content: /*
   * Copyright (C) 2014 The Android Open Source Project
   * Copyright (c) 2013, 2015, 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.InputStream;
  import java.io.IOException;
  import java.io.File;
  import java.lang.reflect.Constructor;
  import java.lang.reflect.InvocationTargetException;
  import java.net.MalformedURLException;
  import java.net.URL;
  import java.security.AccessController;
  import java.security.AccessControlContext;
  import java.security.CodeSource;
  import java.security.Policy;
  import java.security.PrivilegedAction;
  import java.security.PrivilegedActionException;
  import java.security.PrivilegedExceptionAction;
  import java.security.ProtectionDomain;
  import java.security.cert.Certificate;
  import java.util.Collections;
  import java.util.Enumeration;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.Set;
  import java.util.Stack;
  import java.util.Map;
  import java.util.Vector;
  import java.util.Hashtable;
  import java.util.WeakHashMap;
  import java.util.concurrent.ConcurrentHashMap;
  import dalvik.system.PathClassLoader;
  import java.util.List;
  import sun.misc.CompoundEnumeration;
  import sun.misc.Resource;
  import sun.misc.URLClassPath;
  import sun.misc.VM;
  import sun.reflect.CallerSensitive;
  import sun.reflect.Reflection;
  import sun.security.util.SecurityConstants;
  
  /**
   * A class loader is an object that is responsible for loading classes. The
   * class <tt>ClassLoader</tt> is an abstract class.  Given the <a
   * href="#name">binary name</a> of a class, a class loader should attempt to
   * locate or generate data that constitutes a definition for the class.  A
   * typical strategy is to transform the name into a file name and then read a
   * "class file" of that name from a file system.
   *
   * <p> Every {@link Class <tt>Class</tt>} object contains a {@link
   * Class#getClassLoader() reference} to the <tt>ClassLoader</tt> that defined
   * it.
   *
   * <p> <tt>Class</tt> objects for array classes are not created by class
   * loaders, but are created automatically as required by the Java runtime.
   * The class loader for an array class, as returned by {@link
   * Class#getClassLoader()} is the same as the class loader for its element
   * type; if the element type is a primitive type, then the array class has no
   * class loader.
   *
   * <p> Applications implement subclasses of <tt>ClassLoader</tt> in order to
   * extend the manner in which the Java virtual machine dynamically loads
   * classes.
   *
   * <p> Class loaders may typically be used by security managers to indicate
   * security domains.
   *
   * <p> The <tt>ClassLoader</tt> class uses a delegation model to search for
   * classes and resources.  Each instance of <tt>ClassLoader</tt> has an
   * associated parent class loader.  When requested to find a class or
   * resource, a <tt>ClassLoader</tt> instance will delegate the search for the
   * class or resource to its parent class loader before attempting to find the
   * class or resource itself.  The virtual machine's built-in class loader,
   * called the "bootstrap class loader", does not itself have a parent but may
   * serve as the parent of a <tt>ClassLoader</tt> instance.
   *
   * <p> Class loaders that support concurrent loading of classes are known as
   * <em>parallel capable</em> class loaders and are required to register
   * themselves at their class initialization time by invoking the
   * {@link
   * #registerAsParallelCapable <tt>ClassLoader.registerAsParallelCapable</tt>}
   * method. Note that the <tt>ClassLoader</tt> class is registered as parallel
   * capable by default. However, its subclasses still need to register themselves
   * if they are parallel capable. <br>
   * In environments in which the delegation model is not strictly
   * hierarchical, class loaders need to be parallel capable, otherwise class
   * loading can lead to deadlocks because the loader lock is held for the
   * duration of the class loading process (see {@link #loadClass
   * <tt>loadClass</tt>} methods).
   *
   * <p> Normally, the Java virtual machine loads classes from the local file
   * system in a platform-dependent manner.  For example, on UNIX systems, the
   * virtual machine loads classes from the directory defined by the
   * <tt>CLASSPATH</tt> environment variable.
   *
   * <p> However, some classes may not originate from a file; they may originate
   * from other sources, such as the network, or they could be constructed by an
   * application.  The method {@link #defineClass(String, byte[], int, int)
   * <tt>defineClass</tt>} converts an array of bytes into an instance of class
   * <tt>Class</tt>. Instances of this newly defined class can be created using
   * {@link Class#newInstance <tt>Class.newInstance</tt>}.
   *
   * <p> The methods and constructors of objects created by a class loader may
   * reference other classes.  To determine the class(es) referred to, the Java
   * virtual machine invokes the {@link #loadClass <tt>loadClass</tt>} method of
   * the class loader that originally created the class.
   *
   * <p> For example, an application could create a network class loader to
   * download class files from a server.  Sample code might look like:
   *
   * <blockquote><pre>
   *   ClassLoader loader&nbsp;= new NetworkClassLoader(host,&nbsp;port);
   *   Object main&nbsp;= loader.loadClass("Main", true).newInstance();
   *       &nbsp;.&nbsp;.&nbsp;.
   * </pre></blockquote>
   *
   * <p> The network class loader subclass must define the methods {@link
   * #findClass <tt>findClass</tt>} and <tt>loadClassData</tt> to load a class
   * from the network.  Once it has downloaded the bytes that make up the class,
   * it should use the method {@link #defineClass <tt>defineClass</tt>} to
   * create a class instance.  A sample implementation is:
   *
   * <blockquote><pre>
   *     class NetworkClassLoader extends ClassLoader {
   *         String host;
   *         int port;
   *
   *         public Class findClass(String name) {
   *             byte[] b = loadClassData(name);
   *             return defineClass(name, b, 0, b.length);
   *         }
   *
   *         private byte[] loadClassData(String name) {
   *             // load the class data from the connection
   *             &nbsp;.&nbsp;.&nbsp;.
   *         }
   *     }
   * </pre></blockquote>
   *
   * <h3> <a name="name">Binary names</a> </h3>
   *
   * <p> Any class name provided as a {@link String} parameter to methods in
   * <tt>ClassLoader</tt> must be a binary name as defined by
   * <cite>The Java&trade; Language Specification</cite>.
   *
   * <p> Examples of valid class names include:
   * <blockquote><pre>
   *   "java.lang.String"
   *   "javax.swing.JSpinner$DefaultEditor"
   *   "java.security.KeyStore$Builder$FileBuilder$1"
   *   "java.net.URLClassLoader$3$1"
   * </pre></blockquote>
   *
   * @see      #resolveClass(Class)
   * @since 1.0
   */
  public abstract class ClassLoader {
  
      static private class SystemClassLoader {
          public static ClassLoader loader = ClassLoader.createSystemClassLoader();
      }
  
      /**
       * To avoid unloading individual classes, {@link java.lang.reflect.Proxy}
       * only generates one class for each set of interfaces. This maps sets of
       * interfaces to the proxy class that implements all of them. It is declared
       * here so that these generated classes can be unloaded with their class
       * loader.
       *
       * @hide
       */
      public final Map<List<Class<?>>, Class<?>> proxyCache =
              new HashMap<List<Class<?>>, Class<?>>();
  
      // The parent class loader for delegation
      // Note: VM hardcoded the offset of this field, thus all new fields
      // must be added *after* it.
      private final ClassLoader parent;
  
      /**
       * Encapsulates the set of parallel capable loader types.
       */
      private static ClassLoader createSystemClassLoader() {
          String classPath = System.getProperty("java.class.path", ".");
          String librarySearchPath = System.getProperty("java.library.path", "");
  
          // String[] paths = classPath.split(":");
          // URL[] urls = new URL[paths.length];
          // for (int i = 0; i < paths.length; i++) {
          // try {
          // urls[i] = new URL("file://" + paths[i]);
          // }
          // catch (Exception ex) {
          // ex.printStackTrace();
          // }
          // }
          //
          // return new java.net.URLClassLoader(urls, null);
  
          // TODO Make this a java.net.URLClassLoader once we have those?
          return new PathClassLoader(classPath, librarySearchPath, BootClassLoader.getInstance());
      }
  
      // The packages defined in this class loader.  Each package name is mapped
      // to its corresponding Package object.
      // @GuardedBy("itself")
      private final HashMap<String, Package> packages = new HashMap<>();
  
      /**
       * Pointer to the allocator used by the runtime to allocate metadata such
       * as ArtFields and ArtMethods.
       */
      private transient long allocator;
  
      /**
       * Pointer to the class table, only used from within the runtime.
       */
      private transient long classTable;
  
      private static Void checkCreateClassLoader() {
          return null;
      }
  
      private ClassLoader(Void unused, ClassLoader parent) {
          this.parent = parent;
      }
  
      /**
       * Creates a new class loader using the specified parent class loader for
       * delegation.
       *
       * <p> If there is a security manager, its {@link
       * SecurityManager#checkCreateClassLoader()
       * <tt>checkCreateClassLoader</tt>} method is invoked.  This may result in
       * a security exception.  </p>
       *
       * @param  parent
       *         The parent class loader
       *
       * @throws  SecurityException
       *          If a security manager exists and its
       *          <tt>checkCreateClassLoader</tt> method doesn't allow creation
       *          of a new class loader.
       *
       * @since  1.2
       */
      protected ClassLoader(ClassLoader parent) {
          this(checkCreateClassLoader(), parent);
      }
  
      /**
       * Creates a new class loader using the <tt>ClassLoader</tt> returned by
       * the method {@link #getSystemClassLoader()
       * <tt>getSystemClassLoader()</tt>} as the parent class loader.
       *
       * <p> If there is a security manager, its {@link
       * SecurityManager#checkCreateClassLoader()
       * <tt>checkCreateClassLoader</tt>} method is invoked.  This may result in
       * a security exception.  </p>
       *
       * @throws  SecurityException
       *          If a security manager exists and its
       *          <tt>checkCreateClassLoader</tt> method doesn't allow creation
       *          of a new class loader.
       */
      protected ClassLoader() {
          this(checkCreateClassLoader(), getSystemClassLoader());
      }
  
      // -- Class --
  
      /**
       * Loads the class with the specified <a href="#name">binary name</a>.
       * This method searches for classes in the same manner as the {@link
       * #loadClass(String, boolean)} method.  It is invoked by the Java virtual
       * machine to resolve class references.  Invoking this method is equivalent
       * to invoking {@link #loadClass(String, boolean) <tt>loadClass(name,
       * false)</tt>}.
       *
       * @param  name
       *         The <a href="#name">binary name</a> of the class
       *
       * @return  The resulting <tt>Class</tt> object
       *
       * @throws  ClassNotFoundException
       *          If the class was not found
       */
      public Class<?> loadClass(String name) throws ClassNotFoundException {
          return loadClass(name, false);
      }
  
      /**
       * Loads the class with the specified <a href="#name">binary name</a>.  The
       * default implementation of this method searches for classes in the
       * following order:
       *
       * <ol>
       *
       *   <li><p> Invoke {@link #findLoadedClass(String)} to check if the class
       *   has already been loaded.  </p></li>
       *
       *   <li><p> Invoke the {@link #loadClass(String) <tt>loadClass</tt>} method
       *   on the parent class loader.  If the parent is <tt>null</tt> the class
       *   loader built-in to the virtual machine is used, instead.  </p></li>
       *
       *   <li><p> Invoke the {@link #findClass(String)} method to find the
       *   class.  </p></li>
       *
       * </ol>
       *
       * <p> If the class was found using the above steps, and the
       * <tt>resolve</tt> flag is true, this method will then invoke the {@link
       * #resolveClass(Class)} method on the resulting <tt>Class</tt> object.
       *
       * <p> Subclasses of <tt>ClassLoader</tt> are encouraged to override {@link
       * #findClass(String)}, rather than this method.  </p>
       *
       *
       * @param  name
       *         The <a href="#name">binary name</a> of the class
       *
       * @param  resolve
       *         If <tt>true</tt> then resolve the class
       *
       * @return  The resulting <tt>Class</tt> object
       *
       * @throws  ClassNotFoundException
       *          If the class could not be found
       */
      // Android-removed: Remove references to getClassLoadingLock
      //                   Remove perf counters.
      //
      // <p> Unless overridden, this method synchronizes on the result of
      // {@link #getClassLoadingLock <tt>getClassLoadingLock</tt>} method
      // during the entire class loading process.
      protected Class<?> loadClass(String name, boolean resolve)
          throws ClassNotFoundException
      {
              // First, check if the class has already been loaded
              Class<?> c = findLoadedClass(name);
              if (c == null) {
                  try {
                      if (parent != null) {
                          c = parent.loadClass(name, false);
                      } else {
                          c = findBootstrapClassOrNull(name);
                      }
                  } catch (ClassNotFoundException e) {
                      // ClassNotFoundException thrown if class not found
                      // from the non-null parent class loader
                  }
  
                  if (c == null) {
                      // If still not found, then invoke findClass in order
                      // to find the class.
                      c = findClass(name);
                  }
              }
              return c;
      }
  
  
      /**
       * Finds the class with the specified <a href="#name">binary name</a>.
       * This method should be overridden by class loader implementations that
       * follow the delegation model for loading classes, and will be invoked by
       * the {@link #loadClass <tt>loadClass</tt>} method after checking the
       * parent class loader for the requested class.  The default implementation
       * throws a <tt>ClassNotFoundException</tt>.
       *
       * @param  name
       *         The <a href="#name">binary name</a> of the class
       *
       * @return  The resulting <tt>Class</tt> object
       *
       * @throws  ClassNotFoundException
       *          If the class could not be found
       *
       * @since  1.2
       */
      protected Class<?> findClass(String name) throws ClassNotFoundException {
          throw new ClassNotFoundException(name);
      }
  
      /**
       * Converts an array of bytes into an instance of class <tt>Class</tt>.
       * Before the <tt>Class</tt> can be used it must be resolved.  This method
       * is deprecated in favor of the version that takes a <a
       * href="#name">binary name</a> as its first argument, and is more secure.
       *
       * @param  b
       *         The bytes that make up the class data.  The bytes in positions
       *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
       *         of a valid class file as defined by
       *         <cite>The Java&trade; Virtual Machine Specification</cite>.
       *
       * @param  off
       *         The start offset in <tt>b</tt> of the class data
       *
       * @param  len
       *         The length of the class data
       *
       * @return  The <tt>Class</tt> object that was created from the specified
       *          class data
       *
       * @throws  ClassFormatError
       *          If the data did not contain a valid class
       *
       * @throws  IndexOutOfBoundsException
       *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
       *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
       *
       * @throws  SecurityException
       *          If an attempt is made to add this class to a package that
       *          contains classes that were signed by a different set of
       *          certificates than this class, or if an attempt is made
       *          to define a class in a package with a fully-qualified name
       *          that starts with "{@code java.}".
       *
       * @see  #loadClass(String, boolean)
       * @see  #resolveClass(Class)
       *
       * @deprecated  Replaced by {@link #defineClass(String, byte[], int, int)
       * defineClass(String, byte[], int, int)}
       */
      @Deprecated
      protected final Class<?> defineClass(byte[] b, int off, int len)
          throws ClassFormatError
      {
          throw new UnsupportedOperationException("can't load this type of class file");
      }
  
      /**
       * Converts an array of bytes into an instance of class <tt>Class</tt>.
       * Before the <tt>Class</tt> can be used it must be resolved.
       *
       * <p> This method assigns a default {@link ProtectionDomain
       * <tt>ProtectionDomain</tt>} to the newly defined class.  The
       * <tt>ProtectionDomain</tt> is effectively granted the same set of
       * permissions returned when {@link
       * Policy#getPermissions(CodeSource)
       * <tt>Policy.getPolicy().getPermissions(new CodeSource(null, null))</tt>}
       * is invoked.  The default domain is created on the first invocation of
       * {@link #defineClass(String, byte[], int, int) <tt>defineClass</tt>},
       * and re-used on subsequent invocations.
       *
       * <p> To assign a specific <tt>ProtectionDomain</tt> to the class, use
       * the {@link #defineClass(String, byte[], int, int,
       * ProtectionDomain) <tt>defineClass</tt>} method that takes a
       * <tt>ProtectionDomain</tt> as one of its arguments.  </p>
       *
       * @param  name
       *         The expected <a href="#name">binary name</a> of the class, or
       *         <tt>null</tt> if not known
       *
       * @param  b
       *         The bytes that make up the class data.  The bytes in positions
       *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
       *         of a valid class file as defined by
       *         <cite>The Java&trade; Virtual Machine Specification</cite>.
       *
       * @param  off
       *         The start offset in <tt>b</tt> of the class data
       *
       * @param  len
       *         The length of the class data
       *
       * @return  The <tt>Class</tt> object that was created from the specified
       *          class data.
       *
       * @throws  ClassFormatError
       *          If the data did not contain a valid class
       *
       * @throws  IndexOutOfBoundsException
       *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
       *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
       *
       * @throws  SecurityException
       *          If an attempt is made to add this class to a package that
       *          contains classes that were signed by a different set of
       *          certificates than this class (which is unsigned), or if
       *          <tt>name</tt> begins with "<tt>java.</tt>".
       *
       * @see  #loadClass(String, boolean)
       * @see  #resolveClass(Class)
       * @see  CodeSource
       * @see  java.security.SecureClassLoader
       *
       * @since  1.1
       */
      protected final Class<?> defineClass(String name, byte[] b, int off, int len)
          throws ClassFormatError
      {
          throw new UnsupportedOperationException("can't load this type of class file");
      }
  
  
      /**
       * Converts an array of bytes into an instance of class <tt>Class</tt>,
       * with an optional <tt>ProtectionDomain</tt>.  If the domain is
       * <tt>null</tt>, then a default domain will be assigned to the class as
       * specified in the documentation for {@link #defineClass(String, byte[],
       * int, int)}.  Before the class can be used it must be resolved.
       *
       * <p> The first class defined in a package determines the exact set of
       * certificates that all subsequent classes defined in that package must
       * contain.  The set of certificates for a class is obtained from the
       * {@link CodeSource <tt>CodeSource</tt>} within the
       * <tt>ProtectionDomain</tt> of the class.  Any classes added to that
       * package must contain the same set of certificates or a
       * <tt>SecurityException</tt> will be thrown.  Note that if
       * <tt>name</tt> is <tt>null</tt>, this check is not performed.
       * You should always pass in the <a href="#name">binary name</a> of the
       * class you are defining as well as the bytes.  This ensures that the
       * class you are defining is indeed the class you think it is.
       *
       * <p> The specified <tt>name</tt> cannot begin with "<tt>java.</tt>", since
       * all classes in the "<tt>java.*</tt> packages can only be defined by the
       * bootstrap class loader.  If <tt>name</tt> is not <tt>null</tt>, it
       * must be equal to the <a href="#name">binary name</a> of the class
       * specified by the byte array "<tt>b</tt>", otherwise a {@link
       * NoClassDefFoundError <tt>NoClassDefFoundError</tt>} will be thrown. </p>
       *
       * @param  name
       *         The expected <a href="#name">binary name</a> of the class, or
       *         <tt>null</tt> if not known
       *
       * @param  b
       *         The bytes that make up the class data. The bytes in positions
       *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
       *         of a valid class file as defined by
       *         <cite>The Java&trade; Virtual Machine Specification</cite>.
       *
       * @param  off
       *         The start offset in <tt>b</tt> of the class data
       *
       * @param  len
       *         The length of the class data
       *
       * @param  protectionDomain
       *         The ProtectionDomain of the class
       *
       * @return  The <tt>Class</tt> object created from the data,
       *          and optional <tt>ProtectionDomain</tt>.
       *
       * @throws  ClassFormatError
       *          If the data did not contain a valid class
       *
       * @throws  NoClassDefFoundError
       *          If <tt>name</tt> is not equal to the <a href="#name">binary
       *          name</a> of the class specified by <tt>b</tt>
       *
       * @throws  IndexOutOfBoundsException
       *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
       *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
       *
       * @throws  SecurityException
       *          If an attempt is made to add this class to a package that
       *          contains classes that were signed by a different set of
       *          certificates than this class, or if <tt>name</tt> begins with
       *          "<tt>java.</tt>".
       */
      // Android-changed: Remove <tt> from link for NoClassDefFoundError
      protected final Class<?> defineClass(String name, byte[] b, int off, int len,
                                           ProtectionDomain protectionDomain)
          throws ClassFormatError
      {
          throw new UnsupportedOperationException("can't load this type of class file");
      }
  
      /**
       * Converts a {@link java.nio.ByteBuffer <tt>ByteBuffer</tt>}
       * into an instance of class <tt>Class</tt>,
       * with an optional <tt>ProtectionDomain</tt>.  If the domain is
       * <tt>null</tt>, then a default domain will be assigned to the class as
       * specified in the documentation for {@link #defineClass(String, byte[],
       * int, int)}.  Before the class can be used it must be resolved.
       *
       * <p>The rules about the first class defined in a package determining the
       * set of certificates for the package, and the restrictions on class names
       * are identical to those specified in the documentation for {@link
       * #defineClass(String, byte[], int, int, ProtectionDomain)}.
       *
       * <p> An invocation of this method of the form
       * <i>cl</i><tt>.defineClass(</tt><i>name</i><tt>,</tt>
       * <i>bBuffer</i><tt>,</tt> <i>pd</i><tt>)</tt> yields exactly the same
       * result as the statements
       *
       *<p> <tt>
       * ...<br>
       * byte[] temp = new byte[bBuffer.{@link
       * java.nio.ByteBuffer#remaining remaining}()];<br>
       *     bBuffer.{@link java.nio.ByteBuffer#get(byte[])
       * get}(temp);<br>
       *     return {@link #defineClass(String, byte[], int, int, ProtectionDomain)
       * cl.defineClass}(name, temp, 0,
       * temp.length, pd);<br>
       * </tt></p>
       *
       * @param  name
       *         The expected <a href="#name">binary name</a>. of the class, or
       *         <tt>null</tt> if not known
       *
       * @param  b
       *         The bytes that make up the class data. The bytes from positions
       *         <tt>b.position()</tt> through <tt>b.position() + b.limit() -1
       *         </tt> should have the format of a valid class file as defined by
       *         <cite>The Java&trade; Virtual Machine Specification</cite>.
       *
       * @param  protectionDomain
       *         The ProtectionDomain of the class, or <tt>null</tt>.
       *
       * @return  The <tt>Class</tt> object created from the data,
       *          and optional <tt>ProtectionDomain</tt>.
       *
       * @throws  ClassFormatError
       *          If the data did not contain a valid class.
       *
       * @throws  NoClassDefFoundError
       *          If <tt>name</tt> is not equal to the <a href="#name">binary
       *          name</a> of the class specified by <tt>b</tt>
       *
       * @throws  SecurityException
       *          If an attempt is made to add this class to a package that
       *          contains classes that were signed by a different set of
       *          certificates than this class, or if <tt>name</tt> begins with
       *          "<tt>java.</tt>".
       *
       * @see      #defineClass(String, byte[], int, int, ProtectionDomain)
       *
       * @since  1.5
       */
      protected final Class<?> defineClass(String name, java.nio.ByteBuffer b,
                                           ProtectionDomain protectionDomain)
          throws ClassFormatError
      {
          throw new UnsupportedOperationException("can't load this type of class file");
      }
  
      /**
       * Links the specified class.  This (misleadingly named) method may be
       * used by a class loader to link a class.  If the class <tt>c</tt> has
       * already been linked, then this method simply returns. Otherwise, the
       * class is linked as described in the "Execution" chapter of
       * <cite>The Java&trade; Language Specification</cite>.
       *
       * @param  c
       *         The class to link
       *
       * @throws  NullPointerException
       *          If <tt>c</tt> is <tt>null</tt>.
       *
       * @see  #defineClass(String, byte[], int, int)
       */
      protected final void resolveClass(Class<?> c) {
      }
  
      /**
       * Finds a class with the specified <a href="#name">binary name</a>,
       * loading it if necessary.
       *
       * <p> This method loads the class through the system class loader (see
       * {@link #getSystemClassLoader()}).  The <tt>Class</tt> object returned
       * might have more than one <tt>ClassLoader</tt> associated with it.
       * Subclasses of <tt>ClassLoader</tt> need not usually invoke this method,
       * because most class loaders need to override just {@link
       * #findClass(String)}.  </p>
       *
       * @param  name
       *         The <a href="#name">binary name</a> of the class
       *
       * @return  The <tt>Class</tt> object for the specified <tt>name</tt>
       *
       * @throws  ClassNotFoundException
       *          If the class could not be found
       *
       * @see  #ClassLoader(ClassLoader)
       * @see  #getParent()
       */
      protected final Class<?> findSystemClass(String name)
          throws ClassNotFoundException
      {
          return Class.forName(name, false, getSystemClassLoader());
      }
  
      /**
       * Returns a class loaded by the bootstrap class loader;
       * or return null if not found.
       */
      private Class<?> findBootstrapClassOrNull(String name)
      {
          return null;
      }
  
      /**
       * Returns the class with the given <a href="#name">binary name</a> if this
       * loader has been recorded by the Java virtual machine as an initiating
       * loader of a class with that <a href="#name">binary name</a>.  Otherwise
       * <tt>null</tt> is returned.
       *
       * @param  name
       *         The <a href="#name">binary name</a> of the class
       *
       * @return  The <tt>Class</tt> object, or <tt>null</tt> if the class has
       *          not been loaded
       *
       * @since  1.1
       */
      protected final Class<?> findLoadedClass(String name) {
          ClassLoader loader;
          if (this == BootClassLoader.getInstance())
              loader = null;
          else
              loader = this;
          return VMClassLoader.findLoadedClass(loader, name);
      }
  
      /**
       * Sets the signers of a class.  This should be invoked after defining a
       * class.
       *
       * @param  c
       *         The <tt>Class</tt> object
       *
       * @param  signers
       *         The signers for the class
       *
       * @since  1.1
       */
      protected final void setSigners(Class<?> c, Object[] signers) {
      }
  
  
      // -- Resource --
  
      /**
       * Finds the resource with the given name.  A resource is some data
       * (images, audio, text, etc) that can be accessed by class code in a way
       * that is independent of the location of the code.
       *
       * <p> The name of a resource is a '<tt>/</tt>'-separated path name that
       * identifies the resource.
       *
       * <p> This method will first search the parent class loader for the
       * resource; if the parent is <tt>null</tt> the path of the class loader
       * built-in to the virtual machine is searched.  That failing, this method
       * will invoke {@link #findResource(String)} to find the resource.  </p>
       *
       * @apiNote When overriding this method it is recommended that an
       * implementation ensures that any delegation is consistent with the {@link
       * #getResources(String) getResources(String)} method.
       *
       * @param  name
       *         The resource name
       *
       * @return  A <tt>URL</tt> object for reading the resource, or
       *          <tt>null</tt> if the resource could not be found or the invoker
       *          doesn't have adequate  privileges to get the resource.
       *
       * @since  1.1
       */
      public URL getResource(String name) {
          URL url;
          if (parent != null) {
              url = parent.getResource(name);
          } else {
              url = getBootstrapResource(name);
          }
          if (url == null) {
              url = findResource(name);
          }
          return url;
      }
  
      /**
       * Finds all the resources with the given name. A resource is some data
       * (images, audio, text, etc) that can be accessed by class code in a way
       * that is independent of the location of the code.
       *
       * <p>The name of a resource is a <tt>/</tt>-separated path name that
       * identifies the resource.
       *
       * <p> The search order is described in the documentation for {@link
       * #getResource(String)}.  </p>
       *
       * @apiNote When overriding this method it is recommended that an
       * implementation ensures that any delegation is consistent with the {@link
       * #getResource(String) getResource(String)} method. This should
       * ensure that the first element returned by the Enumeration's
       * {@code nextElement} method is the same resource that the
       * {@code getResource(String)} method would return.
       *
       * @param  name
       *         The resource name
       *
       * @return  An enumeration of {@link URL <tt>URL</tt>} objects for
       *          the resource.  If no resources could  be found, the enumeration
       *          will be empty.  Resources that the class loader doesn't have
       *          access to will not be in the enumeration.
       *
       * @throws  IOException
       *          If I/O errors occur
       *
       * @see  #findResources(String)
       *
       * @since  1.2
       */
      public Enumeration<URL> getResources(String name) throws IOException {
          @SuppressWarnings("unchecked")
          Enumeration<URL>[] tmp = (Enumeration<URL>[]) new Enumeration<?>[2];
          if (parent != null) {
              tmp[0] = parent.getResources(name);
          } else {
              tmp[0] = getBootstrapResources(name);
          }
          tmp[1] = findResources(name);
  
          return new CompoundEnumeration<>(tmp);
      }
  
      /**
       * Finds the resource with the given name. Class loader implementations
       * should override this method to specify where to find resources.
       *
       * @param  name
       *         The resource name
       *
       * @return  A <tt>URL</tt> object for reading the resource, or
       *          <tt>null</tt> if the resource could not be found
       *
       * @since  1.2
       */
      protected URL findResource(String name) {
          return null;
      }
  
      /**
       * Returns an enumeration of {@link URL <tt>URL</tt>} objects
       * representing all the resources with the given name. Class loader
       * implementations should override this method to specify where to load
       * resources from.
       *
       * @param  name
       *         The resource name
       *
       * @return  An enumeration of {@link URL <tt>URL</tt>} objects for
       *          the resources
       *
       * @throws  IOException
       *          If I/O errors occur
       *
       * @since  1.2
       */
      protected Enumeration<URL> findResources(String name) throws IOException {
          return Collections.emptyEnumeration();
      }
  
      /**
       * Registers the caller as parallel capable.
       * The registration succeeds if and only if all of the following
       * conditions are met:
       * <ol>
       * <li> no instance of the caller has been created</li>
       * <li> all of the super classes (except class Object) of the caller are
       * registered as parallel capable</li>
       * </ol>
       * <p>Note that once a class loader is registered as parallel capable, there
       * is no way to change it back.</p>
       *
       * @return  true if the caller is successfully registered as
       *          parallel capable and false if otherwise.
       *
       * @since   1.7
       */
      @CallerSensitive
      protected static boolean registerAsParallelCapable() {
          return true;
      }
  
      /**
       * Find a resource of the specified name from the search path used to load
       * classes.  This method locates the resource through the system class
       * loader (see {@link #getSystemClassLoader()}).
       *
       * @param  name
       *         The resource name
       *
       * @return  A {@link URL <tt>URL</tt>} object for reading the
       *          resource, or <tt>null</tt> if the resource could not be found
       *
       * @since  1.1
       */
      public static URL getSystemResource(String name) {
          ClassLoader system = getSystemClassLoader();
          if (system == null) {
              return getBootstrapResource(name);
          }
          return system.getResource(name);
      }
  
      /**
       * Finds all resources of the specified name from the search path used to
       * load classes.  The resources thus found are returned as an
       * {@link Enumeration <tt>Enumeration</tt>} of {@link
       * URL <tt>URL</tt>} objects.
       *
       * <p> The search order is described in the documentation for {@link
       * #getSystemResource(String)}.  </p>
       *
       * @param  name
       *         The resource name
       *
       * @return  An enumeration of resource {@link URL <tt>URL</tt>}
       *          objects
       *
       * @throws  IOException
       *          If I/O errors occur
  
       * @since  1.2
       */
      public static Enumeration<URL> getSystemResources(String name)
          throws IOException
      {
          ClassLoader system = getSystemClassLoader();
          if (system == null) {
              return getBootstrapResources(name);
          }
          return system.getResources(name);
      }
  
      /**
       * Find resources from the VM's built-in classloader.
       */
      private static URL getBootstrapResource(String name) {
          return null;
      }
  
      /**
       * Find resources from the VM's built-in classloader.
       */
      private static Enumeration<URL> getBootstrapResources(String name)
          throws IOException
      {
          return null;
      }
  
  
  
      /**
       * Returns an input stream for reading the specified resource.
       *
       * <p> The search order is described in the documentation for {@link
       * #getResource(String)}.  </p>
       *
       * @param  name
       *         The resource name
       *
       * @return  An input stream for reading the resource, or <tt>null</tt>
       *          if the resource could not be found
       *
       * @since  1.1
       */
      public InputStream getResourceAsStream(String name) {
          URL url = getResource(name);
          try {
              return url != null ? url.openStream() : null;
          } catch (IOException e) {
              return null;
          }
      }
  
      /**
       * Open for reading, a resource of the specified name from the search path
       * used to load classes.  This method locates the resource through the
       * system class loader (see {@link #getSystemClassLoader()}).
       *
       * @param  name
       *         The resource name
       *
       * @return  An input stream for reading the resource, or <tt>null</tt>
       *          if the resource could not be found
       *
       * @since  1.1
       */
      public static InputStream getSystemResourceAsStream(String name) {
          URL url = getSystemResource(name);
          try {
              return url != null ? url.openStream() : null;
          } catch (IOException e) {
              return null;
          }
      }
  
  
      // -- Hierarchy --
  
      /**
       * Returns the parent class loader for delegation. Some implementations may
       * use <tt>null</tt> to represent the bootstrap class loader. This method
       * will return <tt>null</tt> in such implementations if this class loader's
       * parent is the bootstrap class loader.
       *
       * <p> If a security manager is present, and the invoker's class loader is
       * not <tt>null</tt> and is not an ancestor of this class loader, then this
       * method invokes the security manager's {@link
       * SecurityManager#checkPermission(java.security.Permission)
       * <tt>checkPermission</tt>} method with a {@link
       * RuntimePermission#RuntimePermission(String)
       * <tt>RuntimePermission("getClassLoader")</tt>} permission to verify
       * access to the parent class loader is permitted.  If not, a
       * <tt>SecurityException</tt> will be thrown.  </p>
       *
       * @return  The parent <tt>ClassLoader</tt>
       *
       * @throws  SecurityException
       *          If a security manager exists and its <tt>checkPermission</tt>
       *          method doesn't allow access to this class loader's parent class
       *          loader.
       *
       * @since  1.2
       */
      @CallerSensitive
      public final ClassLoader getParent() {
          return parent;
      }
  
      // Android-changed: Removed "java.system.class.loader" paragraph.
      /**
       * Returns the system class loader for delegation.  This is the default
       * delegation parent for new <tt>ClassLoader</tt> instances, and is
       * typically the class loader used to start the application.
       *
       * <p> This method is first invoked early in the runtime's startup
       * sequence, at which point it creates the system class loader and sets it
       * as the context class loader of the invoking <tt>Thread</tt>.
       *
       * <p> The default system class loader is an implementation-dependent
       * instance of this class.
       *
       * <p> If a security manager is present, and the invoker's class loader is
       * not <tt>null</tt> and the invoker's class loader is not the same as or
       * an ancestor of the system class loader, then this method invokes the
       * security manager's {@link
       * SecurityManager#checkPermission(java.security.Permission)
       * <tt>checkPermission</tt>} method with a {@link
       * RuntimePermission#RuntimePermission(String)
       * <tt>RuntimePermission("getClassLoader")</tt>} permission to verify
       * access to the system class loader.  If not, a
       * <tt>SecurityException</tt> will be thrown.  </p>
       *
       * @return  The system <tt>ClassLoader</tt> for delegation, or
       *          <tt>null</tt> if none
       *
       * @throws  SecurityException
       *          If a security manager exists and its <tt>checkPermission</tt>
       *          method doesn't allow access to the system class loader.
       *
       * @throws  IllegalStateException
       *          If invoked recursively during the construction of the class
       *          loader specified by the "<tt>java.system.class.loader</tt>"
       *          property.
       *
       * @throws  Error
       *          If the system property "<tt>java.system.class.loader</tt>"
       *          is defined but the named class could not be loaded, the
       *          provider class does not define the required constructor, or an
       *          exception is thrown by that constructor when it is invoked. The
       *          underlying cause of the error can be retrieved via the
       *          {@link Throwable#getCause()} method.
       *
       * @revised  1.4
       */
      @CallerSensitive
      public static ClassLoader getSystemClassLoader() {
          return SystemClassLoader.loader;
      }
  
      // Returns the class's class loader, or null if none.
      static ClassLoader getClassLoader(Class<?> caller) {
          // This can be null if the VM is requesting it
          if (caller == null) {
              return null;
          }
          // Android-changed: Use Class.getClassLoader(); there is no Class.getClassLoader0().
          // // Circumvent security check since this is package-private
          // return caller.getClassLoader0();
          return caller.getClassLoader();
      }
  
      // -- Package --
  
      /**
       * Defines a package by name in this <tt>ClassLoader</tt>.  This allows
       * class loaders to define the packages for their classes. Packages must
       * be created before the class is defined, and package names must be
       * unique within a class loader and cannot be redefined or changed once
       * created.
       *
       * @param  name
       *         The package name
       *
       * @param  specTitle
       *         The specification title
       *
       * @param  specVersion
       *         The specification version
       *
       * @param  specVendor
       *         The specification vendor
       *
       * @param  implTitle
       *         The implementation title
       *
       * @param  implVersion
       *         The implementation version
       *
       * @param  implVendor
       *         The implementation vendor
       *
       * @param  sealBase
       *         If not <tt>null</tt>, then this package is sealed with
       *         respect to the given code source {@link URL
       *         <tt>URL</tt>}  object.  Otherwise, the package is not sealed.
       *
       * @return  The newly defined <tt>Package</tt> object
       *
       * @throws  IllegalArgumentException
       *          If package name duplicates an existing package either in this
       *          class loader or one of its ancestors
       *
       * @since  1.2
       */
      protected Package definePackage(String name, String specTitle,
                                      String specVersion, String specVendor,
                                      String implTitle, String implVersion,
                                      String implVendor, URL sealBase)
          throws IllegalArgumentException
      {
          synchronized (packages) {
              Package pkg = packages.get(name);
              if (pkg != null) {
                  throw new IllegalArgumentException(name);
              }
              pkg = new Package(name, specTitle, specVersion, specVendor,
                                implTitle, implVersion, implVendor,
                                sealBase, this);
              packages.put(name, pkg);
              return pkg;
          }
      }
  
      /**
       * Returns a <tt>Package</tt> that has been defined by this class loader
       * or any of its ancestors.
       *
       * @param  name
       *         The package name
       *
       * @return  The <tt>Package</tt> corresponding to the given name, or
       *          <tt>null</tt> if not found
       *
       * @since  1.2
       */
      protected Package getPackage(String name) {
          Package pkg;
          synchronized (packages) {
              pkg = packages.get(name);
          }
          return pkg;
      }
  
      /**
       * Returns all of the <tt>Packages</tt> defined by this class loader and
       * its ancestors.
       *
       * @return  The array of <tt>Package</tt> objects defined by this
       *          <tt>ClassLoader</tt>
       *
       * @since  1.2
       */
      protected Package[] getPackages() {
          Map<String, Package> map;
          synchronized (packages) {
              map = new HashMap<>(packages);
          }
          Package[] pkgs;
          return map.values().toArray(new Package[map.size()]);
      }
  
  
      // -- Native library access --
  
      /**
       * Returns the absolute path name of a native library.  The VM invokes this
       * method to locate the native libraries that belong to classes loaded with
       * this class loader. If this method returns <tt>null</tt>, the VM
       * searches the library along the path specified as the
       * "<tt>java.library.path</tt>" property.
       *
       * @param  libname
       *         The library name
       *
       * @return  The absolute path of the native library
       *
       * @see  System#loadLibrary(String)
       * @see  System#mapLibraryName(String)
       *
       * @since  1.2
       */
      protected String findLibrary(String libname) {
          return null;
      }
  
      /**
       * Sets the default assertion status for this class loader.  This setting
       * determines whether classes loaded by this class loader and initialized
       * in the future will have assertions enabled or disabled by default.
       * This setting may be overridden on a per-package or per-class basis by
       * invoking {@link #setPackageAssertionStatus(String, boolean)} or {@link
       * #setClassAssertionStatus(String, boolean)}.
       *
       * @param  enabled
       *         <tt>true</tt> if classes loaded by this class loader will
       *         henceforth have assertions enabled by default, <tt>false</tt>
       *         if they will have assertions disabled by default.
       *
       * @since  1.4
       */
      public void setDefaultAssertionStatus(boolean enabled) {
      }
  
      /**
       * Sets the package default assertion status for the named package.  The
       * package default assertion status determines the assertion status for
       * classes initialized in the future that belong to the named package or
       * any of its "subpackages".
       *
       * <p> A subpackage of a package named p is any package whose name begins
       * with "<tt>p.</tt>".  For example, <tt>javax.swing.text</tt> is a
       * subpackage of <tt>javax.swing</tt>, and both <tt>java.util</tt> and
       * <tt>java.lang.reflect</tt> are subpackages of <tt>java</tt>.
       *
       * <p> In the event that multiple package defaults apply to a given class,
       * the package default pertaining to the most specific package takes
       * precedence over the others.  For example, if <tt>javax.lang</tt> and
       * <tt>javax.lang.reflect</tt> both have package defaults associated with
       * them, the latter package default applies to classes in
       * <tt>javax.lang.reflect</tt>.
       *
       * <p> Package defaults take precedence over the class loader's default
       * assertion status, and may be overridden on a per-class basis by invoking
       * {@link #setClassAssertionStatus(String, boolean)}.  </p>
       *
       * @param  packageName
       *         The name of the package whose package default assertion status
       *         is to be set. A <tt>null</tt> value indicates the unnamed
       *         package that is "current"
       *         (see section 7.4.2 of
       *         <cite>The Java&trade; Language Specification</cite>.)
       *
       * @param  enabled
       *         <tt>true</tt> if classes loaded by this classloader and
       *         belonging to the named package or any of its subpackages will
       *         have assertions enabled by default, <tt>false</tt> if they will
       *         have assertions disabled by default.
       *
       * @since  1.4
       */
      public void setPackageAssertionStatus(String packageName,
                                            boolean enabled) {
      }
  
      /**
       * Sets the desired assertion status for the named top-level class in this
       * class loader and any nested classes contained therein.  This setting
       * takes precedence over the class loader's default assertion status, and
       * over any applicable per-package default.  This method has no effect if
       * the named class has already been initialized.  (Once a class is
       * initialized, its assertion status cannot change.)
       *
       * <p> If the named class is not a top-level class, this invocation will
       * have no effect on the actual assertion status of any class. </p>
       *
       * @param  className
       *         The fully qualified class name of the top-level class whose
       *         assertion status is to be set.
       *
       * @param  enabled
       *         <tt>true</tt> if the named class is to have assertions
       *         enabled when (and if) it is initialized, <tt>false</tt> if the
       *         class is to have assertions disabled.
       *
       * @since  1.4
       */
      public void setClassAssertionStatus(String className, boolean enabled) {
      }
  
      /**
       * Sets the default assertion status for this class loader to
       * <tt>false</tt> and discards any package defaults or class assertion
       * status settings associated with the class loader.  This method is
       * provided so that class loaders can be made to ignore any command line or
       * persistent assertion status settings and "start with a clean slate."
       *
       * @since  1.4
       */
      public void clearAssertionStatus() {
          /*
           * Whether or not "Java assertion maps" are initialized, set
           * them to empty maps, effectively ignoring any present settings.
           */
      }
  }
  
  
  