/* 
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 java.lang;

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.nio.ByteBuffer;
import java.security.ProtectionDomain;
import java.util.Enumeration;

/**
 * Loads classes and resources from a repository. One or more class loaders are
 * installed at runtime. These are consulted whenever the runtime system needs a
 * specific class that is not yet available in-memory. Typically, class loaders
 * are grouped into a tree where child class loaders delegate all requests to
 * parent class loaders. Only if the parent class loader cannot satisfy the
 * request, the child class loader itself tries to handle it.
 * <p>
 * {@code ClassLoader} is an abstract class that implements the common
 * infrastructure required by all class loaders.
 * </p>
 *
 * @see Class
 * @since 1.0
 */
public abstract class ClassLoader {

    /*
     * This class must be implemented by the VM. The documented methods and
     * natives must be implemented to support other provided class
     * implementations in this package.
     */

    /**
     * The 'System' ClassLoader; also known as the bootstrap ClassLoader.
     * 
     * @see #getSystemClassLoader()
     */
    static ClassLoader systemClassLoader;

    /**
     * <p>
     * TODO Document this method.
     * </p>
     */
    static final void initializeClassLoaders() {
        return;
    }

    /**
     * Returns the system class loader. This is the parent for new
     * {@code ClassLoader} instances and is typically the class loader used to
     * start the application. If a security manager is present and the caller's
     * class loader is neither {@code null} nor the same as or an ancestor of
     * the system class loader, then this method calls the security manager's
     * checkPermission method with a RuntimePermission("getClassLoader")
     * permission to ensure that it is ok to access the system class loader. If
     * not, a {@code SecurityException} is thrown.
     *
     * @return the system class loader.
     * @throws SecurityException
     *             if a security manager exists and it does not allow access to
     *             the system class loader.
     */
    public static ClassLoader getSystemClassLoader() {
        return null;
    }

    /**
     * Finds the URL of the resource with the specified name. The system class
     * loader's resource lookup algorithm is used to find the resource.
     *
     * @return the {@code URL} object for the requested resource or {@code null}
     *         if the resource can not be found.
     * @param resName
     *            the name of the resource to find.
     * @see Class#getResource
     */
    public static URL getSystemResource(String resName) {
        return null;
    }

    /**
     * Returns an enumeration of URLs for the resource with the specified name.
     * The system class loader's resource lookup algorithm is used to find the
     * resource.
     *
     * @return an enumeration of {@code URL} objects containing the requested
     *         resources.
     * @param resName
     *            the name of the resource to find.
     * @throws IOException
     *             if an I/O error occurs.
     */
    public static Enumeration<URL> getSystemResources(String resName)
            throws IOException {
        return null;
    }

    /**
     * Returns a stream for the resource with the specified name. The system
     * class loader's resource lookup algorithm is used to find the resource.
     * Basically, the contents of the java.class.path are searched in order,
     * looking for a path which matches the specified resource.
     *
     * @return a stream for the resource or {@code null}.
     * @param resName
     *            the name of the resource to find.
     * @see Class#getResourceAsStream
     */
    public static InputStream getSystemResourceAsStream(String resName) {
        return null;
    }

    /**
     * Constructs a new instance of this class with the system class loader as
     * its parent.
     *
     * @throws SecurityException
     *             if a security manager exists and it does not allow the
     *             creation of a new {@code ClassLoader}.
     */
    protected ClassLoader() {
        super();
    }

    /**
     * Constructs a new instance of this class with the specified class loader
     * as its parent.
     *
     * @param parentLoader
     *            The {@code ClassLoader} to use as the new class loader's
     *            parent.
     * @throws SecurityException
     *             if a security manager exists and it does not allow the
     *             creation of new a new {@code ClassLoader}.
     */
    protected ClassLoader(ClassLoader parentLoader) {
        super();
    }

    /**
     * Constructs a new class from an array of bytes containing a class
     * definition in class file format.
     *
     * @param classRep
     *            the memory image of a class file.
     * @param offset
     *            the offset into {@code classRep}.
     * @param length
     *            the length of the class file.
     * @return the {@code Class} object created from the specified subset of
     *         data in {@code classRep}.
     * @throws ClassFormatError
     *             if {@code classRep} does not contain a valid class.
     * @throws IndexOutOfBoundsException
     *             if {@code offset < 0}, {@code length < 0} or if
     *             {@code offset + length} is greater than the length of
     *             {@code classRep}.
     * @deprecated Use {@link #defineClass(String, byte[], int, int)}
     */
    @Deprecated
    protected final Class<?> defineClass(byte[] classRep, int offset, int length)
            throws ClassFormatError {
        return null;
    }

    /**
     * Constructs a new class from an array of bytes containing a class
     * definition in class file format.
     *
     * @param className
     *            the expected name of the new class, may be {@code null} if not
     *            known.
     * @param classRep
     *            the memory image of a class file.
     * @param offset
     *            the offset into {@code classRep}.
     * @param length
     *            the length of the class file.
     * @return the {@code Class} object created from the specified subset of
     *         data in {@code classRep}.
     * @throws ClassFormatError
     *             if {@code classRep} does not contain a valid class.
     * @throws IndexOutOfBoundsException
     *             if {@code offset < 0}, {@code length < 0} or if
     *             {@code offset + length} is greater than the length of
     *             {@code classRep}.
     */
    protected final Class<?> defineClass(String className, byte[] classRep,
            int offset, int length) throws ClassFormatError {
        return null;
    }

    /**
     * Constructs a new class from an array of bytes containing a class
     * definition in class file format and assigns the specified protection
     * domain to the new class. If the provided protection domain is
     * {@code null} then a default protection domain is assigned to the class.
     *
     * @param className
     *            the expected name of the new class, may be {@code null} if not
     *            known.
     * @param classRep
     *            the memory image of a class file.
     * @param offset
     *            the offset into {@code classRep}.
     * @param length
     *            the length of the class file.
     * @param protectionDomain
     *            the protection domain to assign to the loaded class, may be
     *            {@code null}.
     * @return the {@code Class} object created from the specified subset of
     *         data in {@code classRep}.
     * @throws ClassFormatError
     *             if {@code classRep} does not contain a valid class.
     * @throws IndexOutOfBoundsException
     *             if {@code offset < 0}, {@code length < 0} or if
     *             {@code offset + length} is greater than the length of
     *             {@code classRep}.
     * @throws NoClassDefFoundError
     *             if {@code className} is not equal to the name of the class
     *             contained in {@code classRep}.
     */
    protected final Class<?> defineClass(String className, byte[] classRep,
            int offset, int length, ProtectionDomain protectionDomain)
            throws java.lang.ClassFormatError {
        return null;
    }

    /**
     * Defines a new class with the specified name, byte code from the byte
     * buffer and the optional protection domain. If the provided protection
     * domain is {@code null} then a default protection domain is assigned to
     * the class.
     *
     * @param name
     *            the expected name of the new class, may be {@code null} if not
     *            known.
     * @param b
     *            the byte buffer containing the byte code of the new class.
     * @param protectionDomain
     *            the protection domain to assign to the loaded class, may be
     *            {@code null}.
     * @return the {@code Class} object created from the data in {@code b}.
     * @throws ClassFormatError
     *             if {@code b} does not contain a valid class.
     * @throws NoClassDefFoundError
     *             if {@code className} is not equal to the name of the class
     *             contained in {@code b}.
     * @since 1.5
     */
    protected final Class<?> defineClass(String name, ByteBuffer b,
            ProtectionDomain protectionDomain) throws ClassFormatError {
        byte[] temp = new byte[b.remaining()];
        b.get(temp);
        return defineClass(name, temp, 0, temp.length, protectionDomain);
    }

    /**
     * Overridden by subclasses, throws a {@code ClassNotFoundException} by
     * default. This method is called by {@code loadClass} after the parent
     * {@code ClassLoader} has failed to find a loaded class of the same name.
     *
     * @param className
     *            the name of the class to look for.
     * @return the {@code Class} object that is found.
     * @throws ClassNotFoundException
     *             if the class cannot be found.
     */
    protected Class<?> findClass(String className)
            throws ClassNotFoundException {
        return null;
    }

    /**
     * Returns the class with the specified name if it has already been loaded
     * by the virtual machine or {@code null} if it has not yet been loaded.
     *
     * @param className
     *            the name of the class to look for.
     * @return the {@code Class} object or {@code null} if the requested class
     *         has not been loaded.
     */
    protected final Class<?> findLoadedClass(String className) {
        return null;
    }

    /**
     * Finds the class with the specified name, loading it using the system
     * class loader if necessary.
     *
     * @param className
     *            the name of the class to look for.
     * @return the {@code Class} object with the requested {@code className}.
     * @throws ClassNotFoundException
     *             if the class can not be found.
     */
    protected final Class<?> findSystemClass(String className)
            throws ClassNotFoundException {
        return null;
    }

    /**
     * Returns this class loader's parent.
     *
     * @return this class loader's parent or {@code null}.
     * @throws SecurityException
     *             if a security manager exists and it does not allow to
     *             retrieve the parent class loader.
     */
    public final ClassLoader getParent() {
        return null;
    }

    /**
     * Returns an URL which can be used to access the resource described by
     * resName, using the class loader's resource lookup algorithm. The default
     * behavior is just to return null.
     *
     * @param resName
     *            the name of the resource to find.
     * @return the {@code URL} object for the requested resource or {@code null}
     *         if either the resource can not be found or a security manager
     *         does not allow to access the resource.
     * @see Class#getResource
     */
    public URL getResource(String resName) {
        return null;
    }

    /**
     * Returns an Enumeration of URL which can be used to access the resources
     * described by resName, using the class loader's resource lookup algorithm.
     * The default behavior is just to return an empty Enumeration.
     *
     * @return an enumeration of {@code URL} objects for the requested resource.
     * @param resName
     *            the name of the resource to find.
     * @throws IOException
     *             if an I/O error occurs.
     */
    public Enumeration<URL> getResources(String resName) throws IOException {
        return null;
    }

    /**
     * Returns a stream on a resource found by looking up resName using the
     * class loader's resource lookup algorithm. The default behavior is just to
     * return null.
     *
     * @return a stream for the resource or {@code null} if either the resource
     *         can not be found or a security manager does not allow to access
     *         the resource.
     * @param resName
     *            the name of the resource to find.
     * @see Class#getResourceAsStream
     */
    public InputStream getResourceAsStream(String resName) {
        return null;
    }

    /**
     * Loads the class with the specified name. Invoking this method is
     * equivalent to calling {@code loadClass(className, false)}.
     *
     * @return the {@code Class} object.
     * @param className
     *            the name of the class to look for.
     * @throws ClassNotFoundException
     *             if the class can not be found.
     */
    public Class<?> loadClass(String className) throws ClassNotFoundException {
        return null;
    }

    /**
     * Loads the class with the specified name, optionally linking it after
     * loading. The following steps are performed:
     * <ol>
     * <li> Call {@link #findLoadedClass(String)} to determine if the requested
     * class has already been loaded.</li>
     * <li>If the class has not yet been loaded: Invoke this method on the
     * parent class loader.</li>
     * <li>If the class has still not been loaded: Call
     * {@link #findClass(String)} to find the class.</li>
     * </ol>
     *
     * @return the {@code Class} object.
     * @param className
     *            the name of the class to look for.
     * @param resolve
     *            Indicates if the class should be resolved after loading. This
     *            parameter is ignored on the Android reference implementation;
     *            classes are not resolved.
     * @throws ClassNotFoundException
     *             if the class can not be found.
     */
    protected Class<?> loadClass(String className, boolean resolve)
            throws ClassNotFoundException {
        return null;
    }

    /**
     * Forces a class to be linked (initialized). If the class has already been
     * linked this operation has no effect.
     *
     * @param clazz
     *            the class to link.
     */
    protected final void resolveClass(Class<?> clazz) {
        return;
    }

    /**
     * Indicates whether this class loader is the system class loader. This
     * method must be provided by the virtual machine vendor, as it is used by
     * other provided class implementations in this package. A sample
     * implementation of this method is provided by the reference
     * implementation. This method is used by
     * SecurityManager.classLoaderDepth(), currentClassLoader() and
     * currentLoadedClass(). Returns true if the receiver is a system class
     * loader.
     * <p>
     * Note that this method has package visibility only. It is defined here to
     * avoid the security manager check in getSystemClassLoader, which would be
     * required to implement this method anywhere else.
     *
     * @return {@code true} if the receiver is a system class loader
     * @see Class#getClassLoaderImpl()
     */
    final boolean isSystemClassLoader() {
        return false;
    }

    /**
     * Returns true if the receiver is ancestor of another class loader. It also
     * returns true if the two class loader are equal.
     * <p>
     * Note that this method has package visibility only. It is defined here to
     * avoid the security manager check in getParent, which would be required to
     * implement this method anywhere else. The method is also required in other
     * places where class loaders are accesses.
     *
     * @param child
     *            A child candidate
     * @return {@code true} if the receiver is ancestor of, or equal to,
     *         the parameter
     */
    final boolean isAncestorOf(ClassLoader child) {
        return false;
    }

    /**
     * Finds the URL of the resource with the specified name. This
     * implementation just returns {@code null}; it should be overridden in
     * subclasses.
     *
     * @param resName
     *            the name of the resource to find.
     * @return the {@code URL} object for the requested resource.
     */
    protected URL findResource(String resName) {
        return null;
    }

    /**
     * Finds an enumeration of URLs for the resource with the specified name.
     * This implementation just returns an empty {@code Enumeration}; it should
     * be overridden in subclasses.
     *
     * @param resName
     *            the name of the resource to find.
     * @return an enumeration of {@code URL} objects for the requested resource.
     * @throws IOException
     *             if an I/O error occurs.
     */
    protected Enumeration<URL> findResources(String resName) throws IOException {
        return null;
    }

    /**
     * Returns the absolute path of the file containing the library with the
     * specified name, or {@code null}. If this method returns {@code null} then
     * the virtual machine searches the directories specified by the system
     * property "java.library.path".
     *
     * @param libName
     *            the name of the library to find.
     * @return the absolute path of the library.
     */
    protected String findLibrary(String libName) {
        return null;
    }

    /**
     * Returns the package with the specified name. Package information is
     * searched in this class loader.
     *
     * @param name
     *            the name of the package to find.
     * @return the package with the requested name; {@code null} if the package
     *         can not be found.
     */
    protected Package getPackage(String name) {
        return null;
    }

    /**
     * Returns all the packages known to this class loader.
     *
     * @return an array with all packages known to this class loader.
     */
    protected Package[] getPackages() {
        return null;
    }

    /**
     * Defines and returns a new {@code Package} using the specified
     * information. If {@code sealBase} is {@code null}, the package is left
     * unsealed. Otherwise, the package is sealed using this URL.
     *
     * @param name
     *            the name of the package.
     * @param specTitle
     *            the title of the specification.
     * @param specVersion
     *            the version of the specification.
     * @param specVendor
     *            the vendor of the specification.
     * @param implTitle
     *            the implementation title.
     * @param implVersion
     *            the implementation version.
     * @param implVendor
     *            the specification vendor.
     * @param sealBase
     *            the URL used to seal this package or {@code null} to leave the
     *            package unsealed.
     * @return the {@code Package} object that has been created.
     * @throws IllegalArgumentException
     *             if a package with the specified name already exists.
     */
    protected Package definePackage(String name, String specTitle,
            String specVersion, String specVendor, String implTitle,
            String implVersion, String implVendor, URL sealBase)
            throws IllegalArgumentException {
        return null;
    }

    /**
     * Gets the signers of the specified class.
     *
     * @param c
     *            the {@code Class} object for which to get the signers.
     * @return signers the signers of {@code c}.
     */
    final Object[] getSigners(Class<?> c) {
        return null;
    }

    /**
     * Sets the signers of the specified class.
     *
     * @param c
     *            the {@code Class} object for which to set the signers.
     * @param signers
     *            the signers for {@code c}.
     */
    protected final void setSigners(Class<?> c, Object[] signers) {
        return;
    }

    /**
     * <p>
     * This must be provided by the VM vendor. It is used by
     * SecurityManager.checkMemberAccess() with depth = 3. Note that
     * checkMemberAccess() assumes the following stack when called:<br>
     * </p>
     * 
     * <pre>
     *          &lt; user code &amp;gt; &lt;- want this class
     *          Class.getDeclared*();
     *          Class.checkMemberAccess();
     *          SecurityManager.checkMemberAccess(); &lt;- current frame
     * </pre>
     * 
     * <p>
     * Returns the ClassLoader of the method (including natives) at the
     * specified depth on the stack of the calling thread. Frames representing
     * the VM implementation of java.lang.reflect are not included in the list.
     * </p>
     * Notes:
     * <ul>
     * <li>This method operates on the defining classes of methods on stack.
     * NOT the classes of receivers.</li>
     * <li>The item at depth zero is the caller of this method</li>
     * </ul>
     * 
     * @param depth
     *            the stack depth of the requested ClassLoader
     * @return the ClassLoader at the specified depth
     */
    static final ClassLoader getStackClassLoader(int depth) {
        return null;
    }

    /**
     * This method must be included, as it is used by System.load(),
     * System.loadLibrary(). The reference implementation of this method uses
     * the getStackClassLoader() method. Returns the ClassLoader of the method
     * that called the caller. i.e. A.x() calls B.y() calls callerClassLoader(),
     * A's ClassLoader will be returned. Returns null for the bootstrap
     * ClassLoader.
     * 
     * @return a ClassLoader or null for the bootstrap ClassLoader
     */
    static ClassLoader callerClassLoader() {
        return null;
    }

    /**
     * This method must be provided by the VM vendor, as it is called by
     * java.lang.System.loadLibrary(). System.loadLibrary() cannot call
     * Runtime.loadLibrary() because this method loads the library using the
     * ClassLoader of the calling method. Loads and links the library specified
     * by the argument.
     * 
     * @param libName
     *            the name of the library to load
     * @param loader
     *            the classloader in which to load the library
     * @throws UnsatisfiedLinkError
     *             if the library could not be loaded
     * @throws SecurityException
     *             if the library was not allowed to be loaded
     */
    static void loadLibraryWithClassLoader(String libName, ClassLoader loader) {
        return;
    }

    /**
     * This method must be provided by the VM vendor, as it is called by
     * java.lang.System.load(). System.load() cannot call Runtime.load() because
     * the library is loaded using the ClassLoader of the calling method. Loads
     * and links the library specified by the argument. No security check is
     * done.
     * 
     * @param libName
     *            the name of the library to load
     * @param loader
     *            the classloader in which to load the library
     * @param libraryPath
     *            the library path to search, or null
     * @throws UnsatisfiedLinkError
     *             if the library could not be loaded
     */
    static void loadLibraryWithPath(String libName, ClassLoader loader,
            String libraryPath) {
        return;
    }

    /**
     * Sets the assertion status of the class with the specified name.
     *
     * @param cname
     *            the name of the class for which to set the assertion status.
     * @param enable
     *            the new assertion status.
     */
    public void setClassAssertionStatus(String cname, boolean enable) {
        return;
    }

    /**
     * Sets the assertion status of the package with the specified name.
     *
     * @param pname
     *            the name of the package for which to set the assertion status.
     * @param enable
     *            the new assertion status.
     */
    public void setPackageAssertionStatus(String pname, boolean enable) {
        return;
    }

    /**
     * Sets the default assertion status for this class loader.
     *
     * @param enable
     *            the new assertion status.
     */
    public void setDefaultAssertionStatus(boolean enable) {
        return;
    }

    /**
     * Sets the default assertion status for this class loader to {@code false}
     * and removes any package default and class assertion status settings.
     */
    public void clearAssertionStatus() {
        return;
    }

    /**
     * Returns the assertion status of the named class Returns the assertion
     * status of the class or nested class if it has been set. Otherwise returns
     * the assertion status of its package or superpackage if that has been set.
     * Otherwise returns the default assertion status. Returns 1 for enabled and
     * 0 for disabled.
     * 
     * @return the assertion status.
     * @param cname
     *            the name of class.
     */
    boolean getClassAssertionStatus(String cname) {
        return false;
    }

    /**
     * Returns the assertion status of the named package Returns the assertion
     * status of the named package or superpackage if that has been set.
     * Otherwise returns the default assertion status. Returns 1 for enabled and
     * 0 for disabled.
     * 
     * @return the assertion status.
     * @param pname
     *            the name of package.
     */
    boolean getPackageAssertionStatus(String pname) {
        return false;
    }

    /**
     * Returns the default assertion status
     * 
     * @return the default assertion status.
     */
    boolean getDefaultAssertionStatus() {
        return false;
    }
}