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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">

<!--

* Notice of copyright on this source code

* product does not indicate publication.

* RESTRICTED RIGHTS LEGEND: Use, duplication, or disclosure by

* the U.S. Government is subject to restrictions as set forth

* in subparagraph (c)(1)(ii) of the Rights in Technical Data

* and Computer Software Clause at DFARS 252.227-7013 (Oct. 1988)

* and FAR 52.227-19 (c) (June 1987).

* Sun Microsystems, Inc., 4150 Network Circle,

* Santa Clara, California 95054, U.S.A.

-->

<html>

<head>

<title>Creating Lightweight Java Components</title>

</head>

<h2>Creating Lightweight Java Components</h2>

<p>

This topic describes how you can create <a

href="lwcomp.html#lwcomp">lightweight Java components</a> and

add them to HTML topics using the HTML

<code><OBJECT></code> tag. The last section in this

topic contains references to supplemental information about

lightweight components and the HTML <code><OBJECT></code>

tag.

<p> <img src="../../images/hg_note.gif" width="18" height="13"> References to

supplemental information are included at the end of this topic.

<h3>Lightweight Components for HTML Topics</h3>

<p> Components intended for HTML topic pages are very similar to generic lightweight

components. Components that do not require information about the View, or have

parameters that can be set, can be used without modification.

<h4>View Information</h4>

<p> Lightweight components that require information about the <code>View</code>

must implement <code>javax/javahelp/impl/ViewAwareComponent</code>. These components

implement the method <code>setViewData()</code>. The component can determine

information from the <code>View</code> about the environment in which it is

executing. For example, in the code snippet below the <code>Document</code>

object is derived from the <code>View</code>:

<pre> private View myView;

static private URL base;

public void setViewData(View v) {

myView = v;

Document d = myView.getDocument();

// System.err.println("myDocument is: "+d);

base = ((HTMLDocument) d).getBase();

// System.err.println(" base is: "+base);

}</pre>

For more information about the <code>Document</code> interface see the following

Swing API:

<pre>    http://java.sun.com/j2se/1.4.1/docs/api/javax/swing/text/Document.html</pre>

Text formatting information can be derived from the <code>View</code> by querying

its attribute set. Use the method <code>getAttributes</code> as shown below:

<pre>    AttributeSet as = v.getAttributes();</pre>

Format attributes can be used by the component when the <code>AttributeSet</code>

is passed as a parameter to a <code>StyleConstants</code> method. There are methods

that can be used to determine a number of attributes, including the font family,

font size, font weight, font style, underlining, background color, and foreground

color. For example, to determine the default background color of an object, you

can do the following:

<pre>    Color color=StyleContants.getBackground(as)</pre>

For a full list of formatting attributes and corresponding methods see:

<pre>    http://java.sun.com/j2se/1.4.1/docs/api/javax/swing/text/StyleConstants.html</pre>

<h4>Using Parameters</h4>

<p>

If your component takes parameters, you should follow these

two additional steps:

<ol>

<li>Add accessor methods for each parameter that can be set.

<li>Create a <code>BeanInfo</code> class that corresponds to the lightweight

component class.

</ol>

<img src="../../images/hg_note.gif" width="18" height="13"> The component

must accept parameter elements in any order.

<h4>Accessor Methods</h4>

<p> Add accessor methods that enable the component to access the parameters through

the Java reflection mechanism. In the following example, the <code>AButton</code>

class has implemented accessor methods for the parameter "data" in the methods

<code>getData</code> and <code>setData</code>:

<pre> private String data = "";

public void setData(String s) {

data = s;

}

public String getData() {

return data;

}</pre>

</td>

<td width="98%">Even if the internal representation is not a <code>String</code>,

both the returned value for the getter method and the parameter in the setter

method must be a <code>String</code>. </td>

</tr>

</table>

<h4>BeanInfo Class</h4>

<p> Create a <code>BeanInfo</code> class that provides explicit information about

the lightweight component. The only method used by the <code>ContentViewer</code>

from the <code>BeanInfo</code> classes is <code>getPropertyDescriptors</code>.

In the complete example below, <code>JHSecondaryViewerBeanInfo</code> defines

the property data accessible through the <code>getData()</code> and <code>setData()</code>

methods in <code>JHSecondaryViewer</code>: <br>

<pre>public class JHSecondaryViewerBeanInfo extends SimpleBeanInfo {

public JHSecondaryViewerBeanInfo() {

}

public PropertyDescriptor[] getPropertyDescriptors() {

PropertyDescriptor back[] = new PropertyDescriptor[15];

try {

back[0] = new PropertyDescriptor("content", JHSecondaryViewer.class);

back[1] = new PropertyDescriptor("id", JHSecondaryViewer.class);

back[2] = new PropertyDescriptor("viewerName", JHSecondaryViewer.class);

back[3] = new PropertyDescriptor("viewerActivator", JHSecondaryViewer.class);

back[4] = new PropertyDescriptor("viewerStyle", JHSecondaryViewer.class);

back[5] = new PropertyDescriptor("viewerLocation", JHSecondaryViewer.class);

back[6] = new PropertyDescriptor("viewerSize", JHSecondaryViewer.class);

back[7] = new PropertyDescriptor("iconByName", JHSecondaryViewer.class);

back[8] = new PropertyDescriptor("iconByID", JHSecondaryViewer.class);

back[9] = new PropertyDescriptor("text", JHSecondaryViewer.class);

back[10] = new PropertyDescriptor("textFontFamily", JHSecondaryViewer.class);

back[11] = new PropertyDescriptor("textFontSize", JHSecondaryViewer.class);

back[12] = new PropertyDescriptor("textFontWeight", JHSecondaryViewer.class);

back[13] = new PropertyDescriptor("textFontStyle", JHSecondaryViewer.class);

back[14] = new PropertyDescriptor("textColor", JHSecondaryViewer.class);

return back;

} catch (Exception ex) {

return null;

}

}</pre>

<h4>Parameter Names</h4>

<p> When naming parameters, be sure to avoid names reserved in the HTML 4.0 specification

for use as <code><OBJECT></code> tag attributes. For a complete list of

<code><OBJECT> </code>attributes see the HTML 4.0 specification:

<h3>Using the <code><OBJECT></code> Tag</h3>

<p> You add lightweight components to JavaHelp topics by means of the <code><OBJECT></code>

tag and its <code>classid</code> attribute. The help viewer only recognizes

<code>classid</code> values prefixed with the "<code>java:</code>" tag. All

other <code>classid</code> tags are ignored. The following example creates an

<code>ALabel</code> within the HTML topic:

You can use standard <code><OBJECT></code> tag attributes (see the HTML

4.0 specification for more details), but to be recognized the lightweight component

must have getter and setter methods for those attributes. A getter or setter

method must operate on a <code>String</code>. For example, in the following example

width and height for the <code>ALabel</code> are set if there are <code>getWidth</code>/<code>setWidth</code>

and <code>getHeight</code>/<code>setHeight</code> methods in <code>ALabel</code>:

<pre> <OBJECT

CLASSID="java:sunw.demo.object.ALabel"

width="400" height="500">

</OBJECT></pre>

<p> Parameters are passed to lightweight components by using the <code><param></code>

tag. A parameter is only recognized if the component has getter and setter

methods for that parameter. A getter or setter method must operate on a

<code>String</code>. In the example below, the help viewer passes a number of

parameters and their values to a the <code>JHSecondaryViewer</code> component:

<br>

</OBJECT></pre>

<h3>Supplemental Information</h3>

<p> The following information supplements the information in this topic.

<p>

<b>Lightweight Java Components</b>

<p>

For general information about lightweight Java components see:

<pre><a href="http://java.sun.com/j2se/1.4.1/docs/guide/awt/demos/lightweight/index.html">http://java.sun.com/j2se/1.4.1/docs/guide/awt/demos/lightweight/index.html</a></pre>

<b>JavaHelp Components</b>

<p>

As a reference, the sources to the lightweight components

that implement JavaHelp system popups and secondary windows

(<code>JHSecondaryViewer.java</code> and

<code>JHSecondaryViewerBeanInfo.java</code>) can be found in

<code>src.jar</code> at:

<pre>com\sun\java\javahelp\impl</pre>

For a description of how the <code><OBJECT></code> tag is used to implement

popups and secondary windows, see <a href="popup.html">Using Popup and Secondary

Windows</a>.

<p>

<b>HTML 4.0 Specification</b>

<p>

You can find a detailed description of the

<code><OBJECT></code> tag as part of the HTML 4.0

specification:

</body>

</html>

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