门面模式

4.Facade Pattern(Provide a unified interface to a set of interfaces in a subsystem.Facade defines a higher-level interface that makes the subsystem easier to    　　use)--门面模式:要求一个子系统的外部与其内部的通信必须通过一个统一的对象进行。门面模式提供一个高层次的接口，使得子系统更易于使用

JDK中代码样例:

package java.lang;

import java.lang.reflect.AnnotatedElement;
import java.lang.reflect.Array;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.GenericDeclaration;
import java.lang.reflect.Member;
import java.lang.reflect.Field;
import java.lang.reflect.Executable;
import java.lang.reflect.Method;
import java.lang.reflect.Constructor;
import java.lang.reflect.Modifier;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.AnnotatedType;
import java.lang.ref.SoftReference;
import java.io.InputStream;
import java.io.ObjectStreamField;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Set;
import java.util.Map;
import java.util.HashMap;
import java.util.Objects;
import sun.misc.Unsafe;
import sun.reflect.CallerSensitive;
import sun.reflect.ConstantPool;
import sun.reflect.Reflection;
import sun.reflect.ReflectionFactory;
import sun.reflect.generics.factory.CoreReflectionFactory;
import sun.reflect.generics.factory.GenericsFactory;
import sun.reflect.generics.repository.ClassRepository;
import sun.reflect.generics.repository.MethodRepository;
import sun.reflect.generics.repository.ConstructorRepository;
import sun.reflect.generics.scope.ClassScope;
import sun.security.util.SecurityConstants;
import java.lang.annotation.Annotation;
import java.lang.reflect.Proxy;
import sun.reflect.annotation.*;
import sun.reflect.misc.ReflectUtil;

/**
 * Instances of the class {@code Class} represent classes and
 * interfaces in a running Java application.  An enum is a kind of
 * class and an annotation is a kind of interface.  Every array also
 * belongs to a class that is reflected as a {@code Class} object
 * that is shared by all arrays with the same element type and number
 * of dimensions.  The primitive Java types ({@code boolean},
 * {@code byte}, {@code char}, {@code short},
 * {@code int}, {@code long}, {@code float}, and
 * {@code double}), and the keyword {@code void} are also
 * represented as {@code Class} objects.
 *
 * <p> {@code Class} has no public constructor. Instead {@code Class}
 * objects are constructed automatically by the Java Virtual Machine as classes
 * are loaded and by calls to the {@code defineClass} method in the class
 * loader.
 *
 * <p> The following example uses a {@code Class} object to print the
 * class name of an object:
 *
 * <blockquote><pre>
 *     void printClassName(Object obj) {
 *         System.out.println("The class of " + obj +
 *                            " is " + obj.getClass().getName());
 *     }
 * </pre></blockquote>
 *
 * <p> It is also possible to get the {@code Class} object for a named
 * type (or for void) using a class literal.  See Section 15.8.2 of
 * <cite>The Java&trade; Language Specification</cite>.
 * For example:
 *
 * <blockquote>
 *     {@code System.out.println("The name of class Foo is: "+Foo.class.getName());}
 * </blockquote>
 *
 * @param <T> the type of the class modeled by this {@code Class}
 * object.  For example, the type of {@code String.class} is {@code
 * Class<String>}.  Use {@code Class<?>} if the class being modeled is
 * unknown.
 *
 * @author  unascribed
 * @see     java.lang.ClassLoader#defineClass(byte[], int, int)
 * @since   JDK1.0
 */
public final class Class<T> implements java.io.Serializable,
                              GenericDeclaration,
                              Type,
                              AnnotatedElement {
    private static final int ANNOTATION= 0x00002000;
    private static final int ENUM      = 0x00004000;
    private static final int SYNTHETIC = 0x00001000;


    /**
     * Returns the {@code Class} object associated with the class or
     * interface with the given string name, using the given class loader.
     * Given the fully qualified name for a class or interface (in the same
     * format returned by {@code getName}) this method attempts to
     * locate, load, and link the class or interface.  The specified class
     * loader is used to load the class or interface.  If the parameter
     * {@code loader} is null, the class is loaded through the bootstrap
     * class loader.  The class is initialized only if the
     * {@code initialize} parameter is {@code true} and if it has
     * not been initialized earlier.
     *
     * <p> If {@code name} denotes a primitive type or void, an attempt
     * will be made to locate a user-defined class in the unnamed package whose
     * name is {@code name}. Therefore, this method cannot be used to
     * obtain any of the {@code Class} objects representing primitive
     * types or void.
     *
     * <p> If {@code name} denotes an array class, the component type of
     * the array class is loaded but not initialized.
     *
     * <p> For example, in an instance method the expression:
     *
     * <blockquote>
     *  {@code Class.forName("Foo")}
     * </blockquote>
     *
     * is equivalent to:
     *
     * <blockquote>
     *  {@code Class.forName("Foo", true, this.getClass().getClassLoader())}
     * </blockquote>
     *
     * Note that this method throws errors related to loading, linking or
     * initializing as specified in Sections 12.2, 12.3 and 12.4 of <em>The
     * Java Language Specification</em>.
     * Note that this method does not check whether the requested class
     * is accessible to its caller.
     *
     * <p> If the {@code loader} is {@code null}, and a security
     * manager is present, and the caller's class loader is not null, then this
     * method calls the security manager's {@code checkPermission} method
     * with a {@code RuntimePermission("getClassLoader")} permission to
     * ensure it's ok to access the bootstrap class loader.
     *
     * @param name       fully qualified name of the desired class
     * @param initialize if {@code true} the class will be initialized.
     *                   See Section 12.4 of <em>The Java Language Specification</em>.
     * @param loader     class loader from which the class must be loaded
     * @return           class object representing the desired class
     *
     * @exception LinkageError if the linkage fails
     * @exception ExceptionInInitializerError if the initialization provoked
     *            by this method fails
     * @exception ClassNotFoundException if the class cannot be located by
     *            the specified class loader
     *
     * @see       java.lang.Class#forName(String)
     * @see       java.lang.ClassLoader
     * @since     1.2
     */
    @CallerSensitive
    public static Class<?> forName(String name, boolean initialize,
                                   ClassLoader loader)
        throws ClassNotFoundException
    {
        Class<?> caller = null;
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            // Reflective call to get caller class is only needed if a security manager
            // is present.  Avoid the overhead of making this call otherwise.
            caller = Reflection.getCallerClass();
            if (sun.misc.VM.isSystemDomainLoader(loader)) {
                ClassLoader ccl = ClassLoader.getClassLoader(caller);
                if (!sun.misc.VM.isSystemDomainLoader(ccl)) {
                    sm.checkPermission(
                        SecurityConstants.GET_CLASSLOADER_PERMISSION);
                }
            }
        }
        return forName0(name, initialize, loader, caller);
    }
}

说明:以上红色背景的两个接口对外隐藏,处理内部逻辑,只需要调用Class.forName()就可取得Class.