A popular error message for new Java users.
Error: Could not find or load main class ClassName.class
Caused by: java.lang.ClassNotFoundException: ClassName.class
1. No Package
1.1 Reviews a simple Java Hello World, no package.
C:\projects\HelloWorld.java
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World");
}
}
Terminal
# Compile Java source code
C:\projects> javac HelloWorld.java
C:\projects> dir
15/04/2019 01:20 PM 425 HelloWorld.class
15/04/2019 01:42 PM 138 HelloWorld.java
# Run Java
C:\projects>java HelloWorld.class
Error: Could not find or load main class HelloWorld.class
Caused by: java.lang.ClassNotFoundException: HelloWorld.class
To fix it, run java ClassName, without .class extension.
Terminal
C:\projects>java HelloWorld
Hello World
2. With Package
2.1 A simple Hello World and package it as com.mkyong
C:\projects\HelloWorld.java
package com.mkyong;
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World");
}
}
Terminal
# Compile Java source code
C:\projects> javac HelloWorld.java
C:\projects> dir
15/04/2019 01:20 PM 425 HelloWorld.class
15/04/2019 01:42 PM 138 HelloWorld.java
C:\projects>java HelloWorld
Error: Could not find or load main class HelloWorld
Caused by: java.lang.NoClassDefFoundError: com/mkyong/HelloWorld (wrong name: HelloWorld)
2.2 If package is defined, the Java classes .class must place in the correct folder location.
For example :
C:\projects\HelloWorld.java
package com.mkyong;
The above generated class file must place in C:\projects\com\mkyong\HelloWorld.class
2.3 To fix it, we can use -d to specify where to place generated class files.
Terminal
# Compile Java source code
C:\projects> javac -d . HelloWorld.java
C:\projects> dir
15/04/2019 02:01 PM <DIR> com
15/04/2019 01:51 PM 161 HelloWorld.java
C:\projects\com\mkyong\HelloWorld.class
C:\projects\HelloWorld.java
2.4 Now, we can run like this java {package}.HelloWorld
Terminal
C:\projects>java HelloWorld
Error: Could not find or load main class HelloWorld
Caused by: java.lang.ClassNotFoundException: HelloWorld
C:\projects>java com.mkyong.HelloWorld
Hello World
Sharing same issue I faced in Eclipse. If you ever faced this then what should you Do?
Here is simple 3 steps which can solve this error.
a) JRE Library
b) Selenium Server Standalone
After selection and Saving them it will RUN your program and Error will Resolved.
root@localhost:/LIST/Test1#java JTableDemo12
Error: Could not find or load main class JTableDemo12
Caused by:java.lang.NoClassDefFoundError: com/mykong/JTableDemo12 (wrong name: JTableDemo12)
root@localhost:/LIST/Test1# java com.mykong.JTableDemo12
Error: Could not find or load main class com.mykong.JTableDemo12 Caused by: java.lang.ClassNotFoundException: com.mykong.JTableDemo12
Thank you so much. I looked at 17 other websites and could not figure it out but your solution worked.
Thank you man!
Thank you. I search too many site for this error. Your solution is ok.
Many thanks for your Help, but in my case I was seeing the error line only and not Caused by line
How did you make the Caused by line appears after the error line ?
thanks
Thanks you are the best Mkyong ^^