The “Could Not Find or Load Main Class” in Java error typically occurs when the Java Virtual Machine (JVM) cannot find the specified main class that should be executed. This error commonly arises when running a Java application or a JAR file.

Here are examples of each reason for the "Could not find or load main class" error in Java, along with their respective solutions:

 

1.    Version mismatch:

first check your java compiler version and Java JRE Version.
here is steps:

·       Project -> Clean

·       Right-Click Project -> Properties -> Java Build Path -> Libraries -> one click one JRE system… -> click on edit -> click on Installed JRE -> click on Add and add your jdk path for example “C:\Program Files\Java\jdk-11” then select and Apply -> Apply and close.


 

·       Change compiler version as per JRE version
in above example jdk-11 for JRE so compiler is also Java compiler 11.
Right-Click Project -> Properties -> Java Compiler -> change other to 11 and apply -> apply and close.

 

 


2.    Incorrect command or classpath:

Example command: java MyClass

 

Solution: Ensure that the class name is specified correctly, including the package name if applicable. For example, if the class is in the com.example package, use java com.example.MyClass.

 

3.    Missing or incorrect class file:

Example command: java MyClass

 

Error: ‘Error: Could not find or load main class MyClass’

Solution: Verify that the class file MyClass.class exists in the current directory or the specified classpath. If it is missing or located elsewhere, compile the Java file again using javac and provide the correct path.

 

4.    Compilation errors:
           public class MyClass {

    public static void main(String[] args) {

        System.out.println("Hello, World!")

    }

}

Error: MyClass.java:4: error: ';' expected

 

Solution: Fix the compilation error by adding a semicolon at the end of the println statement: System.out.println("Hello, World!");.

 

5.    Package structure:
          package com.example;

 

public class MyClass {

    public static void main(String[] args) {

        System.out.println("Hello, World!");

    }

}

Example command: java MyClass

 

Error: ‘Error: Could not find or load main class MyClass’

Solution: Make sure the file is located in the correct directory according to the package structure. In this case, the file should be placed in the com/example directory and executed using java com.example.MyClass.

 

6.    Jar file issues:
           Example command: java -jar myprogram.jar

Error: Error: ‘Could not find or load main class com.example.MyClass’

Solution: Ensure that the JAR file is created correctly, including the manifest file with the correct Main-Class entry. For example, the manifest file should contain Main-Class: com.example.MyClass. Rebuild the JAR file if necessary.

 

By addressing these potential causes, you can resolve the Could Not Find or Load Main Class in Java error and successfully run your Java application or JAR file.