Unable to import javax.swing.JFrame

When you make a new java project at JRE choose "Use an execution environment JRE and from there select JavaSE-1.7 or 1.8 and just should solve the problem. I had the same problem like you before.

1. Right-click on the project
2. Select properties
3. Java build path
4. Library > Add Library > Add JRE SYSTEM Library
5. Execution Environment
6. Select JavaSE-1.7
7. Finish

Just add requires java.desktop; to your module-info.java file.

module-info.java:

module your_project_name{
    requires java.desktop;
}