자바에러 - import 잘 안될때

I have also gone through the same error but it was resolved just by changing some properties of the project:

• Right-click on your project
• Click on Properties
• Select Java Build Path from right-hand side panel
• Select Order and Export tab
• Click on your JRE System Library or JDK Library
• Click on Up button and move it to first position
• Click Ok
• Clean & build your project.

Do repeat this for all other dependents project as well, if you have dependencies.

It resolved my issue because previously the Java files were picking other libraries and packages not from JRE package as it was ordered set in last priority.