In NetBeans IDE 7.2, a new wizard will be found in the "Module Development" category in the New File dialog, for creating new Java Hints.

1. Select a package in a NetBeans module project. Right click, choose New/Other.../Module Development/Java Hint:
   
   
   
   You'll then see this:
   
   
   
   
2. Fill in:
   
   • Class Name: the name of the class that should be generated. E.g. "Example".
     
     
   • Hint Display Name: the display name of the hint itself (as will appear in Tools/Options). E.g. "Example Hint".
     
     
   • Warning Message: the warning that should be produced by the hint. E.g. "Something wrong is going on".
     
     
   • Hint Description: a longer description of the hint, will appear in Tools/Options and eventually some other places. E.g. "This is an example hint that warns about an example problem."
     
     
   • Will also provide an Automatic Fix: whether the hint will provide some kind of transformation. E.g. "yes".
     
     
   • Fix Display Name: the display name of such a fix/transformation. E.g. "Fix the problem".
     
     
3. Click Finish.
   
   
   • Should generate "Example.java", the hint itself:
     

     import com.sun.source.util.TreePath;
     import org.netbeans.api.java.source.CompilationInfo;
     import org.netbeans.spi.editor.hints.ErrorDescription;
     import org.netbeans.spi.editor.hints.Fix;
     import org.netbeans.spi.java.hints.ConstraintVariableType;
     import org.netbeans.spi.java.hints.ErrorDescriptionFactory;
     import org.netbeans.spi.java.hints.Hint;
     import org.netbeans.spi.java.hints.HintContext;
     import org.netbeans.spi.java.hints.JavaFix;
     import org.netbeans.spi.java.hints.TriggerPattern;
     import org.openide.util.NbBundle.Messages;
     
     @Hint(displayName = "DN_com.bla.Example",
     description = "DESC_com.bla.Example",
     category = "general") //NOI18N
     @Messages({"DN_com.bla.Example=Example Hint",
         "DESC_com.bla.Example=This is an example hint that warns about an example problem."})
     
     public class Example {
     
         @TriggerPattern(value = "$str.equals(\"\")", //Specify a pattern as needed
         constraints =
         @ConstraintVariableType(variable = "$str", type = "java.lang.String"))
         @Messages("ERR_com.bla.Example=Something wrong is going on")
         public static ErrorDescription computeWarning(HintContext ctx) {
             Fix fix = new FixImpl(ctx.getInfo(), ctx.getPath()).toEditorFix();
             return ErrorDescriptionFactory.forName(ctx, ctx.getPath(), Bundle.ERR_com.bla_Example(), fix);
         }
     
         private static final class FixImpl extends JavaFix {
     
             public FixImpl(CompilationInfo info, TreePath tp) {
                 super(info, tp);
             }
     
             @Override
             @Messages("FIX_com.bla.Example=Fix the problem")
             protected String getText() {
                 return Bundle.FIX_com_bla_Example();
             }
     
             @Override
             protected void performRewrite(TransformationContext ctx) {
                 //perform the required transformation
             }
     
         }
     
     }
     

   • Should also generate "ExampleTest.java", a test for it. Unfortunately, the wizard infrastructure is not capable of handling changes related to test dependencies. So the ExampleTest.java has a todo list at its begining:
     

     /* TODO to make this test work:
      - add test dependency on Java Hints Test API (and JUnit 4)
      - to ensure that the newest Java language features supported by the IDE are available,
         regardless of which JDK you build the module with:
      -- for Ant-based modules, add "requires.nb.javac=true" into nbproject/project.properties
      -- for Maven-based modules, use dependency:copy in validate phase to create
         target/endorsed/org-netbeans-libs-javacapi-*.jar and add to endorseddirs
         in maven-compiler-plugin configuration
      */

     Warning: if this is a project for which tests never existed before, you may need to close&reopen the project, so that "Unit Test Libraries" node appears - a bug in apisupport projects, as far as I can tell. 

Thanks to Jan Lahoda for the above rough guide.