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== A program that displays a class synopsis for the named class ==



<source lang="java">
/*
* Copyright (c) 2004 David Flanagan. All rights reserved.
* This code is from the book Java Examples in a Nutshell, 3nd Edition.
* It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
* You may study, use, and modify it for any non-commercial purpose,
* including teaching and use in open-source projects.
* You may distribute it non-commercially as long as you retain this notice.
* For a commercial use license, or to purchase the book,
* please visit http://www.davidflanagan.ru/javaexamples3.
*/
//package je3.reflect;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
/** A program that displays a class synopsis for the named class */
public class ShowClass {
/** The main method. Print info about the named class */
public static void main(String[] args) throws ClassNotFoundException {
Class c = Class.forName(args[0]);
print_class(c);
}
/**
* Display the modifiers, name, superclass and interfaces of a class or
* interface. Then go and list all constructors, fields, and methods.
*/
public static void print_class(Class c) {
// Print modifiers, type (class or interface), name and superclass.
if (c.isInterface()) {
// The modifiers will include the "interface" keyword here...
System.out.print(Modifier.toString(c.getModifiers()) + " " + typename(c));
} else if (c.getSuperclass() != null) {
System.out.print(Modifier.toString(c.getModifiers()) + " class " + typename(c) + " extends "
+ typename(c.getSuperclass()));
} else {
System.out.print(Modifier.toString(c.getModifiers()) + " class " + typename(c));
}
// Print interfaces or super-interfaces of the class or interface.
Class[] interfaces = c.getInterfaces();
if ((interfaces != null) && (interfaces.length > 0)) {
if (c.isInterface())
System.out.print(" extends ");
else
System.out.print(" implements ");
for (int i = 0; i < interfaces.length; i++) {
if (i > 0)
System.out.print(", ");
System.out.print(typename(interfaces[i]));
}
}
System.out.println(" {"); // Begin class member listing.
// Now look up and display the members of the class.
System.out.println(" // Constructors");
Constructor[] constructors = c.getDeclaredConstructors();
for (int i = 0; i < constructors.length; i++)
// Display constructors.
print_method_or_constructor(constructors[i]);
System.out.println(" // Fields");
Field[] fields = c.getDeclaredFields(); // Look up fields.
for (int i = 0; i < fields.length; i++)
// Display them.
print_field(fields[i]);
System.out.println(" // Methods");
Method[] methods = c.getDeclaredMethods(); // Look up methods.
for (int i = 0; i < methods.length; i++)
// Display them.
print_method_or_constructor(methods[i]);
System.out.println("}"); // End class member listing.
}
/** Return the name of an interface or primitive type, handling arrays. */
public static String typename(Class t) {
String brackets = "";
while (t.isArray()) {
brackets += "[]";
t = t.getComponentType();
}
String name = t.getName();
int pos = name.lastIndexOf(".");
if (pos != -1)
name = name.substring(pos + 1);
return name + brackets;
}
/** Return a string version of modifiers, handling spaces nicely. */
public static String modifiers(int m) {
if (m == 0)
return "";
else
return Modifier.toString(m) + " ";
}
/** Print the modifiers, type, and name of a field */
public static void print_field(Field f) {
System.out.println(" " + modifiers(f.getModifiers()) + typename(f.getType()) + " "
+ f.getName() + ";");
}
/**
* Print the modifiers, return type, name, parameter types and exception type
* of a method or constructor. Note the use of the Member interface to allow
* this method to work with both Method and Constructor objects
*/
public static void print_method_or_constructor(Member member) {
Class returntype = null, parameters[], exceptions[];
if (member instanceof Method) {
Method m = (Method) member;
returntype = m.getReturnType();
parameters = m.getParameterTypes();
exceptions = m.getExceptionTypes();
System.out.print(" " + modifiers(member.getModifiers()) + typename(returntype) + " "
+ member.getName() + "(");
} else {
Constructor c = (Constructor) member;
parameters = c.getParameterTypes();
exceptions = c.getExceptionTypes();
System.out.print(" " + modifiers(member.getModifiers()) + typename(c.getDeclaringClass())
+ "(");
}
for (int i = 0; i < parameters.length; i++) {
if (i > 0)
System.out.print(", ");
System.out.print(typename(parameters[i]));
}
System.out.print(")");
if (exceptions.length > 0)
System.out.print(" throws ");
for (int i = 0; i < exceptions.length; i++) {
if (i > 0)
System.out.print(", ");
System.out.print(typename(exceptions[i]));
}
System.out.println(";");
}
}</source>



== Call Private constructor ==



<source lang="java">
/*
* Copyright (c) 1995 - 2008 Sun Microsystems, Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* - Neither the name of Sun Microsystems nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
class Deny {
private Deny() {
System.out.format("Deny constructor%n");
}
}
public class ConstructorTroubleAccess {
public static void main(String... args) {
try {
Constructor c = Deny.class.getDeclaredConstructor();
// c.setAccessible(true); // solution
c.newInstance();
// production code should handle these exceptions more gracefully
} catch (InvocationTargetException x) {
x.printStackTrace();
} catch (NoSuchMethodException x) {
x.printStackTrace();
} catch (InstantiationException x) {
x.printStackTrace();
} catch (IllegalAccessException x) {
x.printStackTrace();
}
}
}</source>



== Create new instance from Constructor ==



<source lang="java">
/*
* Copyright (c) 1995 - 2008 Sun Microsystems, Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* - Neither the name of Sun Microsystems nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
import static java.lang.System.out;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
class EmailAliases {
private Set<String> aliases;
private EmailAliases(HashMap<String, String> h) {
aliases = h.keySet();
}
public void printKeys() {
out.format("Mail keys:%n");
for (String k : aliases)
out.format(" %s%n", k);
}
}
public class RestoreAliases {
private static Map<String, String> defaultAliases = new HashMap<String, String>();
static {
defaultAliases.put("Duke", "duke@i-love-java");
defaultAliases.put("Fang", "fang@evil-jealous-twin");
}
public static void main(String... args) {
try {
Constructor ctor = EmailAliases.class.getDeclaredConstructor(HashMap.class);
ctor.setAccessible(true);
EmailAliases email = (EmailAliases) ctor.newInstance(defaultAliases);
email.printKeys();
// production code should handle these exceptions more gracefully
} catch (InstantiationException x) {
x.printStackTrace();
} catch (IllegalAccessException x) {
x.printStackTrace();
} catch (InvocationTargetException x) {
x.printStackTrace();
} catch (NoSuchMethodException x) {
x.printStackTrace();
}
}
}</source>



== Demonstrates use of Constructor objects ==



<source lang="java">
/*
* file: ConstructorDemo.java
* package: oreilly.hcj.reflection
*
* This software is granted under the terms of the Common Public License,
* CPL, which may be found at the following URL:
* http://www-124.ibm.ru/developerworks/oss/CPLv1.0.htm
*
* Copyright(c) 2003-2005 by the authors indicated in the @author tags.
* All Rights are Reserved by the various authors.
*
########## DO NOT EDIT ABOVE THIS LINE ########## */

import java.lang.reflect.Constructor;
/**
* Demonstrates use of Constructor objects.
*
* @author
* @version $Revision$
*/
public class ConstructorDemo {
/**
* Run the demo.
*
* @param args Command line arguments.
*/
public static void main(final String[] args) {
try {
final Class[] ARG_TYPES = new Class[] { String.class };
Constructor cst = Integer.class.getConstructor(ARG_TYPES);
System.out.println(cst.newInstance(new Object[] { "45" }));
} catch (final Exception ex) {
ex.printStackTrace();
}
}
}
/* ########## End of File ########## */</source>



== Get a compatible constructor for the given value type ==



<source lang="java">
import java.lang.reflect.Array;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.net.URL;
import java.security.AccessController;
import java.security.CodeSource;
import java.security.PrivilegedAction;
import java.security.ProtectionDomain;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
/*
* JBoss, Home of Professional Open Source
* Copyright 2005, JBoss Inc., and individual contributors as indicated
* by the @authors tag. See the copyright.txt in the distribution for a
* full listing of individual contributors.
*
* This is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This software 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/
public class Main {
/////////////////////////////////////////////////////////////////////////
// Coercion Methods //
/////////////////////////////////////////////////////////////////////////
/**
* Get a compatible constructor for the given value type
*
* @param type Class to look for constructor in
* @param valueType Argument type for constructor
* @return Constructor or null
*/
public static Constructor getCompatibleConstructor(final Class type,
final Class valueType)
{
// first try and find a constructor with the exact argument type
try {
return type.getConstructor(new Class[] { valueType });
}
catch (Exception ignore) {
// if the above failed, then try and find a constructor with
// an compatible argument type
// get an array of compatible types
Class[] types = type.getClasses();
for (int i=0; i<types.length; i++) {
try {
return type.getConstructor(new Class[] { types[i] });
}
catch (Exception ignore2) {}
}
}
// if we get this far, then we can"t find a compatible constructor
return null;
}
}</source>



== Get all constructors or by parameters ==



<source lang="java">
import java.lang.reflect.Constructor;
public class GetConstructor {
public static void main(String[] args) {
Constructor[] cs = String.class.getConstructors();
for(int i=0;i<cs.length;i++){
System.out.println(cs[i]);
}
try {
Constructor c = String.class.getConstructor(new Class[]{String.class});
System.out.println(c);
} catch (SecurityException e) {
e.printStackTrace();
} catch (NoSuchMethodException e) {
e.printStackTrace();
}
}
}</source>



== Get constructor by parameter type ==



<source lang="java">
/*
* Copyright (c) 1995 - 2008 Sun Microsystems, Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* - Neither the name of Sun Microsystems nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
import static java.lang.System.out;
import java.lang.reflect.InvocationTargetException;
public class ConstructorTroubleAgain {
public ConstructorTroubleAgain() {
}
public ConstructorTroubleAgain(Integer i) {
}
public ConstructorTroubleAgain(Object o) {
out.format("Constructor passed Object%n");
}
public ConstructorTroubleAgain(String s) {
out.format("Constructor passed String%n");
}
public static void main(String... args) {
String argType = (args.length == 0 ? "" : args[0]);
try {
Class<?> c = Class.forName("ConstructorTroubleAgain");
if ("".equals(argType)) {
// IllegalArgumentException: wrong number of arguments
Object o = c.getConstructor().newInstance("foo");
} else if ("int".equals(argType)) {
// NoSuchMethodException - looking for int, have Integer
Object o = c.getConstructor(int.class);
} else if ("Object".equals(argType)) {
// newInstance() does not perform method resolution
Object o = c.getConstructor(Object.class).newInstance("foo");
} else {
assert false;
}
// production code should handle these exceptions more gracefully
} catch (ClassNotFoundException x) {
x.printStackTrace();
} catch (NoSuchMethodException x) {
x.printStackTrace();
} catch (InvocationTargetException x) {
x.printStackTrace();
} catch (InstantiationException x) {
x.printStackTrace();
} catch (IllegalAccessException x) {
x.printStackTrace();
}
}
}</source>



== Getting a Constructor of a Class Object: By obtaining a list of all Constructors object ==



<source lang="java">
import java.lang.reflect.Constructor;
public class Main {
public static void main(String[] argv) throws Exception {
Constructor[] cons = String.class.getDeclaredConstructors();
for (int i = 0; i < cons.length; i++) {
Class[] paramTypes = cons[i].getParameterTypes();
System.out.println(cons[i]);
}
}
}</source>



== Getting a Constructor of a Class Object: By obtaining a particular Constructor object. ==



<source lang="java">
import java.lang.reflect.Constructor;
public class Main {
public static void main(String[] argv) throws Exception {
Constructor con = java.awt.Point.class.getConstructor(new Class[] { int.class, int.class });
System.out.println(con);
}
}</source>



== Has Declared Constructor ==



<source lang="java">
import java.lang.reflect.Constructor;
public class ReflectionUtils {
public static boolean hasDeclaredConstructor(Class targetClass, Class[] partypes) {
Constructor constructor = null;
try {
constructor = targetClass.getConstructor(partypes);
}catch (Exception e) {
e.printStackTrace();
}
return constructor != null;
}

}</source>



== Invoke a constructor which throws Exception ==



<source lang="java">
/*
* Copyright (c) 1995 - 2008 Sun Microsystems, Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* - Neither the name of Sun Microsystems nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
import static java.lang.System.err;
import java.lang.reflect.InvocationTargetException;
public class ConstructorTroubleToo {
public ConstructorTroubleToo() {
throw new RuntimeException("exception in constructor");
}
public static void main(String... args) {
try {
Class<?> c = Class.forName("ConstructorTroubleToo");
// Method propagetes any exception thrown by the constructor (including checked exceptions).
if (args.length > 0 && args[0].equals("class")) {
Object o = c.newInstance();
} else {
Object o = c.getConstructor().newInstance();
}
// production code should handle these exceptions more gracefully
} catch (ClassNotFoundException x) {
x.printStackTrace();
} catch (InstantiationException x) {
x.printStackTrace();
} catch (IllegalAccessException x) {
x.printStackTrace();
} catch (NoSuchMethodException x) {
x.printStackTrace();
} catch (InvocationTargetException x) {
x.printStackTrace();
err.format("%n%nCaught exception: %s%n", x.getCause());
}
}
}</source>



== Load class with Class.forName ==



<source lang="java">
/*
* Copyright (c) 1995 - 2008 Sun Microsystems, Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* - Neither the name of Sun Microsystems nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
public class ConstructorTrouble {
private ConstructorTrouble(int i) {
}
public static void main(String... args) {
try {
Class<?> c = Class.forName("ConstructorTrouble");
Object o = c.newInstance(); // InstantiationException
// production code should handle these exceptions more gracefully
} catch (ClassNotFoundException x) {
x.printStackTrace();
} catch (InstantiationException x) {
x.printStackTrace();
} catch (IllegalAccessException x) {
x.printStackTrace();
}
}
}</source>



== Modifier.PUBLIC | Modifier.PRIVATE | Modifier.PROTECTED ==



<source lang="java">
/*
* Copyright (c) 1995 - 2008 Sun Microsystems, Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* - Neither the name of Sun Microsystems nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
import static java.lang.System.out;
import java.lang.reflect.Constructor;
import java.lang.reflect.Modifier;
public class ConstructorAccess {
public static void main(String... args) {
try {
Class<?> c = Class.forName(args[0]);
Constructor[] allConstructors = c.getDeclaredConstructors();
for (Constructor ctor : allConstructors) {
int searchMod = modifierFromString(args[1]);
int mods = accessModifiers(ctor.getModifiers());
if (searchMod == mods) {
out.format("%s%n", ctor.toGenericString());
out.format(" [ synthetic=%-5b var_args=%-5b ]%n",
ctor.isSynthetic(), ctor.isVarArgs());
}
}
// production code should handle this exception more gracefully
} catch (ClassNotFoundException x) {
x.printStackTrace();
}
}
private static int accessModifiers(int m) {
return m & (Modifier.PUBLIC | Modifier.PRIVATE | Modifier.PROTECTED);
}
private static int modifierFromString(String s) {
if ("public".equals(s))
return Modifier.PUBLIC;
else if ("protected".equals(s))
return Modifier.PROTECTED;
else if ("private".equals(s))
return Modifier.PRIVATE;
else if ("package-private".equals(s))
return 0;
else
return -1;
}
}</source>



== Passing a parameter to the constructor and calling a method dynamically ==



<source lang="java">
public class Main {
public static void main(String args[]) throws Exception{
String name = "java.lang.String";
String methodName = "toLowerCase";
Class cl = Class.forName(name);
java.lang.reflect.Constructor constructor = cl.getConstructor(new Class[] { String.class });
Object invoker = constructor.newInstance(new Object[] { "AAA" });
Class arguments[] = new Class[] {};
java.lang.reflect.Method objMethod = cl.getMethod(methodName, arguments);
Object result = objMethod.invoke(invoker, (Object[]) arguments);
System.out.println(result);
}
}</source>

Java Tutorial/Reflection/Constructor - История изменений

в 17:44, 31 мая 2010

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