I am referencing PlayerUtil.getMovementSpeed(player); in my Speed class, and in my PlayerUtil class, I have the method defined as:
public static double getMovementSpeed(Player player) {
//my code here
}
But whenever the getMovementSpeed method is referenced in my other classes, it throws this error:
java.lang.NoSuchMethodError: net.Swedz.util.PlayerUtil.getMovementSpeed(Lorg/bukkit/entity/Player;)D
I thought it may be that Eclipse was exporting incorrectly, but I rebooted it and tried again with no avail.
EDIT: I did try decompiling the exported jar, and the public static double getMovementSpeed(Player player) method does exist in the exported jar.
EDIT: My friend is also having a similar issue, and is using IntelliJ, so Eclipse is not the issue.
EDIT: Class definition for PlayerUtil:
package net.Swedz.util;
public class PlayerUtil implements Listener {
//getMovementSpeed is defined in here
}
Class definition for Speed:
package net.Swedz.hack.detect.move;
public class Speed implements Hack, Listener {
//my detection methods and method containing PlayerUtil.getMovementSpeed(player);
}
SOLUTION: I found on my own that I had classes conflicting between two plugins on my server. I had one jar with net.Swedz.util.PlayerUtil and another with net.Swedz.util.PlayerUtil both with different contents. I added my project name in all lower case after the net.Swedz and it seems to have fixed it!
Thanks!
This is a very simple to troubleshoot.
you have used that method and you were able to compile that class which uses this method.
so that means at compile time it reefers the class PlayerUtil which has this method.
But runtime class loader has loaded the class PlayerUtil which doesn't contain this method.
now what you have to do is just find out where that class has been loaded from (at run time)
if you can recreate the problem while it is running using eclipse/IDEA follow these steps.
(if it runs in in application server or standalone application, then start the application server or application with debug enabled.and you can do remote debug from your IDE).
put a break-point where exception was thrown (where you call this method).
start to debug , it will hit the break-point.
then evaluate this expression PlayerUtil.class.getResource("PlayerUtil.class")
4.you can find the path where the class was loaded from.
now you have two options , decompile the class and check whether that method is these (same return type, same name , same args).
or in debug , you can evaluate PlayerUtil.class.getDeclaredMethods() to find out.
So you can solve the problem by rectifying the class path entries if it was loaded from a wrong place.
chinmay#chinmay-desktop:~$ javac hello.java
hello.java:3: class readnumbers is public, should be declared in a
file named readnumbers.java public class readnumbers
^ 1 error
When I compile any program I get the same error. And now I'm tired of this. Help me out.
Your class name is readnumbers and you have saved it as hello.java
In Java, all public classes (in your case readnumbers) must be contained in a file name same as the class name
Solution - rename file to readnumbers.java OR change the class name to hello
Please note that -
As per Java naming conventions, Java class should start with Capital letter and should follow Camel casing incase of multiple words, for example
Hello
ReadNumbers
What part of the error message do you not understand? It clearly tells you that your class and your java file must have the same name. So either rename your class to hello, or your file to readnumbers.java.
The error says it all.
Your class readnumbers should be declared in a file named
readnumbers.java.
Basically to run a java code you need to write the public class in a file with the same name of the class. For example if your class is A then save it in A.java file.
Java class and filename should be the same. That's why you get this error.
public class readnumbers in file readnumbers.java
I am a beginner in Java. Could anyone please help me understand the following concept?
What I have done here is I tried to create a class as Sample, which I mentioned below, where I am printing You are in Main Method
class Sample
{
public static void main(String args[]) {
System.out.println("You are in Main Method");
}
}
and saved this java file as Student.java.
I didn't get any error in Eclipse.
Now, I had specified a public in front of this class as public class Sample and I am getting an error.
Could anyone please clarify for me with the right answer, as I am finding this to be difficult to understand?
In Java all classes with scope public must be save in file which name is exactly the same like name of this class. So if you have class named Sample it has to be saved in file named Sample.java. If class is named Student then file should be named Student.java
One of reason for this is that packages named and class names can be easly mapped to real system paths.
Ensure that the class name is equal to the file name appended with ".java". So if you name your class Sample then the file should be named Sample.java. This is why you're getting the error because your class name is different to what you have named the file.
For future references, when you're getting a compiler error/run time error, whatever, please ensure that you list the error here. It makes it a lot easier to deal with the problem, and the chances that you will get an answer that actually solves your problem increases.
All public class must be saved with the same name.
So if you have class named Sample it has to be saved in file named Sample.java
If you use a package, you have to save file in this folder.
Example com.example, you have to save Sample.java in a folder root/com/example.
package com.example;
public class Sample{
public static void main(String[] args){
// put here your code
}
}
Public classes must have their own compilation units (i.e. .java files which must match the class name) and are compiled into ClassName.class files.
This way the JDK knows where it should generate the output .class files and the JVM know where to load the .class files from.
An exception to this would be inner/nested classes which do not require a separate file and that get their byte code generated into files like OuterClassName#InnerClassName.class. Inner classes are stored in the same .java file as the outer class that defines them.
Note:ClassName, OuterClassName and InnerClassName are the names of the classes defined by you.
first u read visibility of modifies i think u r well understanding ur problem
Access Modifiers
Same Class Same Package Subclass Other packages
public Y Y Y Y
protected Y Y Y N
no access modifier Y Y N N
private Y N N N
I get this error:
Exception in thread "http-server" java.lang.NoClassDefFoundError: org/w3c/jigmonitor/ReplyServer
but I don't undestand why. Could someone explain why does this happen?
This is the class that causes the problem:
public class ReplyServer implements Serializable
{
public ReplyServer()
{
super();
}
}
It looks like the class you're defining isn't being found by something that's trying to load it. In my experience this is caused by one of three problems:
Your package declaration for the class is not correct. In this case something on the http-sever thread is expecting your class to be declared in the package org.w3c.jigmonitor.
Your source file is not located in the correct directory. In this case, your source file should be located in a directory structure like "org/w3c/jigmonitor/", providing that's the package you actually want.
The path of the compiled class for ReplyServer is not in the classpath of your JVM. You can check this by looking at the classpath used to start your JVM and seeing if the class is actually there or not. In most generic setups servlet setups there will be a "WEB-INF/classes" folder for you to go poke around in.
Good luck!
(The link David posted gives a ton of information on this type of issue and the possible causes. I would recommend tucking that away for later)
Is there any way to compile a java program without having the java file name with its base class name.
If so, please explain..
To answer the question take a look at this example:
Create a file Sample.java
class A
{
public static void main(String args[])
{
String str[] = {""};
System.out.println("hi");
B.main(str);
}
}
class B
{
public static void main(String args[])
{
System.out.println("hello");
}
}
now you compile it as javac Sample.java and run as java A then output will be
hi
hello
or you run as java B then output will be hello
Notice that none of the classes are marked public therefore giving them default access. Files without any public classes have no file naming restrictions.
Your Java file name should always reflect the public class defined within that file. Otherwise, you will get a compiler error. For example, test.java:
public class Foo {}
Trying to compile this gives:
[steven#scstop:~]% javac test.java
test.java:1: class Foo is public, should be declared in a file named Foo.java
public class Foo {
^
1 error
So you must have your filename match your public class name, which seems to render your question moot. Either that or I don't understand what you're asking... spending some time explaining what you are actually trying to achieve would go a long way towards asking a more effective question :)
As long as you don't have a public class in your source file, you can name your source file to any name and can compile. But, if you have a public class in your source file, that file should have the name same as your class name. Otherwise, compiler will throw an error.
Example:
Filename: TestFileName.java
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello,World\n");
}
}
Compiling: javac TestFileName.java
Error:
TestFileName.java:1: class HelloWorld is public, should be declared in a file named HelloWorld.java
public class HelloWorld
^
1 error
No, the public class name must match the file name. Inner, non public, class names may differ.
You must have a public class with the same name as the file name. This is a Very Good Thing. You CAN have secondary classes inside the same file as long as they are not public. They can still be "default" though, so they can still be used by other classes in the same package.
This should not be done for the most part. Java's naming patterns regarding classes and packages are one of the bigger advantages it has--makes a programmers life easier at no cost.
You can use the Java Compile API and compile any java source you wish, the source need not come from a file or could come from a file with an unrelated name. It depends on how obtuse you want to develop your program. ;)
yes, we compile a java file with a different name than the class, provided that there should not be any public class in that file.
If there is any public class in file then in that case you have to give that name as file name. But if your class does not contain any public class then you can give any name to you class.
Please refer below example to make it more clear:
file name : sample.java
class A
{
public static void main(String args[])
{
System.out.println("hi in Class A");
}
}
class B
{
public static void main(String args[])
{
System.out.println("hello in class B");
}
}
then compile it with(windows) : javac sample.java
then run it : java A
output : hi in Class A
then run it : java B
output : hello in class B
Please check and confirm.
It is not necessary to name your file same as the name of the class it has, until this class is public. Though it is a good practice to name the file same as the name of class.
The compiler will compile your file successfully and make a dot class file. Now at the run time you need to give class name to the JVM for that you have to keep the name of the class, which has main method, in your mind. If you keep both the file name and the class name same, it will become easy to remember the name of the compiled dot class file.
for example:
file Dummy.java
class Dummy
{
public static void main(String args[])
{
System.out.println("This is Dummy class running");
}
}
to run the above code we will use :
Javac Dummy.java // to compile
Java Dummy //to run
example:
file Dummy.java
class Diff
{
public static void main(String args[])
{
System.out.println("This is Diff class running");
}
}
to run the above code we will use :
Javac Dummy.java // to compile
Java Diff //to run
I guess what he means is the .java file is named differently than the actual class defined inside it.
I guess this is not possible.
No. You could write a shell script to rename the .java file before compiling it, but javac requires that filenames = class names.
(Also in windows, it's case insensitive, so ASDF.java can compile Asdf.class)
yes, you can choose any name for the file (.java). there is no matter to what are the name of classes in that file means that class names may be totaly different from the file name.
you should compile the program with file name and you should run the program with the class name in which the main method exist.
main methods may be multiple in different classes so you should run it with the class name in which the main method you want to run......
we can save the file tootle different name of class name because in java we compile the program but we run the method.
we have to compile our program with file name and run our class name
Yes,it is possible to compile a java source file with different file name but you need to make sure none of the classes defined inside are public...when you compile the source file the corresponding .class files for the classes inside the source file are created.
Yes,you can save your java source code file with any other name, not same as your main class name but when you comiple it than byte code file name will be same as your main class name. So for your ease of not to memorize to many names for java code run, You need to have your file name same as your main class than only your file name and byte code file will be with same name.
If class is not public you can save it using other name like if classname is Simple then save it Hard.java.
complie->Hard.java
run->Simple.java
Save your java file by .java only.
compile javac .java
run java yourclassname
For example if my program main class name is A then
save by .java only
compile by javac .java
run by java A
yes, we can compile a java file with a different name than the class, provided that there should not be any public class in that file.
If there is any public class in file then in that case you have to give that name as file name. But if your class does not contain any public class then you can give any name to you class.
Please refer below example to make it more clear:
file name : example.java
class A
{
public static void main(String args[])
{
System.out.println("You are in Class A");
}
}
class B
{
public static void main(String args[])
{
System.out.println("You are in class B");
}
}
then compile it with : javac example.java
then run it : java A
output : you are in Class A
then run it : java B
output : you are in class B
Please check and confirm.
You can write more than one main methods in java because java provides main method overloading in which main method can also be overloaded . Once you compile the file here example.java
Compiler create .class file which contains main method when you run the file with java A it will run the A.class file whih contains the main method of class A and that output will be display on you screen ,but when you run this file with java B ,It runs the B.class file which provides main method of B class
So your code is run successfully
Yes. This can be done.
The main reason for the class and file name to be same are to make the job of the complier easy to check which class it needs to run, in the whole list of the Java classes.
So it's a good practice to have filename and class name as same.
And you have compile and run a class with different name other than the filename, If you don't have any public methods in this class.
By convention, the name of the main class should match the name of the file that holds the program. You should also make sure that the capitalization of the filename matches the class name.
The convention that filenames correspond to class names may seem arbitrary. However, this convention makes it easier to maintain and organize your programs. Furthermore, in some cases, it is required.
According to the other answers the only viable solution is to somehow determine the classname from the source, then use it to rename the file to proper name and compile it as usual.
Another option is to alter the package and class name in the source to match file name:
sed -i -r "0,/package/s/^\s*package .*?;/package new.klass.pkg;/" %1
sed -i -r "0,/class/s/public\s+class .+?\{/public class NewClassName {/" %1
Via How to use sed to replace only the first occurrence in a file?
You can have your java file even without name ( simply ".java" ). Only thing is you should not have any public class in your file.