsets.UTF_8));
	}
	return HexEncoding.encodeToString(digest.digest()).toLowerCase();
	} catch (NoSuchAlgorithmException e) {
	throw new RuntimeException(e);
	}
	}

	@UnsupportedAppUsage
	private SystemProperties() {
	}

	/**
	* Look up a property location by name.
	* @name name of the property
	* @return property handle or {@code null} if property isn't set
	* @hide
	*/
	@Nullable public static Handle find(@NonNull String name) {
	long nativeHandle = native_find(name);
	if (nativeHandle == 0) {
	return null;
	}
	return new Handle(nativeHandle);
	}

	/**
	* Handle to a pre-located property. Looking up a property handle in advance allows
	* for optimal repeated lookup of a single property.
	* @hide
	*/
	public static final class Handle {

	private final long mNativeHandle;

	/**
	* @return Value of the property
	*/
	@NonNull public String get() {
	return native_get(mNativeHandle);
	}
	/**
	* @param def default value
	* @return value or {@code def} on parse error
	*/
	public int getInt(int def) {
	return native_get_int(mNativeHandle, def);
	}
	/**
	* @param def default value
	* @return value or {@code def} on parse error
	*/
	public long getLong(long def) {
	return native_get_long(mNativeHandle, def);
	}
	/**
	* @param def default value
	* @return value or {@code def} on parse error
	*/
	public boolean getBoolean(boolean def) {
	return native_get_boolean(mNativeHandle, def);
	}

	private Handle(long nativeHandle) {
	mNativeHandle = nativeHandle;
	}
	}
	}