IntelliJ: Why can't I use a class from external jar

1
votes

When I created the jar file I wrote the following java file:

package myjar;

public class MyClass {

    public static void hello() {
        System.out.println("hello");
    }

    public static void main(String[] args) {
        MyClass.hello();
    }
}
  1. I named the file MyClass.java.
  2. I created a class file by typing "javac src/main/java/myjar/MyClass.java"
  3. I generated a jar file by the command: "jar cvf myjar.jar src/main/java/myjar/MyClass.class"

Now, I took the jar file and added it to Project Structure. The name of the jar is 'myjar': enter image description here

and in the IDE I wrote "import myjar.MyClass" and the word 'myjar' was marked in red.

When I use 'MyClass.hello()' in the project, I get an error:

no main manifest

Do you know what I can to to load it successfully ?

2
javaintellij-ideajar
Does this jar have myjar package? If not, create one, you can't import from the default package: stackoverflow.com/questions/2193226/…. – CrazyCoder
Yes. As you can see, class MyClass is inside myjar package – CrazySynthax
Check the jar structure, it should have myjar/MyClass.class and no other directories above, it also should have myjar directory, not just MyClass.class file in the root of the jar. – CrazyCoder

2 Answers

2
votes

You can only import some classes from your libraries on classpath into a Java source file, not a contents of a whole Java archive (JAR) file. So if you have inside myjar.jar file class Foo.class inside package (folder) bar, you can do

import bar.Foo;
0
votes

After adding the .jar as a library in IntelliJ, you still need to add it to the module.

enter image description here

Then the library will appear in the module's list of dependencies.

enter image description here