Class.forName() doesn't take dynamic class name

String name="";
String country="";
String className = name + "_" + language + "_" + country;
Class thisClass = Dynamicclassload.classLoad(className);
System.out.println(className);
Class class1 = Class.forName(className);
child = (ResourceBundle) class1.newInstance();
child.setParent( bundle );
bundle = child;
System.out.println("I am here");
As i am passing classname as variable it throws an exception class not found exception.but if we write class name as the parameter of class.forName().it works.i am implementing in j2me
why this happen? give me solution.

The following classpackage test;
public class TestLoad {
    String aString = "This is a Test";
    Integer anInteger = new Integer(42);
    public TestLoad() {
        System.out.println("aString = " + aString + ", anInteger = " + anInteger);
}works correctly when loaded and instantiated by this class:package test;
import java.util.logging.Logger;
public class ExecuteTest {
    public static final Logger log = Logger.getAnonymousLogger();
    public static void main(String[] args) {
        try {
            Class clazz = Class.forName("test.TestLoad");
            TestLoad test = (TestLoad) clazz.newInstance();
        } catch (Exception ex) {
            log.severe(ex.toString());
}and produces the string "aString = This is a Test, anInteger = 42"
I used the following version of Java on Windows 2000
java version "1.4.0"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.0-b92)
Java HotSpot(TM) Client VM (build 1.4.0-b92, mixed mode)

Similar Messages

War file doesn't take new classes

Not sure if this is right place to ask this question, but please help.
I had a war file deployed to weblogic 8 server, and I want to fix a problem quickly so I exploded the war file and put new classes files in /WEB-INF/classess directory. After I re-deploy this new war file, it still take the old version of classes file from somewhere I don't know.
Please help, I think this is short-cut to fix application but it turns to take even longer.

Not sure if you are stalled by a firewall or security in your web application or other mishap. Can you take a look at the relevant log at the server site? Look at the .log files at j2ee/home/log/. From *-web-access.log, you can determine if your url request indeed hit your server. From application-deployments/<youApp>/application.log, you would see the relevant exception.

Design patterns for Dynamic Class Loading

Hi,
I have to develop a program for uni that dynamically loads classes based on names in a text file. All the classes subclass an abstract class with a constructor that takes one argument. This means I can't use the Class.forName(className).newInstance() method of class loading. I have researched some design patterns I could use and have come up with the following 3:
Factory pattern; "Robocode" pattern (not it's real name, but Robocode uses it); and, the "one I made up myself" pattern.
The robocode pattern instantiates a class using the default no-argument constructor then immediately sets all properties that shoud have been provided in the constructor:
Object o = Class.forName(myClass).newInstance();
o.setProperty(property);Personally I think this is ugly and a cheap fix instead of doing it properly.
My own pattern finds the constructor that takes the arguments I need then calls it to create the object:
Class c = Class.forName(myClass);
Constructor cons = c.getConstructor(new Class[]{Class.forName("java.lang.String")});
Object o = cons.newInstance(new Object[]{"hello"});What's the best to use? Are there any other patterns I should consider?

My own pattern finds the constructor that takes the
arguments I need then calls it to create the object:
Class c = Class.forName(myClass);
Constructor cons = c.getConstructor(new
Class[]{Class.forName("java.lang.String")});
Object o = cons.newInstance(new Object[]{"hello"});
I have followed this basic 'pattern' several times though I would use
Constructor cons = c.getConstructor(new Class[]{String.class});
It works great.

Class.forName() debunked

This issue is about: Dynamic loading and Inheritance.
Debugging an odd ClassNotFoundException in a J2EE Application, I was involved investigating deeply Class.ForName(). This method - namely the version with only the class name as parameter - is used inside xsdbeans.jar, an optiopnal library, shipped with IBM WebSphere 5.x. Moving the jar from the EAR classloader to the server runtime classloader caused weird behavior on my app.
I try to simplify the core question:
Suppose class E extends B. Base class B declares an instance method, dynLoad(String name) that uses internally Class.forName(String name).
Say 'e' an instance of E. Invoking e.dynLoad("Foo"), Class.forName("Foo") should use the ClassLoader of current class. But which is the 'current class': E or B? Is it the class of current object (E) or the declaring superclass (B)?
My instinctive answer was: E. But my J2EE app was behaving as the current class was B. Indeed E and B may be defined by different classloaders, and this makes a big difference.
A rapid lookup at Sun's docs confirmed my first hypothesis:
http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Class.html#forName(java.lang.String)
> Returns the Class object associated with the class or interface with the given string name.
Invoking this method is equivalent to:
Class.forName(className, true, currentLoader)
where currentLoader denotes the defining class loader of the current class.
ok, this is a little misleading, but going on:
http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Class.html#forName(java.lang.String,%20boolean,%20java.lang.ClassLoader)
> For example, in an instance method the expression:
>
Class.forName("Foo")
is equivalent to:
Class.forName("Foo", true, this.getClass().getClassLoader())
Not equivocal. The current class is the class of current object, no matter (apparently) if the instance method is declared in a superclass.
Right? Wrong. Here a minimal counter-example:
//-- B.java
import java.net.*;
public class B {
    public void dynLoad(String name) throws Exception {
        System.out.println(getClass().getSuperclass()
            + " defining classloader is: "
            + getClass().getSuperclass().getClassLoader());
        System.out.println(getClass()
            + " defining classloader is: "
            + getClass().getClassLoader());
        System.out.println("\n1) Class.forName(\""+name+"\");");
        // Loading with 'currentLoader'
        Class.forName(name)
            .newInstance();
        System.out.println("\n2) Class.forName(\""+name
            +"\", true, this.getClass().getClassLoader());");
        // This should be equivalent (by Sun J2SE API spec)
        Class.forName(name, true, this.getClass().getClassLoader())
            .newInstance();
    public static void main(String[] args) {
        ClassLoader syscl = ClassLoader.getSystemClassLoader();
        if (!URLClassLoader.class.isInstance(syscl)) {
            System.err.println("Cannot continue the trick.");
            System.exit(1);
        URL[] urls = ((URLClassLoader)syscl).getURLs();
        // Yet Another ClassLoader
        URLClassLoader yacl = new URLClassLoader(urls) {
            // Force Parent-last delegation policy to assure
            // demanded classes are defined by _this_ classloader
            public Class loadClass(String name)
                throws ClassNotFoundException {
                Class c = findLoadedClass(name);
                if (c == null) {
                    try {
                        // Simulate no visibility to base class to assure
                        // it is _not_ defined by this classloader too
                        if (name.equalsIgnoreCase("B")) {
                            throw new ClassNotFoundException();
                        c = findClass(name);
                    } catch (ClassNotFoundException e) {
                        c = getParent().loadClass(name);
                return c;
        try {
            // Loading class E with a different classloader
            Class c = yacl.loadClass("E");
            c.getMethod("dynLoad", new Class[]{String.class})
                .invoke(c.newInstance(), new Object[]{"Foo"});
        } catch (Exception ex) {
            ex.printStackTrace();
            System.exit(1);
//-- E.java
public class E extends B {
//-- Foo.java
public class Foo {
public Foo() {
    System.out.println(getClass()
      + " defining classloader is: "
      + getClass().getClassLoader());
}Running above B.main() produce the following output on Sun JDK 1.3, 1.4.2, 1.5:
> class B defining classloader is: sun.misc.Launcher$AppClassLoader@3d200480
class E defining classloader is: B$1@3d2c0480
1) Class.forName("Foo");
class Foo defining classloader is: sun.misc.Launcher$AppClassLoader@3d200480
2) Class.forName("Foo", true, this.getClass().getClassLoader());
class Foo defining classloader is: B$1@3d2c0480
The evidence is that classloader used is not the same. in the case 1) it uses the classloader of superclass B. Hence the two form of Class.forName() invocation are not equivalent, as stated in Sun documentation.
Disclosure
The evidence is confirmed and explained looking at Sun's implementation of java.lang.Class.java and java.lang.ClassLoader.java: finally the Class.forName(String name) relies on sun.reflect.Reflection.getCallerClass(int) to find the famous 'current class' mentioned in the javadocs. This undocumented method returns the i-th caller class of current stack frames; each stack frame represents a method invocation coupled with its declaring class.
I wonder why in Sun docs this poorly explained issue was remaining immutable from 1.3 to date. Furthermore: which was the intended behavior? Another reason to the long said "Class.forName() is evil..." or am I missing something?
regards, Lorenzo

Of course, it comes down to the question: What is the current class?
Not something well defined. You are looking for this.getClass(), it's taking the class at compile time. If it went your way, woundn't that create an inconsistency in forName in static vs instance contexts?
Actually I think the static approach is more natural, because it means that forName behaves the way that resolving external references work. Your way would also go against the spirit of Java security policies which requires references down the classloader chain something to be treated with suspision.
The mechanism intended, I think, for these situations is the contextClassLoader property of Thread. When executing plugin type code the contextClassLoader should be set to the ClassLoader that loaded the plugin, and any references to resources or dynamic class loads from the plugin should be made using the contextClassLoader. This enables your shared library code to access classes and resources on behalf of the plugin code with access to classes and resources inside the plugin.
Thus, if you write library code or other container stuff likely to be called from a plugin you should probably always use:
Class cls = Thread.currentThread().getContextClassLoader().loadClass("foo");

How to create an object of our own class by using Class.forName()??

how to create an object of our own class by using Class.forName()??
plzz anser my qustion soon..

Class.forName does not create an object. It returns a reference to the Class object that describes the metadata for the class in question--what methods and fields it has, etc.
To create an object--regardless of whether it's your class or some other class--you could call newInstance on the Class object returned from Class.forName, BUT only if that class has a no-arg constructor that you want to call.
Class<MyClass> clazz = Class.forName("com.mycompany.MyClass");
MyClass mine = clazz.newInstance();If you want to use a constructor that takes parameters, you'll have to use java.lang.reflect.Constructor.
Google for java reflection tutorial for more details.
BUT reflection is often abused, and often employe when not needed. Why is it that you think you need this?

Use of Class.forName() in JDBC

Hi,
I know that in JDBC "Class.forName()" is used to load the JDBC driver classes.
Is this the only purpose of "Class.forName()" method specially in JDBC?

thanks much..
ok so. calling the Class.forName automatically
creates an instance of a driver and registers it with
the DriverManager.more or less
When we use the string / string buffer class we don�t
need to explicitly load the classes exist in
�java.Lang� package.they get loaded - as do all classes - when your code first tries to use them.
But to get the JDBC connection, we need to insert the
code
�Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");�..
please clear my confusion.it's really because the JDBC driver might not be known at compile-time. Class.forName allows us to load classes at runtime we didn't know about at compile-time. you could just as easily load java.lang.String using the above method, but since the method takes a string, the class will be loaded already! you could also just as easily do
import sun.jdbc.odbc.JdbcOdbcDriver;
new JdbcOdbcDriver();that would also load the class. but that then couples your code to that particular driver. generally, in real applications, the driver classname would come from a config file, rather than hard-coded in the application. Class.forName() gives us that flexibility

Difference between DriverManager.registerDriver and Class.forName?

Hi all,
I've noticed that the Oracle JDBC driver specifically asks to use DriverManager.registerDriver instead of Class.forName. What is the difference btw those 2 methods in loading and registering the driver?
Thanks.

I am trying to understand the jdbc, odbc drivers better.
Does the class my.sql.Driver refer to a driver for MySql or is it a driver itself?
with the lines one and two commented out, the code works fine. but with lines one and three commented out and the dbDriver being as specified in line two; no connection is made to the database. Can anyone explain this? and when i do Class.forName(dbDriver), is there a class by that name?
//String dbDriver = "sun.jdbc.odbc.JdbcOdbcDriver"; //one
//String dbDriver = "my.sql.Driver"; //two
String dbDriver = "MySql ODBC 3.51 Driver"; //three
String dbSource = "jdbc:odbc:mydb";
try {
     Class.forName(dbDriver);
     conn = DriverManager.getConnection(dbSource);
     statement = conn.createStatement();
} catch(Exception exception) {
     System.out.println(exception.getMessage()+" from the "+exception.toString());
     System.exit(1);

Class.ForName, is it possible?

if a class has not been compiled, in other words, the class is only a name in .java file, could we use Class.ForName to get its information?
if not, is there any other idea to get the class info from .java file? -- i mean, not open the jave file as buffer to read what text is on it - is there a method similar to Class.ForName in the case?
thx

if a class has not been compiled, in other words, the
class is only a name in .java file, could we use
Class.ForName to get its information?No. Class.forName only works on compiled classes within the classpath.
if not, is there any other idea to get the class info
from .java file? -- i mean, not open the jave file as
buffer to read what text is on it - is there a method
similar to Class.ForName in the case?If your question is how to get class info by not compiling it one,
and not reading the .java source file two, the answer again is no.
Simply because the demand is unreasonable.
If your question is Is there any helper class to read .java
source file and give back the class info, the answer is yes. And
the java compiler is exactly what this helper class is. Do you know
javac is actually a java program, and in turn it is a java
class?
Let me know if this is what you are looking for and need more info
on how to compile a java file inside another class.
--lichu

(Class ? extends Set String ) Class.forName("example.SetImpl").asSubclass

Is there a way to do the following without an Unchecked cast?
Class<? extends Set<String>> clazz;
clazz = (Class<? extends Set<String>>) Class.forName("example.SetImpl").asSubclass(Set.class);
Set<String> mySet = clazz.newInstance();
cheers,
reto

No. The last line will always generate that warning making the second line pointless. There is no way to create a new instance of a generic class because there is (for most intents and purposes) no such thing as a generic class at runtime.

Bindable Dynamic Class

Hi,
I'm trying to write a class to load an XML config file and
make the settings accessible as properties of the config class.
Now using a dynamic class i can make the properties
accessible, but i would also like to make them bindable.
Does anyone know how to go about this?
Many thanks
Matt

Try making the actual instance of the dynamic object
bindable, then you can bind to its properties.

-Xbootclasspath, -classpath & Class.forName

I am running into a problem as follows.
Our product depends on using the most recent versions of Xerces & Xalan so we prepend the path to ours using -Xbootclasspath. Xerces provides the ability to specify a custom document factory to create custom implementations of the DOM classes.
I have a class in the classes loaded with -classpath that implements this factory to produce some custom implementations.
I specify the fully qualified classname to the DOMParser. However, when it goes to load my custom class using Class.forName, it cannot find my class.
I have experienced the exact reverse of this as well. I have classes in the -classpath that do a Class.forName for classes in -Xbootclasspath and it fails to find those classes.
Is this a bug? Is there any way around it? We have to have the most recent copies of Xerces and Xalan, so we are stuck using -Xbootclasspath since it is the only way to override the bootstrap classes. However, we also have a class which MUST be loaded in -classpath because it uses a native library and there is currently a bug with loading JNI libraries from classes specified in -Xbootclasspath.
Any suggestions/comments?
Thanks,
Scott

Aren't you trying to solve the second problem here? The first problem was that you couldn't see the current version of Xerces and Xalan when you ran your class, because there was something else in the boot classpath that interfered with them. Evidently your solution to that problem isn't working (and I don't know how to make it work either). What kind of environment are you running under that makes you have an XML parser in your boot classpath? Surely you must already have considered just replacing that parser by Xerces?

Dynamic class loading problem using unknown JAR archive and directory names

I read the following article, which enlightened me a lot:
Ted Neward: Understanding Class.forName().
However, it took me some while to understand that my problem is the other way around:
I know the name of the class, I know the name of the method,
but my program/JVM does not know where to load the classes from.
Shortly, my problem is that the server engine that I am writing
uses two different versions of the same library.
So I am trying out the following solution:
My program is named TestClassPathMain.java
Assume the two libraries are named JAR1.jar and JAR2.jar
and the class/instance method that should
be exposed to TestClassPathMain.java by them is named
TestClass1.testMethod().
As long as I was depending on just one library,
I put JAR1.jar in the classpath before starting java,
and I was happy for a while.
At the moment I got the need to use another version of
TestClass1.testMethod() packaged in JAR2.jar,
a call would always access JAR1.jar's
TestClass1.testMethod().
I then decided to remove JAR1.jar from the classpath,
and programmatically define two separate ClassLoaders, one for use
with JAR1.jar and the other for use with JAR2.jar.
However, the problem is only partly solved.
Please refer to the enclosed code for details.
(The code in the JAR1.jar/JAR2.jar is extremely simple,
it just tells (by hardcoding) the name of the jar it is packaged in
and instantiates another class packaged in the same jar using
the "new" operator and calls a method on it. I don't enclose it.)
The TestClassPathMain.java/UC1.java/UC2.java code suite was
successfully compiled with an arbitrary of JAR1 or JAR2 in the classpath,
however removed from the classpath at runtime.
(I know that this could have been done (more elegantly...?) by producing an Interface,
but I think the main problem principle is still untouched by this potential lack of elegancy(?))
1) This problem should not be unknown to you experts out there,
how is it generally and/or most elegantly solved?
The "*** UC2: Variant 2" is the solution I would like best, had it only worked.
2) And why arent "*** UC2: Variant 2" and
"*** static UC2: Variant 2" working,
while "*** Main: Variant 2" is?
3) And a mal-apropos:
Why can't I catch the NoClassDefFoundError?
The output:
*** Main: Variant 1 JAR 1 ***:
Entering TestClass1.testMethod() packaged in JAR1.jar
About to instantiate TestClass2 with the new operator
About to call TestClass2.testMethod()
Entering TestClass2.testMethod() packaged in JAR1.jar
*** Main: Variant 1 JAR 2 ***:
Entering TestClass1.testMethod() packaged in JAR2.jar
About to instantiate TestClass2 with the new operator
About to call TestClass2.testMethod()
Entering TestClass2.testMethod() packaged in JAR2.jar
*** Main: Variant 2 JAR 1 ***:
Entering TestClass1.testMethod() packaged in JAR1.jar
About to instantiate TestClass2 with the new operator
About to call TestClass2.testMethod()
Entering TestClass2.testMethod() packaged in JAR1.jar
*** Main: Variant 2 JAR 2 ***:
Entering TestClass1.testMethod() packaged in JAR2.jar
About to instantiate TestClass2 with the new operator
About to call TestClass2.testMethod()
Entering TestClass2.testMethod() packaged in JAR2.jar
*** UC1: Variant 1 JAR 1 ***:
Entering TestClass1.testMethod() packaged in JAR1.jar
About to instantiate TestClass2 with the new operator
About to call TestClass2.testMethod()
Entering TestClass2.testMethod() packaged in JAR1.jar
*** UC1: Variant 1 JAR 2 ***:
Entering TestClass1.testMethod() packaged in JAR2.jar
About to instantiate TestClass2 with the new operator
About to call TestClass2.testMethod()
Entering TestClass2.testMethod() packaged in JAR2.jar
*** static UC2: Variant 2 JAR 1 ***:
Exception in thread "main" java.lang.NoClassDefFoundError: TestClass1
        at UC2.runFromJarVariant2_static(UC2.java:56)
        at TestClassPathMain.main(TestClassPathMain.java:52)
TestClassPathMain.java
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
public class TestClassPathMain {
    public static void main(final String args[]) throws MalformedURLException, ClassNotFoundException, InstantiationException, SecurityException, NoSuchMethodException, IllegalArgumentException, IllegalAccessException, InvocationTargetException {
            // Commented out because I cannot catch the NoClassDefFoundError.
            // Why?
            try {
                final TestClass1 testClass1 = new TestClass1();
                System.out.println(
                    "\nThe class TestClass1 is of some unexplicable reason available." +
                    "\nFor the purpose of the test, it shouldn't have been!" +
                    "\nExiting");
                System.exit(1);
            } catch (NoClassDefFoundError e) {
                System.out.println("\nPositively confirmed that the class TestClass1 is not available:\n" + e);
                System.out.println("\n\nREADY FOR THE TEST: ...");
            // Works fine
            System.out.println("\n*** Main: Variant 1 JAR 1 ***:");
            runFromJarVariant1("file:/W:/java/eclipse/workspaces/simped_test/CP1/JAR1.jar");
            System.out.println("\n*** Main: Variant 1 JAR 2 ***:");
            runFromJarVariant1("file:/W:/java/eclipse/workspaces/simped_test/CP2/JAR2.jar");
            // Works fine
            System.out.println("\n*** Main: Variant 2 JAR 1 ***:");
            runFromJarVariant1("file:/W:/java/eclipse/workspaces/simped_test/CP1/JAR1.jar");
            System.out.println("\n*** Main: Variant 2 JAR 2 ***:");
            runFromJarVariant1("file:/W:/java/eclipse/workspaces/simped_test/CP2/JAR2.jar");
            // Works fine
            final UC1 uc1 = new UC1();
            System.out.println("\n*** UC1: Variant 1 JAR 1 ***:");
            uc1.runFromJarVariant1("file:/W:/java/eclipse/workspaces/simped_test/CP1/JAR1.jar");
            System.out.println("\n*** UC1: Variant 1 JAR 2 ***:");
            uc1.runFromJarVariant1("file:/W:/java/eclipse/workspaces/simped_test/CP2/JAR2.jar");
            // Crashes
            System.out.println("\n*** static UC2: Variant 2 JAR 1 ***:");
            UC2.runFromJarVariant2_static("file:/W:/java/eclipse/workspaces/simped_test/CP1/JAR1.jar");
            System.out.println("\n*** static UC2: Variant 2 JAR 2 ***:");
            UC2.runFromJarVariant2_static("file:/W:/java/eclipse/workspaces/simped_test/CP2/JAR2.jar");
            // Crashes
            final UC2 uc2 = new UC2();
            System.out.println("\n*** UC2: Variant 2 JAR 1 ***:");
            uc2.runFromJarVariant2("file:/W:/java/eclipse/workspaces/simped_test/CP1/JAR1.jar");
            System.out.println("\n*** UC2: Variant 2 JAR 2 ***:");
            uc2.runFromJarVariant2("file:/W:/java/eclipse/workspaces/simped_test/CP2/JAR2.jar");
    private static void runFromJarVariant1(final String jarFileURL)
        throws MalformedURLException,
               ClassNotFoundException,
               InstantiationException,
               IllegalArgumentException,
               IllegalAccessException,
               InvocationTargetException,
               SecurityException,
               NoSuchMethodException {
        final URL url = new URL(jarFileURL);
        final URLClassLoader cl =
            new URLClassLoader(new URL[]{url},
                               Thread.currentThread().getContextClassLoader());
        final Class clazz = cl.loadClass("TestClass1");
        final Object testClass1 = clazz.newInstance();
        final Method testMethod1 = clazz.getMethod("testMethod", null);
        testMethod1.invoke(testClass1, null);
    private static void runFromJarVariant2(final String jarFileURL)
        throws MalformedURLException,
               ClassNotFoundException,
               InstantiationException,
               IllegalArgumentException,
               IllegalAccessException,
               InvocationTargetException,
               SecurityException,
               NoSuchMethodException {
        final URL url = new URL(jarFileURL);
        final URLClassLoader cl =
            new URLClassLoader(new URL[]{url},
                               Thread.currentThread().getContextClassLoader());
        final Class clazz = cl.loadClass("TestClass1");
        final TestClass1 testClass1 = new TestClass1();
        testClass1.testMethod();
UC1.java
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
public class UC1 {
    public void runFromJarVariant1(final String jarFileURL)
        throws MalformedURLException,
               ClassNotFoundException,
               InstantiationException,
               IllegalArgumentException,
               IllegalAccessException,
               InvocationTargetException,
               SecurityException,
               NoSuchMethodException {
        final URL url = new URL(jarFileURL);
        final URLClassLoader cl =
            new URLClassLoader(new URL[]{url},
                               Thread.currentThread().getContextClassLoader());
        final Class clazz = cl.loadClass("TestClass1");
        final Object testClass1 = clazz.newInstance();
        final Method testMethod1 = clazz.getMethod("testMethod", null);
        testMethod1.invoke(testClass1, null);
UC2.java
import java.lang.reflect.InvocationTargetException;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
public class UC2 {
    public void runFromJarVariant2(final String jarFileURL)
    throws MalformedURLException,
           ClassNotFoundException,
           InstantiationException,
           IllegalArgumentException,
           IllegalAccessException,
           InvocationTargetException,
           SecurityException,
           NoSuchMethodException {
        final URL url = new URL(jarFileURL);
        final URLClassLoader cl =
            new URLClassLoader(new URL[]{url},
                               Thread.currentThread().getContextClassLoader());
        final Class clazz = cl.loadClass("TestClass1");
        final TestClass1 testClass1 = new TestClass1();
        testClass1.testMethod();
     * Identic to the "runFromJarVariant2" method,
     * except that it is static
    public static void runFromJarVariant2_static(final String jarFileURL)
    throws MalformedURLException,
           ClassNotFoundException,
           InstantiationException,
           IllegalArgumentException,
           IllegalAccessException,
           InvocationTargetException,
           SecurityException,
           NoSuchMethodException {
        final URL url = new URL(jarFileURL);
        final URLClassLoader cl =
            new URLClassLoader(new URL[]{url},
                               Thread.currentThread().getContextClassLoader());
        final Class clazz = cl.loadClass("TestClass1");
        final TestClass1 testClass1 = new TestClass1();
        testClass1.testMethod();
}

2. i need to load the class to the same JVM (i.e. to
the same environment) of the current running
aplication, so that when the loaded class is run, it
would be able to invoke methods on it!!!
ClassLoader(s) do this. Try the URLClassLoader.
(I was talking about relatively esoteric "security"
issues when I mentioned the stuff about Class objects
"scope".) You might use the URLClassLoader kind of
like this.
Pseudo-code follows:
// setup the class loader
URL[] urls = new URL[1];
urls[0] = new URL("/path/to/dynamic/classes");
URLClassLoader ucl = new URLClassLoader(urls);
// load a class & use make an object with the default constructor
Object tmp = ucl.loadClass("dynamic.class.name").newInstance();
// Cast the object to a know interface so that you can use it.
// This may be used to further determine which interface to cast
// the class to. Or it may simply be the interface to which all
// dynamic classes have to conform in your program.
InterfaceImplementedByDynamicClass loadedObj =
    (InterfaceImplementedByDynamicClass)tmp;It's really not as hard as it sounds, just write a little test of
this and you will see how it works.

Class.forName() with dynamic String

I'm trying to create objects of a class whose name depends on a runtime database lookup. So my code looks like this:
package com.mycompany.ourproduct.ourpackage;
String className = rs.getString(1);
Class c = Class.forName(className);
When I run the program, I get a ClassNotFoundException. But everything runs fine if I replace the code above with this:
package com.mycompany.ourproduct.ourpackage;
// String className = rs.getString(1);
String className = "com.mycompany.ourproduct.ourpackage.oursubpackage.MyClass"
Class c = Class.forName(className);
The problem seems to be in the dynamic linking. Although the class I'm trying to load is in a different package, it is a public class (and I can load it with a static string). Neither does moving it to the same package fix the problem.
I've noticed that if I supply a mis-named class with a static string, the exception reads:
java.lang.ClassNotFoundException: com.mycompany.ourproduct.misspelledpackage.SomeClass
but the same exception prints as follows when the string comes from the database:
java.lang.ClassNotFoundException: com/mycompany/ourproduct/misspelledpackage/SomeClass
I thought the difference was one of compile-time linking and run-time linking, but oddly enough, I still get the dots for misspelled classes that I (1) supply on the command line, (2) read from a file, or (3) concatenate from command line arguments plus info from a file. It's just when I pull the class name from the database that I get the slashes. Does anyone know what's going on?
Here's what I get from java -version:
java version "1.2.2"
Solaris VM (build Solaris_JDK_1.2.2_05a, native threads, sunwjit)
Any help would be greatly appreicated!

Hmm. Weird. Have you looked at the String you're getting back from the database? Does it have slashes or dots? (Should be dots.) Have you made sure any leading/trailing spaces have been trimmed? Try doing classname.equals("com.mycompany... etc.") to see if it really is the same string as the constant that does work.
If it turns out the String is correct, and the only difference is whether that String came from a databaes or a literal, then I don't know what's going on. The first step, though, is to verify whether that's really the case, or if you're not getting the String you think you are.

Dynamic class loading from String name

Hello all,
I have a question for dynamic class loading:
If I have a String variable that represents a class name, how can i use it to make dynamically an object of the class tha the string variable represents?
For example i have a string like this
String classname="String";
Using this i want to make a new String object .
Can anyone tell me how can i do this(example plz)?

I have worked out the code and this works fine:
import java.lang.*;
class dynamictestname{
     public dynamictestname() {
    public static Class test(String objname){
         try{
         Class theClass = Class.forName(objname);
             return theClass;
        } catch (ClassNotFoundException e)
            throw new NoClassDefFoundError (e.getMessage());
     public static void main (String [] args){
          String classname="java.lang.String";
          Class thisClass=dynamictestname.test(classname);
          try{
          Object instance = thisClass.newInstance();
          }catch(InstantiationException e){
          }catch(IllegalAccessException ie){
}The new problem i 've faced is that i can't instatiate a new object by the class i have created.I saw some examples with use of the java.lang.reflect but this class i used with user created classes which have methods that the user wants to run dynamically.
I just want to make an object from the class and give it a value.
For example if the object i have created with the
Object instance = thisClass.newInstance();is an object of java.lang.String class
how can i do something like this below dynamically from instance object :
String x="TEST ";
Thanks for the help..

AS3 - dynamic class names with *new* operator

I'm using AcrtionScript 3 and Adobe Flash 9 Public Alpha.
I have 50 movie clips in the Library that use Linkage to set
the Class name to: Img1, Img2, Img3, ..., Img50.
I have a parent class named RandImg. I want the constructor
for RandImg to randomly select one of the 50 movie clips from the
Library and display it. I could get this working by generating a
random number, and then writing a really huge switch statement to
associate each possible random number with its respective Library
Movie Clip Class name, but I would much rather do this with a
dynamic/variable class name based on the random number, such as:
var nImgChoice:Number = Math.floor( Math.random( ) * 50 ) +
1;
var mcImg:MovieClip = new [ "Img"+String(nImgChoice) ] ( );
addChild( mcImg );
Note that this used to be possible in AS 2 by doing the
following:
this.attachMovie( "Img"+String(nImgChoice) , "mcImg",
this.getNextHighestDepth());
Suggestions?
Thanks,
~JC

import flash.display.DisplayObject;
import flash.display.Sprite;
import flash.utils.getDefinitionByName;
var nImgChoice:Number = Math.floor( Math.random( ) * 50 ) +
1;
var ClassReference:Class =
getDefinitionByName("Img"+String(nImgChoice) ) as
Class;
var instance:Object = new ClassReference();
addChild(DisplayObject(instance));

Class.forName() doesn't take dynamic class name

Similar Messages

Maybe you are looking for