Caused by java lang classnotfoundexception helloworld class

Java — не удалось найти или загрузить основной класс

Популярное сообщение об ошибке для новых пользователей Java.

 Error: Could not find or load main class ClassName.class Caused by: java.lang.ClassNotFoundException: ClassName.class 

1. Нет пакета

1.1 Обзоры простой Java Hello World, без пакета.

 # 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 

Чтобы исправить это, запустите java ClassName без .class расширение.

 C:projects>java HelloWorld Hello World 

2. С пакетом

2.1 Простой Hello World и package это так же как com.mkyong

 package com.mkyong; public class HelloWorld < public static void main(String[] args) < System.out.println("Hello World"); >> 

 # 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 Если package определяется, классы Java .class должен разместить в правильном месте папки.

Выше сгенерированный файл класса должен поместить в C:projectscommkyongHelloWorld.class

2.3 Чтобы исправить это , мы можем использовать -d указать, где разместить сгенерированные файлы классов.

 # Compile Java source code C:projects> javac -d . HelloWorld.java C:projects> dir 15/04/2019 02:01 PM com 15/04/2019 01:51 PM 161 HelloWorld.java C:projectscommkyongHelloWorld.class C:projectsHelloWorld.java 

2.4 Теперь мы можем бежать так java .HelloWorld

 C:projects>java HelloWorld Error: Could not find or load main class HelloWorld Caused by: java.lang.ClassNotFoundException: HelloWorld C:projects>java com.csharpcoderr.HelloWorld Hello World 

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Java – Could not find or load main class

To fix it, run java ClassName , without .class extension.

 C:\projects>java HelloWorld Hello World 

2. With Package

2.1 A simple Hello World and package it as com.mkyong

 package com.mkyong; public class HelloWorld < public static void main(String[] args) < System.out.println("Hello World"); >> 

 # 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.

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.

 # Compile Java source code C:\projects> javac -d . HelloWorld.java C:\projects> dir 15/04/2019 02:01 PM 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 .HelloWorld

 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 

References

mkyong

Founder of Mkyong.com, love Java and open source stuff. Follow him on Twitter. If you like my tutorials, consider make a donation to these charities.

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IntelliJ: Error: Could not find or load main class, java.lang.ClassNotFoundException

As you can see the above class does not have any complication issues or syntax errors. There can be multiple reasons that you may get the error, below are some of the solutions that may work for you!

• Make sure that the class name is correct.
• Go to Menu: Build -> Re-Build Project.
• Remove .idea directory from your project and restart IDE.
• Go to Files: Invalidate Cache/ Restart.
• Check your project has a out folder, if not create one, example: /Users/code2care/IdeaProjects/java-examples/out
• Edit Build/Run Configurations and check if you have selected the correct Java class that has a main method.

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‘Could not find or load main class’ when running jar containing docker-java as dependency #1098

‘Could not find or load main class’ when running jar containing docker-java as dependency #1098

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1. Create basic gradle project with docker-java as a compile dependency
2. Add a simple HelloWorld main class
3. Run the gradle jar task
4. java -jar hello-world.jar

Exception thrown at startup is

Error: Could not find or load main class HelloWorld Caused by: java.lang.ClassNotFoundException: HelloWorld 

Removing docker-java from compile dependencies fixes the issue.

dependencies < compile( "com.github.docker-java:docker-java:3.0.14" ) >task helloWorld(type: Jar) < manifest < attributes 'Main-Class': 'HelloWorld' >baseName = 'hello-world' from < configurations.compile.collect < it.isDirectory() ? it : zipTree(it) >> with jar > 

Reproduced with jdk8, jdk9, jdk10
Tested with docker-java versions 3.0.6 , 3.0.14 , 3.1.0-rc-4

The text was updated successfully, but these errors were encountered:

I have exactly the same issue. After including the docker-java as a compile dependency java can’t load my main class from the fat jar with a SecurityException «Invalid signature file digest for Manifest main attributes». Actually the same happens when I try to add the docker-client library. The reason was that the library’s signature files were copied into the META-INF of my fat jar and it broke class loading of my main class. Here is the fix:

 jar < manifest < attributes( "Main-Class" to "sandbox.MainKt" ) >from(configurations.compile.get().map < if (it.isDirectory) it else zipTree(it) >) from(configurations.runtimeClasspath.get().map < if (it.isDirectory) it else zipTree(it) >) exclude("META-INF/*.SF", "META-INF/*.DSA", "META-INF/*.RSA") > 

@sedovalx I’m facing this same exact problem but I’m new to this, so I’m not sure how would I go about using your fix. Could you elaborate a little on how to implement your fix? Thanks in advance

@dwgabriel the code fragment above is from my Gradle build script. It describes the configuration of the jar task that can be run with ./gradlew jar . The task assembles an executable jar file that can be executed with java -jar my-app.jar .

Build scripts in Gradle typically named as build.gradle (if written in Groovy) or build.gradle.kts (in case of Kotlin).

Still broken in 3.2.6 , same steps to reproduce, add dep. docker-java , build a fat jar, run with java -jar fat.jar :

dependencies < . implementation("com.github.docker-java:docker-java:3.2.6") >tasks.withType  < manifest < attributes["Main-Class"] = "com.company.application.Main" >configurations["compileClasspath"].forEach < file: File ->from(zipTree(file.absoluteFile)) > > 

Is an obscure workaround enough to consider this issue closed?

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