NetBeans Code Completion Tutorial

Last reviewed on 2022-02-02

This tutorial shows you how to implement the Editor Code Completion API. You will be shown how to implement the API in the context of HTML files. When the user invokes the code completion feature, a code completion box will appear, displaying words that can complete the text typed in the editor. At the end of this tutorial, HTML files will have a code completion box as follows:

The content of the code completion box will come from country names retrieved from the JDK’s java.util.Locale package.

For troubleshooting purposes, you are welcome to download the completed tutorial source code.

Introduction to Code Completion Integration

Two classes apply to code completion and these will be developed in this tutorial:

Both of these come from the Editor Code Completion API and are implemented in this tutorial’s module as CountriesCompletionItem and CountriesCompletionProvider.

Creating the Module Project

In this section, we use a wizard to create the source structure that every NetBeans module requires. The source structure consists of certain folders in specific places and a set of files that are always needed. For example, every Ant-based NetBeans module requires a nbproject folder, which holds the project’s metadata.

  1. Choose File > New Project Ctrl+Shift+N. Under Categories, select NetBeans Modules. Under Projects, select Module. Click Next.

  2. In the Name and Location panel, type CountryCodeCompleter in Project Name. Change the Project Location to any directory on your computer. Click Next.

  3. In the Basic Module Configuration panel, type org.netbeans.modules.countries as the Code Name Base. Click Finish.

The IDE creates the CountryCodeCompleter project. The project contains all of your sources and project metadata, such as the project’s Ant build script. The project opens in the IDE. You can view its logical structure in the Projects window Ctrl+1 and its file structure in the Files window Ctrl+2.

Implementing the Completion Provider Class

The first class we will deal with when creating a code completion feature for HTML files is the CompletionProvider. As the user types in an editor, the code completion infrastructure asks all code completion providers registered in the XML layer file to create CompletionTasks. The tasks are created by the CompletionProvider.createTask method. What happens when the method is invoked is up to the implementation. In our implementation, we will create a CompletionItem for a list of countries.

  1. Right-click the LIbraries node of the CountryCodeCompleter project and choose Add Module Dependency:

    cc 72 deps

    Set dependencies on the following:

    • "Editor Code Completion", which provides the API classes that we need in this tutorial.

    • "MIME Lookup API", which provides the Java annotation for registering completion providers.

    • "Utilities API".

    • "Base Utilities API".

  2. Right-click the CountryCodeCompleter project and choose New > Java Class. In Class Name, type CountriesCompletionProvider . In Package, choose org.netbeans.modules.countries. Click Finish.

  3. In the CountriesCompletionProvider class, change the signature so that the class implements CompletionProvider. Place the cursor on the line that defines the signature. A lightbulb appears. Click it and the IDE adds an import statement for org.netbeans.spi.editor.completion.CompletionProvider. The lightbulb appears again. Click it again and the IDE creates skeleton methods for the two methods required by the CompletionProvider class. You should now see this:

    package org.netbeans.modules.countries;

import javax.swing.text.JTextComponent;
import org.netbeans.spi.editor.completion.CompletionProvider;
import org.netbeans.spi.editor.completion.CompletionTask;

public class CountriesCompletionProvider implements CompletionProvider {

    public CountriesCompletionProvider() {
    }

    @Override
    public CompletionTask createTask(int queryType, JTextComponent jtc) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    @Override
    public int getAutoQueryTypes(JTextComponent component, String typedText) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

}

  4. Before coding the CompletionProvider class, let’s register it in the XML layer file, via a NetBeans Platform annotation:

    package org.netbeans.modules.countries;

import javax.swing.text.JTextComponent;
import org.netbeans.api.editor.mimelookup.MimeRegistration;
import org.netbeans.spi.editor.completion.CompletionProvider;
import org.netbeans.spi.editor.completion.CompletionTask;

@MimeRegistration(mimeType = "text/html", service = CompletionProvider.class)
public class CountriesCompletionProvider implements CompletionProvider {

    @Override
    public CompletionTask createTask(int queryType, JTextComponent jtc) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    @Override
    public int getAutoQueryTypes(JTextComponent component, String typedText) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

}

    Read @MimeLocation, @MimeRegistration and @MimeRegistrations added for details on the annotation above.

Implementing the createTask Method

In this section we create a skeleton implementation of AsyncCompletionTask. In the next sections, we will fill this skeleton method out.

  1. In the createTask method, below the code from the previous section, add the following lines:

    return new AsyncCompletionTask(new AsyncCompletionQuery() {
});

    Here, we’re returning AsyncCompletionTask , which will allow for the asynchronous creation of our task. The class comes from the org.netbeans.spi.editor.completion.support package, which provides several useful supporting classes for code completion implementations. We will use several of them in this tutorial.

  2. Place the cursor on the line. Click the lightbulb that appears and let the IDE add import statements. Also let it create a skeleton method for the query method.

  3. Next, we need to specify which code completion type we are working with. When the user clicks Ctrl+Space, or an alternative key combination defined by the user, our code completion entries should appear. This is the COMPLETION_QUERY_TYPE. Alternative query types exist, such as DOCUMENTATION_QUERY_TYPE and TOOLTIP_QUERY_TYPE. We need to test whether the user pressed the keys applicable to the COMPLETION_QUERY_TYPE. Therefore add the following test to the start of the createTask method:

    if (queryType != CompletionProvider.COMPLETION_QUERY_TYPE)
   return null;

    At this stage, the createTask method should look as follows:

    @Override
public CompletionTask createTask(int queryType, JTextComponent jtc) {

    if (queryType != CompletionProvider.COMPLETION_QUERY_TYPE)
        return null;

    return new AsyncCompletionTask(new AsyncCompletionQuery() {
        protected void query(CompletionResultSet completionResultSet, Document document, int caretOffset) {
        }
    });

}

Implementing the getAutoQueryTypes Method

In this section we return 0 as our AutoQueryType , so that the code completion box does not appear automatically, but only when requested by the user.

Before filling out the query method, let’s look at the getAutoQueryTypes(JTextComponent jTextComponent, String string) method. This method determines whether the code completion box appears automatically or not. For now, let’s return 0. This means that the code completion box will never appear unless the user explicitly asks for it. So, this method should now look as follows:

@Override
public int getAutoQueryTypes(JTextComponent component, String string) {
    return 0;
}

By default, the user would press Ctrl+Space to make the code completion box appear. Later, we can add a new option to our Options window extension, such as a checkbox which will change the int returned in this method from 0 to 1, so that the code completion box appears automatically. (There are also other types of queries, as shown here.)

Implementing the Completion Item Class

In this section we will create a class that implements CompletionItem . Once we have defined this class, we will fill out the query method in the CompletionProvider class. The CompletionProvider will create instances of our CompletionItem .

  1. Right-click the CountryCodeCompleter project and choose New > Java Class. In Class Name, type CountriesCompletionItem . In Package, choose org.netbeans.modules.countries . Click Finish.

  2. We will return to this class in later steps. For now, we will fill out the query method that we defined in the CompletionProvider class. Fill out the AsyncCompletionTask as follows, and note the explanatory comments in the code:

    return new AsyncCompletionTask(new AsyncCompletionQuery() {

    @Override
    protected void query(CompletionResultSet completionResultSet, Document document, int caretOffset) {

        //Iterate through the available locales
        //and assign each country display name
        //to a CompletionResultSet:
        Locale[] locales = Locale.getAvailableLocales();
        for (int i = 0; i < locales.length; i++) {
            final Locale locale = locales[i];
            final String country = locale.getDisplayCountry();
            if (!country.equals("")) {
                completionResultSet.addItem(new CountriesCompletionItem(country, caretOffset));
            }
        }

        completionResultSet.finish();
    }

}, jtc);

    A red underline remains, after you let the IDE add various import statements. The error underline tells you that the CompletionItem’s constructor does not expect the values that you are passing to it. In the next step, we will fill out the CompletionItem so that it meets the requirements of the CompletionProvider.

    Read Java Classes in Code Completion to learn how to put Java classes in the code completion box, instead of the locales that are used above.

  3. In the CountriesCompletionItem class, change the signature so that the class implements CompletionItem . Let the IDE create import statements and skeleton implementations for the class’s required methods. Read the entry in the NetBeans Javadoc for CompletionItem to begin to understand what each of the methods is for. For now, we will implement a minimal completion item, just enough to be able to compile the module and see the code completion box.

  4. In the CountriesCompletionItem class, define the constructor as follows:

    private String text;
private static ImageIcon fieldIcon =
        new ImageIcon(ImageUtilities.loadImage("org/netbeans/modules/countries/icon.png"));
private static Color fieldColor = Color.decode("0x0000B2");
private int caretOffset;

public CountriesCompletionItem(String text, int caretOffset) {
    this.text = text;
    this.caretOffset = caretOffset;
}

    Note that here we’re referencing an icon. This is the icon that will appear next to each entry represented by the CompletionItem in the code completion box. The icon can be any icon with a dimension of 16x16 pixels. For example, you could make use of this icon: cc icon

    If you like, you can right-click the image above and save it to the location specified in the ImageIcon definition above.

  5. Next define the getPreferredWidth() and render() methods as follows:

    @Override
public int getPreferredWidth(Graphics graphics, Font font) {
    return CompletionUtilities.getPreferredWidth(text, null, graphics, font);
}

@Override
public void render(Graphics g, Font defaultFont, Color defaultColor,
        Color backgroundColor, int width, int height, boolean selected) {
    CompletionUtilities.renderHtml(fieldIcon, text, null, g, defaultFont,
            (selected ? Color.white : fieldColor), width, height, selected);
}

    Define the getSortText() method as follows:

    @Override
public CharSequence getSortText() {
    return text;
}

    Next, define the getInsertPrefix() method:

    @Override
public CharSequence getInsertPrefix() {
    return text;
}

    Finally, create dummy implementations of the remaining methods. So, return null for createDocumentationTask() and createToolTipTask() . Then return false for instantSubstitution() and return 0 for getSortPriority() . Finally, empty the methods defaultAction and processKeyEvent .

  6. Right-click the module and choose Run. A new instance of the IDE starts up and installs your module. Open an HTML file in the IDE. Type something and press Ctrl-Space. You should now see the following:

    cc 72 result 1

    When you press Enter in the list above, nothing happens. That is because we have not defined the defaultAction() method yet. We will do so in the next section. Also note that the list does not narrow while you are typing. That is because we have not created a filter yet. The filter will detect what we are typing and adjust the entries in the list accordingly. We will create a filter in a later section.

Implementing the Action

In this section we specify what happens when the user presses the Enter key or clicks the mouse over an entry in the code completion box.

  1. Fill out the defaultAction() method as follows:

    @Override
public void defaultAction(JTextComponent jtc) {
    try {
        StyledDocument doc = (StyledDocument) jtc.getDocument();
        doc.insertString(caretOffset, text, null);
        //This statement will close the code completion box:
        Completion.get().hideAll();
    } catch (BadLocationException ex) {
        Exceptions.printStackTrace(ex);
    }
}

  2. Install the module again. Notice that when you press Enter or click the mouse over an entry in the code completion box, the selected text is added at the cursor in your HTML file. However, the text that you typed prior to calling up the code completion box is not removed. Below, the "V" should be removed, because "Vietnam" was selected from the code completion box:

    cc 65 result of cc2

    In the next section, we will add functionality to detect the number of characters that have been typed and remove them when the selected country is inserted into the document.

Implementing the Filter

In this section we enable the code completion box to narrow while the user is typing. In this way, when the user types 'hel', only words that begin with those letters are shown in the code completion box. The filter is defined in the CountriesCompletionProvider class.

  1. In the CountriesCompletionProvider class, rewrite the AsyncCompletionTask() method by adding the statements highlighted in bold below:

    return new AsyncCompletionTask(new AsyncCompletionQuery() {

    @Override
    protected void query(CompletionResultSet completionResultSet, Document document, int caretOffset) {

        String filter = null;
        int startOffset = caretOffset - 1;

        try {
            final StyledDocument bDoc = (StyledDocument) document;
            final int lineStartOffset = getRowFirstNonWhite(bDoc, caretOffset);
            final char[] line = bDoc.getText(lineStartOffset, caretOffset - lineStartOffset).toCharArray();
            final int whiteOffset = indexOfWhite(line);
            filter = new String(line, whiteOffset + 1, line.length - whiteOffset - 1);
            if (whiteOffset > 0) {
                startOffset = lineStartOffset + whiteOffset + 1;
            } else {
                startOffset = lineStartOffset;
            }
        } catch (BadLocationException ex) {
            Exceptions.printStackTrace(ex);
        }

        //Iterate through the available locales
        //and assign each country display name
        //to a CompletionResultSet:
        Locale[] locales = Locale.getAvailableLocales();
        for (int i = 0; i < locales.length; i++) {
            final Locale locale = locales[i];
            final String country = locale.getDisplayCountry();
            //Here we test whether the country starts with the filter defined above:
            if (!country.equals("") && country.startsWith(filter)) {
                //Here we include the start offset, so that we'll be able to figure out
                //the number of characters that we'll need to remove:
                completionResultSet.addItem(new CountriesCompletionItem(country, startOffset, caretOffset));
            }
        }
        completionResultSet.finish();

    }

}, jtc);

  2. Right at the end of the CountriesCompletionProvider, add the following two methods:

    static int getRowFirstNonWhite(StyledDocument doc, int offset)
throws BadLocationException {
    Element lineElement = doc.getParagraphElement(offset);
    int start = lineElement.getStartOffset();
    while (start + 1 < lineElement.getEndOffset()) {
        try {
            if (doc.getText(start, 1).charAt(0) != ' ') {
                break;
            }
        } catch (BadLocationException ex) {
            throw (BadLocationException)new BadLocationException(
                    "calling getText(" + start + ", " + (start + 1) +
                    ") on doc of length: " + doc.getLength(), start
                    ).initCause(ex);
        }
        start++;
    }
    return start;
}
    static int indexOfWhite(char[] line){
    int i = line.length;
    while(--i > -1){
        final char c = line[i];
        if(Character.isWhitespace(c)){
            return i;
        }
    }
    return -1;
}

  3. Change the constructor of the CountriesCompletionItem to receive the start offset. Then change the defaultAction so that the start offset will be used in determining the characters that will be removed when the selected country is inserted.

    Below, the statements that should be added: private int dotOffset;

    public CountriesCompletionItem(String text, int dotOffset, int caretOffset) {
    this.text = text;
    this.dotOffset = dotOffset;
    this.caretOffset = caretOffset;
}

@Override
public void defaultAction(JTextComponent component) {
    try {
        StyledDocument doc = (StyledDocument) component.getDocument();
        //Here we remove the characters starting at the start offset
        //and ending at the point where the caret is currently found:
        doc.remove(dotOffset, caretOffset-dotOffset);
        doc.insertString(dotOffset, text, null);
        Completion.get().hideAll();
    } catch (BadLocationException ex) {
        Exceptions.printStackTrace(ex);
    }
}

...
...
...

  4. Install the module again and notice that this time the list of words narrows while you are typing…​

    cc 65 result of cc

    …​and that when you press Enter, the characters that you typed are removed and replaced by the country selected from the code completion box.

Implementing the Tooltip and Documentation Task

Some optional features can also be added, as described below.

  1. Optionally, you can implement the createToolTipTask method in the CountriesCompletionItem , with this result when Ctrl-P is pressed:

    cc 65 result of cc3

    Here is the code that will achieve the result shown in the screenshot above:

    @Override
public CompletionTask createToolTipTask() {
    return new AsyncCompletionTask(new AsyncCompletionQuery() {
        @Override
        protected void query(CompletionResultSet completionResultSet, Document document, int i) {
            JToolTip toolTip = new JToolTip();
            toolTip.setTipText("Press Enter to insert \"" + text + "\"");
            completionResultSet.setToolTip(toolTip);
            completionResultSet.finish();
        }
    });
}

  2. Optionally, you can provide documentation for the entries in the code completion box:

    cc 65 result of cc4

    Make use of the documentation box like this, by implementing the createDocumentationTask method in the CountriesCompletionItem class:

    @Override
public CompletionTask createDocumentationTask() {
    return new AsyncCompletionTask(new AsyncCompletionQuery() {
        @Override
        protected void query(CompletionResultSet completionResultSet, Document document, int i) {
            completionResultSet.setDocumentation(new CountriesCompletionDocumentation(CountriesCompletionItem.this));
            completionResultSet.finish();
        }
    });
}

    In the code above, the reference to the CountriesCompletionDocumentation class could be implemented as follows:

    public class CountriesCompletionDocumentation implements CompletionDocumentation {

    private CountriesCompletionItem item;

    public CountriesCompletionDocumentation(CountriesCompletionItem item) {
        this.item = item;
    }

    @Override
    public String getText() {
        return "Information about " + item.text;
    }

    @Override
    public URL getURL() {
        return null;
    }

    @Override
    public CompletionDocumentation resolveLink(String string) {
        return null;
    }

    @Override
    public Action getGotoSourceAction() {
        return null;
    }

}

    By implementing the getURL() in the code above, you can enable the URL button, as shown below:

    cc 65 result of cc5

    When the user clicks the URL button, the browser set in the IDE will open, displaying the content provided by the specified URL.

Congratulations, you have now completed a simple implementation of a code completion integration module.

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See Also

For more information about creating and developing plugins, see the following resources: