1. Create class 'SimpleClass' and insert this code:

  //---------------------------
  import java.io.File;

  public class SimpleClass{
    
      public void method() {
          File f = new File("abc");
      }
    
  }
  //---------------------------

2. Select 'SimpleClass'

3. Go to Refactor->Extract Superclass...

4. Set Superclass Name: 'AnotherClass', check method 'simpleMethod()', than press Refactor

5. Now SimpleClass looks like this:

  //---------------------------
  import java.io.File;

  public class SimpleClass extends AnotherClass{
    
  }
  //---------------------------

>> import java.io.File; should be deleted

Product Version: NetBeans IDE 7.3.1 (Build 201306052037)
Java: 1.7.0_25; Java HotSpot(TM) 64-Bit Server VM 23.25-b01
Runtime: Java(TM) SE Runtime Environment 1.7.0_25-b30
System: Windows 7 version 6.1 running on amd64; Cp1252; en_US (nb)