I'm getting the cannot find symbol error from my code. Does anyone know what can cause this problem?
The code is:
// Register JDBC driver
Class.forName("net.sourceforge.jtds.jdbc.Driver");
and the error output is:
blah.java:314: cannot find symbol
symbol ...
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My code is as follows
package com.foo;
public class TestComposition {
public static void main(String[] args) {
try {
...
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before asking, please understand that my english is not good.
I'm using Class.forName(...) class in a servlet programming. when I access the servlet, I get a row of detailed controller information from ... |
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Class.forName() doesn't instantiate an object (at least not an object of the class you are calling it for, it might instantiate a Class object). All it does is preload the class for the given name, allowing objects to be instantiated from it. Class.forName().newInstance() would actually create an instance. This is useful in situations when the class name to be instantiated cannot ... |
Originally posted by Kartik Patel: Doen't the contextclassloader and class's classLoader are same? No, certainly not. The current class's ClassLoader is whatever loaded that class and is fixed. The thread context ClassLoader is under your control; you can set it. If you haven't set it yourself, it defaults to the thread context ClassLoader of the thread that started the ... |
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Well, think of how the Java Plug-in, which lets Applets run inside of Web browsers, would work. It sees something like this in the HTML: and it know that it should run the Applet class com.foo.MyApplet. How does it do this? Using Class.forName()! It parses the applet tag, gets the String "com.foo.MyApplet", and then says something like ... |
Class.forName(...) loads the class that you specify using the current ClassLoader. What do you want to know more, what the JVM internally does when you call this? You can have a look at the source code. In your JDK folder, you should have a file called src.zip. In this file, lookup the source code for class java.lang.Class. If you look at ... |
Okay, here's what's already being done: Object service = Class.forName(passedServiceName).newInstance(); //use the service's info DS ds = new DS(); ds.setValue = ( (OtherService) service) ).getValue(); This is causing an incredible amount of coding: if (passedServiceName.equals("Service1") { ds.setValue = ((Service1) service).getValue(); } else if (passedServiceName.equals("Service2") { ds.setValue = ((Service2) service).getValue(); } ... etc. I want to have one set of code that ... |
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One example I can think of is the old days of JDBC. You can still see examples of this workaround in current code through the wonders of "cut and paste". As EFH says, Class.forName() gets a reference to a Class, Class.forName().newInstance() tries to use the no-arg constructor for the Class to return a new instance. No surprises so far. Another common ... |
Hi All, I am new to java.we are using class.forName() for loading classes.i have one doubt in this topic, this function we are using in jdbc for load the class and getting connection here we are just loading the class what's happening on loading time.if we need to do anything on loading time we should implement static block, are they using ... |
It's particularly useful to dynamically create instances from their fully-qualified path. For example : package output; public interface OutputObject { public void write(String message); } package output; public class FileOutputObject implements OutputObject { public void write(String message) { // Write the message to a file } } package output; public class ConsoleOutputObject implements OutputObject { public void write(String message) { // ... |
I'm trying to use Class.forName to give me one of several named classes. I have a parent Abstract class that has a common abstract method that each child implements. When I try: ParentClass myClass = Class.forName("childClassString"); myClass.implementedAbstractMethod(data); The compiler gives me a "type mismatch" error. When I change ParentClass to Class then I get a "method not defined" error. I've tried ... |
It seems you are touching two different issues here. The reason JDBC drivers are usually loaded into the virtual machine with Class.forName() is that it is a more flexible design choice. You can read the names of drivers from a configuration file at runtime, rather than writing them all into the program at compile time. The reason you must load them ... |
Offhand, example 1 does seem rather silly, and most likely there is no good reason for it, IMO. One effect of the statement though is that it does force the class to be loaded at that point if it hasn't already - which included executing static initializers and initialization expressions for static variables. Perhaps one of these would be particularly slow ... |
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - ... |
Maybe I didn't explain my question clearly.In fact I want know the following: 1 how to use the method of class.forName() that it works in findng a existing class without throwing the exception. 2 how to use the classloader 3 Moreover, how can i know the sequence that the classloader load in the classes. |
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Hi, welcome to the ranch! Sometimes we know the name of a class at runtime but not at compile time. We can use Class.forName() to get the Class or an instance. Think of a plugin system, maybe something that adds new commands to an editor. In the configuration we might say "when the user enters this string, run this class". At ... |
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--> I have read that Class.forName() is to load the class dynamically. --> And one of the places it is used is to load the Driver in jdbc. --> for e.g. --> Class.forName("com.mysql.jdbc.Driver"); Normally what you will do is have the driver in a properties file and then call Class.forName(myDriverProperty); That way by changing the value in the properties file you ... |
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Class.forName() returns a Class object. (There is a class named Class!) This is part of the Reflection API which is a very powerful feature of Java. The above posts describe just a few examples of how the Reflection API can be used. I suggest that you google for "reflection api java" or something similar. There are plenty of examples and tutorials ... |
You write Class.forName("drivername") because you want to load the drivers class so that it will register as a driver to the DriverManager. You have just altered the syntax a bit by importing the driver class and you use Driver.class.newInstance() to load the driver into memory so that it will be possible to use the DriverManager to create the connection. In most ... |
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Class.forName() is a method of the class, Class that takes a String which is the name of a class and returns an object of type Class. This is usually used to dynamically instantiate an object as in the following example. This kind of advanced instantiation in place of using the new operator can be used when the class to be instantiated ... |
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//com.me.A.java package com.me; public class A { public A() {} ... } //com.you.B.java public class B { public B() { Class cls = A.class; //got java.lang.NoClassDefFoundError exception try { Class cls = Class.forName("com.me.A"); } catch (Exception e) { // got Exception } Class clzz = new A().getClass(); // works. ... } } |
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You can use it to dynamically load classes, i.e. classes that your program needs to use, but of which you don't know the class name beforehand (at compile time). It's useful for plugin systems, for example. The JDBC driver is a good example: your program should not need to know at compile time which JDBC driver has to be used; it ... |
Hello guys, I have a problem with Class.forName() In a method of a class I have a string variable which stores a class name like this.. void myMethod() { String str1 = "com.matrix.heman"; } In the above myMethod I need to create an object of the class "com.matrix.heman" and invoke the main method of it by passing some arguments. I did ... |
i have below files(both .java and .class files) in my code. com.cvs.tpms.prm.ProductionManager com.cvs.tpms.jms.gui.AgentApplication com.cvs.tpms.gui.DeviceManager com.cvs.tpms.gui.ProcessManager com.cvs.bit.cache.ui.CacheManager in code, i am using like this final Class applicationClass = Class.forName(string .asString()); string.asString() gives the path of the class i.e com.cvs.tpms.prm.ProductionManager. I am dynamically loading the classes by using class.forName() method. I am able to load all the classes except CacheManger.when i am trying ... |
hi friends, i am confused in using Class.forName() method. it simply load the specified class to a class object. and i got that. Class c = Class.forName("Class4Name"); Object o = c.newInstance(); here class os loaded in to c and we can use 'c' to make object of that class. but in database driver loading code i found Class.forName("oracle.jdbc.driver.OracleDriver"); con=DriverManager.etConnection( "jdbc:oracle:thin:@machine_name:1521:database_name ... |
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Class.forName has nothing to do with JDBC. It's just a way to load a class--any class. DriverManager.registerDriver is how you tell the JDBC DriverManager that there's a driver available to access some DB. Of course, the above could have been gleaned by reading the docs for those classes. Now, it so happens that properly implemented JDBC drivers will have a static ... |
A jar file contains the class file for the string received above and I have this jar file in the manifest of my executable jar. I get a class not found exception when I run my executable jar Can some body give pointers..what could possibly be the issue. *************************** The jar file is in my classpath Message was edited by: chabhi ... |
Determines if the specified Object is assignment-compatible with the object represented by this Class. This method is the dynamic equivalent of the Java language instanceof operator. The method returns true if the specified Object argument is non-null and can be cast to the reference type represented by this Class object without raising a ClassCastException. It returns false otherwise. |
Hi, I'm trying to convert string having value which represents class name into a class using Class.forName but it is not working when I tried to catch exception it and print message it is giving me string's value which I have passed as a message and nothing else pleasehelp me. eg. String str=null; try { str = "some_classname_which is passed"; Class ... |
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Hello, I am receiving a ClassNotFoundException on a class in my application during a Class.forName call and I have no idea why. The class is present at the correct path, all words are spelled correctly, and all case-sensitivity is correct. If I even try to instantiate the object which the class represents in my code, it works fine. I actually realized ... |
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Class.forName works with a parameter obtained possibly at runtime. You can put a class name into the configuration and load it dynamically. If the given class has an (accessible) no-arg constructor, an instance can be obtained with newInstance(). If you know that the class implements a given interface (known at compile time), or it extends a known base type, you can ... |
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A jar file contains the class file for the string received above and I have this jar file in the manifest of my executable jar. I get a class not found exception when I run my executable jar Can some body give pointers..what could possibly be the issue. The jar file is in my classpath run script ****************************** #!/bin/csh java -jar ... |
Hi everyone, I have come across a problem and wanted to know if anyone has faced a similar problem on RHEL 64 linux JDK1.5. java.lang.ClassNotFoundException: com.company.abc.runtime.session.impl.FTlrtAsyncRServiceProviderImpl at java.net.URLClassLoader$1.run(URLClassLoader.java:200) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:188) at java.lang.ClassLoader.loadClass(ClassLoader.java:306) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:268) at java.lang.ClassLoader.loadClass(ClassLoader.java:251) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:164) The peculiarity is there is another class com.company.abc.runtime.session.impl.FTReadServiceProviderImpl in the same package com.company.abc.runtime.session.impl which gets ... |
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Object does not have a Title member, that is why you get the error. If all of your classes implemented an interface with a method to get the title you could cast the object returned and get the title that way. I believe you could also get the member using other reflection methods such as Class.getField() and Field.toString(). Message was edited ... |
What is the difference between these two statements a.b.c.ABC abc = new a.b.c.ABC(); and a.b.c.ABC abc = Class.forName('a.b.c.ABC).getInstance(); which one is better approach. and if there is no difference then why two approaches. and if Class.forName() returns the class object of a particular class, then why can't can't we simply use, ClassName.class, eg. Class c = a.b.c.ABC.class; My main confusion is: ... |
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