Spec-Zone .ru
спецификации, руководства, описания, API
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There are two categories of methods provided in
Class
for accessing fields, methods, and constructors: methods which enumerate these members and methods which search for particular members. Also there are distinct methods for accessing members declared directly on the class versus methods which search the superinterfaces and superclasses for inherited members. The following tables provide a summary of all the member-locating methods and their characteristics.
Class |
List of members? | Inherited members? | Private members? |
---|---|---|---|
getDeclaredField() |
no | no | yes |
getField() |
no | yes | no |
getDeclaredFields() |
yes | no | yes |
getFields() |
yes | yes | no |
Class |
List of members? | Inherited members? | Private members? |
---|---|---|---|
getDeclaredMethod() |
no | no | yes |
getMethod() |
no | yes | no |
getDeclaredMethods() |
yes | no | yes |
getMethods() |
yes | yes | no |
Class |
List of members? | Inherited members? | Private members? |
---|---|---|---|
getDeclaredConstructor() |
no | N/A1 | yes |
getConstructor() |
no | N/A1 | no |
getDeclaredConstructors() |
yes | N/A1 | yes |
getConstructors() |
yes | N/A1 | no |
1 Constructors are not inherited.
Given a class name and an indication of which members are of interest, the
example uses the ClassSpy
get*s()
methods to determine the list of all public elements, including any which are inherited.
import java.lang.reflect.Constructor; import java.lang.reflect.Field; import java.lang.reflect.Method; import java.lang.reflect.Member; import static java.lang.System.out; enum ClassMember { CONSTRUCTOR, FIELD, METHOD, CLASS, ALL } public class ClassSpy { public static void main(String... args) { try { Class<?> c = Class.forName(args[0]); out.format("Class:%n %s%n%n", c.getCanonicalName()); Package p = c.getPackage(); out.format("Package:%n %s%n%n", (p != null ? p.getName() : "-- No Package --")); for (int i = 1; i < args.length; i++) { switch (ClassMember.valueOf(args[i])) { case CONSTRUCTOR: printMembers(c.getConstructors(), "Constructor"); break; case FIELD: printMembers(c.getFields(), "Fields"); break; case METHOD: printMembers(c.getMethods(), "Methods"); break; case CLASS: printClasses(c); break; case ALL: printMembers(c.getConstructors(), "Constuctors"); printMembers(c.getFields(), "Fields"); printMembers(c.getMethods(), "Methods"); printClasses(c); break; default: assert false; } } // production code should handle these exceptions more gracefully } catch (ClassNotFoundException x) { x.printStackTrace(); } } private static void printMembers(Member[] mbrs, String s) { out.format("%s:%n", s); for (Member mbr : mbrs) { if (mbr instanceof Field) out.format(" %s%n", ((Field)mbr).toGenericString()); else if (mbr instanceof Constructor) out.format(" %s%n", ((Constructor)mbr).toGenericString()); else if (mbr instanceof Method) out.format(" %s%n", ((Method)mbr).toGenericString()); } if (mbrs.length == 0) out.format(" -- No %s --%n", s); out.format("%n"); } private static void printClasses(Class<?> c) { out.format("Classes:%n"); Class<?>[] clss = c.getClasses(); for (Class<?> cls : clss) out.format(" %s%n", cls.getCanonicalName()); if (clss.length == 0) out.format(" -- No member interfaces, classes, or enums --%n"); out.format("%n"); } }
This example is relatively compact; however the printMembers()
method is slightly awkward due to the fact that the
java.lang.reflect.Member
interface has existed since the earliest implementations of reflection and it could not be modified to include the more useful getGenericString()
method when generics were introduced. The only alternatives are to test and cast as shown, replace this method with printConstructors()
, printFields()
, and printMethods()
, or to be satisfied with the relatively spare results of
Member.getName()
Samples of the output and their interpretation follows. User input is in italics.
$ java ClassSpy java.lang.ClassCastException CONSTRUCTOR Class: java.lang.ClassCastException Package: java.lang Constructor: public java.lang.ClassCastException() public java.lang.ClassCastException(java.lang.String)
Since constructors are not inherited, the exception chaining mechanism constructors (those with a
Throwable
RuntimeException
$ java ClassSpy java.nio.channels.ReadableByteChannel METHOD Class: java.nio.channels.ReadableByteChannel Package: java.nio.channels Methods: public abstract int java.nio.channels.ReadableByteChannel.read (java.nio.ByteBuffer) throws java.io.IOException public abstract void java.nio.channels.Channel.close() throws java.io.IOException public abstract boolean java.nio.channels.Channel.isOpen()
The interface
java.nio.channels.ReadableByteChannel
read()
get*s()
with getDeclared*s()
.
$ java ClassSpy ClassMember FIELD METHOD Class: ClassMember Package: -- No Package -- Fields: public static final ClassMember ClassMember.CONSTRUCTOR public static final ClassMember ClassMember.FIELD public static final ClassMember ClassMember.METHOD public static final ClassMember ClassMember.CLASS public static final ClassMember ClassMember.ALL Methods: public static ClassMember ClassMember.valueOf(java.lang.String) public static ClassMember[] ClassMember.values() public final int java.lang.Enum.hashCode() public final int java.lang.Enum.compareTo(E) public int java.lang.Enum.compareTo(java.lang.Object) public final java.lang.String java.lang.Enum.name() public final boolean java.lang.Enum.equals(java.lang.Object) public java.lang.String java.lang.Enum.toString() public static <T> T java.lang.Enum.valueOf (java.lang.Class<T>,java.lang.String) public final java.lang.Class<E> java.lang.Enum.getDeclaringClass() public final int java.lang.Enum.ordinal() public final native java.lang.Class<?> java.lang.Object.getClass() public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException public final void java.lang.Object.wait() hrows java.lang.InterruptedException public final native void java.lang.Object.notify() public final native void java.lang.Object.notifyAll()
In the fields portion of these results, enum constants are listed. While these are technically fields, it might be useful to distinguish them from other fields. This example could be modified to use
java.lang.reflect.Field.isEnumConstant()
example in a later section of this trail, Examining Enums, contains a possible implementation.EnumSpy
In the methods section of the output, observe that the method name includes the name of the declaring class. Thus, the toString()
method is implemented by
Enum
, not inherited from
Object
Field.getDeclaringClass()
if (mbr instanceof Field) { Field f = (Field)mbr; out.format(" %s%n", f.toGenericString()); out.format(" -- declared in: %s%n", f.getDeclaringClass()); }