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<h1>The AWT Modality</h1>
<p>
This document, together with the API documentation for modality-related
classes (such as <code>java.awt.Dialog</code>), briefly describes the new
modality features and how to use them. It contains the following sections:
</p><ul>
<li><a href="#Definitions">Definitions</a></li>
<li><a href="#ModalityTypes">Modality types</a></li>
<li><a href="#ShowHideBlocking">Show/hide blocking</a></li>
<li><a href="#ModalExclusion">Modal exclusion</a></li>
<li><a href="#Related">Related AWT features</a></li>
<li><a href="#Security">Security</a></li>
<li><a href="#PlatformSupport">Platform support</a></li>
<li><a href="#Compatibility">Compatibility</a></li>
<li><a href="#Examples">Examples</a></li>
</ul>
<a id="Definitions"></a>
<h2>Definitions</h2>
<p>
Document - a window without an owner that, together with
all its child hierarchy, may be operated on as a single self-contained
document.
Every window belongs to some document — its root can be found as
the closest ancestor window without an owner.
</p><p>
<a id="ModalBlocked"></a>
Modal blocked window - a window, that:
</p><ul>
<li>doesn't receive any user input events
</li><li>doesn't receive input focus
</li><li>keeps its Z-order below the modal dialog that blocks it
</li></ul>
<blockquote>
<hr>
<b>Warning!</b> Some window managers allow users to change the window
Z-order in an arbitrary way — in that case the last requirement
may not be met.
<hr>
</blockquote>
<p>
Modal dialog - a dialog that blocks some windows while it is
visible. The blocked windows are determined according to the dialog's
scope of blocking.
</p><p>
Modal excluded window - a window that stays unblocked
while the modal dialog is visible. If a window is modal excluded
then all its owned windows and child components are also excluded.
</p><p>
Scope of blocking (SB) - the set of windows (instances of
<code>java.awt.Window</code> and all derived classes) that are blocked by
the modal dialog while it is visible.
<blockquote><hr>
<b>Note</b>: Everywhere in this document the notion of "window" is equal
to a top-level window in the Java programming language — in other words
an instance of <code>java.awt.Window</code> or any descendant class.
<hr></blockquote>
<a id="ModalityTypes"></a>
<h2>Modality types</h2>
<p>
There are four supported modality types :
</p><ul>
<li>toolkit
</li><li>application
</li><li>document
</li><li>modeless
</li></ul>
A dialog is, by default, modeless. A modal dialog is, by default,
application-modal.
<ol>
<li>Modeless dialogs<br>
A modeless dialog doesn't block any windows while visible.
</li><li>Document-modal dialogs<br>
A document-modal dialog blocks all windows from the same
document except those from its child hierarchy. The document root
is determined as the closest ancestor window without an
owner.
</li><li>Application-modal dialogs<br>
An application-modal dialog blocks all windows from the same
application except for those from its child hierarchy.
If there are several applets launched in a browser, they can be
treated either as separate applications or a single application.
This behavior is implementation-dependent.
</li><li>Toolkit-modal dialogs<br>
A toolkit-modal dialog blocks all windows that run in the same
toolkit except those from its child hierarchy. If there
are several applets launched all of them run with the same toolkit,
so a toolkit-modal dialog shown from an applet may affect other
applets and all windows of the browser instance which embeds the
Java runtime environment for this toolkit.
See the security section below.
</li></ol>
<p>
Modality priority is arranged by the strength of blocking: modeless,
document-modal, application-modal and toolkit-modal. This arrangement
is used when determining what dialog should remain unblocked if two
are visible and block each other. It naturally reflects the nesting
of a dialog's scope of blocking (SB): a modeless dialog has an empty SB,
a document-modal dialog's SB is complete in some applications,
and all the applications are run in one toolkit. </p><p>
Notes about owners:
</p><ul>
<li>Creating a document-modal dialog without an owner:<br>
Since <code>Dialog</code> is a class derived from
<code>Window</code>, a <code>Dialog</code> instance automatically
becomes the root of the document if it has no owner. Thus, if
such a dialog is document-modal, its scope of blocking is empty
and it behaves the same way as a modeless dialog.
</li><li>Creating an application-modal or toolkit-modal dialog with an
owner:<br>
The scope of blocking for an application- or toolkit-modal
dialog, as opposed to a document-modal dialog, doesn't depend on
its owner. Thus, in this case the only thing that the owner
affects is the Z-order: the dialog always stays on top of its owner.
</li></ul>
<blockquote><hr>
<b>Implementation note</b>: Changing the modality type for a visible
dialog may have no effect until it is hidden and then shown again.
<hr></blockquote>
<a id="ShowHideBlocking"></a>
<h2>Show/hide blocking</h2>
<p>
Showing the window or modeless dialog: "F"<br>
All the visible modal dialogs are looked through — if F is from the SB
of one of them, it becomes blocked by it. If there are several such
dialogs, the first shown is used. If no such dialogs exist, F remains
unblocked.
</p><p>
Showing the modal dialog: "M"<br>
When modal dialog M is shown, all the visible windows fall into one of
three distinct groups:
<ul>
<li>Blockers of M (modal dialogs that block M and
either are in M's child hierarchy, or are not blocked by M, or have
a greater mode of modality, or block some other blocker of M)
<li>Blocked by M (windows from M's SB that are not blockers and are
not in child hierarchy of any blocker)
<li>All other windows (windows or modeless
dialogs outside M's SB and modal dialogs outside M's SB that do not
block M).
</ul>
<p>
After the modal dialog M is shown, it becomes blocked by the first shown
dialog from the first group (if there are any), all the windows from the
second one become blocked by M, and all the windows from the third group
remain untouched.
</p><p>
In typical cases, when no child dialogs are shown before their owners,
this rule can be simplified. (The following, simplified case, may
leave out some details).
</p><p>
Showing the document-modal dialog: "M"<br>
All the visible application- and toolkit-modal dialogs are looked
through — if M is from the SB of one of them,
it becomes blocked by it. If there are several such dialogs,
the first shown is used. If no such dialogs exist, M remains unblocked.
</p><p>
Showing the application-modal dialog: "M"<br>
All the visible toolkit-modal dialogs are looked through —
if M is from the SB of one of them, it becomes blocked by it.
If there are several such dialogs, the first shown is used.
If no such dialogs exist, M remains unblocked.
</p><p>
Showing the toolkit-modal dialog: "M"<br>
M remains unblocked.
<table border="1">
<caption>The Standard Blocking Matrix</caption>
<tbody><tr>
<th scope="col">current/shown</th>
<th scope="col">frame & modeless</th>
<th scope="col">document</th>
<th scope="col">application</th>
<th scope="col">toolkit</th>
</tr>
<tr>
<th scope="row">-</th>
<td>-</td>
<td>-</td>
<td>-</td>
<td>-</td>
</tr>
<tr>
<th scope="row">document</th>
<td>blocked</td>
<td>-</td>
<td>-</td>
<td>-</td>
</tr>
<tr>
<th scope="row">application</th>
<td>blocked</td>
<td>blocked</td>
<td>-</td>
<td>-</td>
</tr>
<tr>
<th scope="row">toolkit</th>
<td>blocked</td>
<td>blocked</td>
<td>blocked</td>
<td>-</td>
</tr>
</tbody>
</table>
<p>
After the modal dialog is shown, all the windows from its SB are blocked,
except those that block this modal dialog.
</p><p>
Hiding the window or modeless dialog: "F"<br>
If F was blocked by any modal dialog M, it becomes unblocked and is
removed from M's blocked windows list.
</p><p>
Hiding the modal dialog: "M"<br>
If M was blocked by any other modal dialog, for example, "N",
it becomes unblocked and
is removed from N's blocked windows list. Then, all the windows and dialogs
blocked by M become unblocked, and after that the same checks
(as in Showing the modal dialog: "M")
are performed for each of them in the order they were initially shown.
<a id="ModalExclusion"></a>
</p><h2>Modal exclusion</h2>
<p>
There are two modal exclusion types introduced as of JDK 6
</p><ul>
<li>Exclusion from blocking of toolkit-modal dialogs
</li><li>Exclusion from blocking of application-modal dialogs
</li></ul>
By default, a window's modal exclusion property is turned off.
<ol>
<li>Application-modal exclusion<br>
If a window is application-modal excluded, it is not blocked by any
application-modal dialogs. Also, it is not blocked by document-modal
dialogs from outside of its child hierarchy.
</li><li>Toolkit-modal exclusion<br>
If a window is toolkit-modal excluded, it is not blocked
by any application- or toolkit-modal dialogs. Also, it is not
blocked by document-modal dialogs from outside of their child hierarchy.
</li></ol>
<blockquote>
<hr>
<b>Implementation note</b>: Changing the modal exclusion type for a visible window
may have no effect until it is hidden and then shown again.<hr>
</blockquote>
<a id="Related"></a>
<h2>Related AWT features</h2>
<p>
Always-On-Top<br>
When a modal dialog that is not always-on-top blocks an always-on-top window,
their relative Z-order is unspecified and platform-dependent.
</p>
<p>
The <code>toFront()</code> and <code>toBack()</code> methods<br>
A modal dialog should always be above all its blocked windows. Thus, if a blocked
window is brought to the front, its blocking dialog, if any, is also brought to the
front and remains above the blocked window. Likewise, if a modal dialog is sent to
the back, all of its blocked windows are sent to the back to keep them below the
blocking dialog.
</p>
<p>
Minimizing, maximizing and closing blocked windows<br>
When a modal dialog blocks a window, the user may not be able to maximize or
minimize the blocked window— however, the actual behavior is unspecified
and platform-dependent. In any case, the user can't close the blocked window
interactively— but it can be closed programmatically by calling the
<code>setVisible(false)</code> or <code>dispose()</code> methods on the blocked
window.
</p>
<p>
Blocked windows activations<br>
When the user selects a blocked window, it may be brought to the front, along
with the blocking modal dialog which would then become the active window—
however, the actual behavior is unspecified and platform-dependent.
</p>
<p>
Hiding a modal dialog<br>
When the modal dialog that currently has focus is hidden, it is unspecified
and platform-dependent, which other window will become the active window.
Any of the following may become the active window:
<ol>
<li>The owner of the modal dialog - if the owner is unblocked.
</li><li>The <code>Window</code>, which was active before this modal dialog gained
focus - if the owner of the modal dialog is absent or is blocked.
</li></ol>
If the modal dialog to be hidden does not have focus, the active window remains
unchanged.
<a id="Security"></a>
<h2>Security</h2>
<p>
A special <code>AWTPermission</code>, <code>"toolkitModality"</code>,
is required to show toolkit-modal
dialogs. This would prevent, for example, blocking a browser or
Java Web Start (JWS) by modal dialogs shown from applets.
</p><p>
The same permission is required to exclude a window from toolkit modality.
This would prevent, for example, a dialog shown from an applet not to be
blocked by a browser's or JWS's modal dialog.
<a id="PlatformSupport"></a>
</p><h2>Platform support</h2>
<p>
Two <code>java.awt.Toolkit</code> methods allow you to check whether
the current platform supports specific modality features:
</p><ul>
<li><code>isModalityTypeSupported(modalityType)</code><br>
Returns whether the specified modality type is supported on
the current platform.
If mode "M" is not supported and a dialog is set to M-modal,
it behaves as modeless.
</li>
<li><code>isModalExclusionTypeSupported(modalExclusionType)</code><br>
Returns whether the given modal exclusion type is supported on
the current platform. If exclusion type "E" is not supported
and a window is marked as E-excluded, this has no effect.
</li></ul>
<a id="Compatibility"></a>
<h2>Compatibility</h2>
<p>
The default modality type is application-modal. It is used by the API
calls: <code>Dialog.setModal(true)</code>,
<code>Dialog(owner, true)</code>, etc. Prior to JDK 6
the default type was toolkit-modal,
but the only distinction between application- and toolkit-modality is for
applets and applications launched from Java Web Start.
<a id="Examples"></a>
</p><h2>Examples</h2>
<h3>Example 1</h3>
<ol style="float: left">
<li>Frame F is shown<br>
<li>Document-modal dialog D<sub>i</sub> is shown<br>
<li>F becomes blocked by D<sub>i</sub> — it's in the same document<br>
<li>Document-modal dialog D<sub>ii</sub> is shown<br>
<li>D<sub>i</sub> becomes blocked by D<sub>ii</sub> — it's in the
same document<br>
</ol>
<p style="float: left; margin-left: 1em">
<img src="modal-example1.gif" alt="Example 1">
</p>
<h3 style="clear: left">Example 2</h3>
<ol style="float: left">
<li>Frame F is shown<br>
<li>Document-modal dialog D<sub>i</sub> is shown<br>
<li>F becomes blocked by D<sub>i</sub> — it's in the same document<br>
<li>Document-modal dialog D<sub>ii</sub> is shown<br>
<li>D<sub>i</sub> becomes blocked by D<sub>ii</sub> — it's in the
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