Eclipse无法识别JFrame

Question

I am trying to create an example with JFrame, but when i write JFrame in eclipse, it gets underscored by red line as if it is not defined, how can I solve this issue:

code :

package openCVExamples;

public class OpenCVTest {

  public static void main(String[] args) {
    JFrame j = new JFrame();        
  }
} 

update :

when hover over JFrame keyword, eclipse says

:Access restriction: the type     
JFrame is not accessible due to restriction on required library 
c:?\programfiles\java\jre1.8.0_40\lib\rt.jar 

Answer 1

Most likely; you did not import the JFrame class.

You can simply press "ctrl-shift-o" to "organize" your import statements. Eclipse will automatically add all required imports.

JFrame is a class that belongs to the "default" set of classes for Java. If it can't be found/imported, then your "project setup" is broken somehow.

Answer 2

You have to import the JFrame class. You can write:

package OpenCVExamples;

import javax.swing.*;

public class OpenCVTest{
     //your code
}

at the top of your file, but after the package line.

You can also do it automatically by pressing Ctrl+Shift+O to import all the classes you need.

Answer 3

Project -> Properties -> Libraries

Remove the rt.jar file

Click on "Add external JARs.."

Re-add the rt.jar file (located at C:\\Program Files\\Java\\jre1.8.0_20\\lib)

If it still does not work, you might want to try a different Java Runtime Environment. I had the same problem and what fixed it for me was importing the rt.jar file located at C:\\Program Files\\Java\\jre7\\lib.