Question

NetBeans do not accept my code. Why? See the pic.

Answer 1

You need to change the code from

package org.demo.myfilter;

import org.demo.textfilter.TextFilter;

@ServiceProvider(service=TextFilter.class)
public class UpperCaseFilter implements TextFilter {

    public String process(String s) {
        return s.toUpperCase();
    }

}

into

package org.demo.myfilter;

import org.demo.textfilter.TextFilter;
import org.openide.util.lookup.ServiceProvider;

@ServiceProvider(service=TextFilter.class)
public class UpperCaseFilter implements TextFilter {

    public String process(String s) {
        return s.toUpperCase();
    }

}

Note: You can leverage the Fix Imports item from the Source menu (CTRL-SHIFT-I/Clover-SHIFT-I) to take care of the second one automatically, if you have declared the dependeny between your module and the NetBeans platform Utilities API module