This document, together with the API documentation for modality-related
classes (such as
java.awt.Dialog), briefly describes the new
modality features and how to use them. It contains the following sections:
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.
Modal blocked window - a window, that:
Warning! 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.
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.
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.
Scope of blocking (SB) - the set of windows (instances of
java.awt.Window and all derived classes) that are blocked by
the modal dialog while it is visible.
Note: 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
java.awt.Windowor any descendant class.
There are four supported modality types :
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.
Notes about owners:
Dialogis a class derived from
Dialoginstance 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.
Implementation note: Changing the modality type for a visible dialog may have no effect until it is hidden and then shown again.
Showing the window or modeless dialog: "F"
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.
Showing the modal dialog: "M"
When modal dialog M is shown, all the visible windows fall into one of three distinct groups:
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.
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).
Showing the document-modal dialog: "M"
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.
Showing the application-modal dialog: "M"
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.
Showing the toolkit-modal dialog: "M"
M remains unblocked.
|current/shown||frame & modeless||document||application||toolkit|
After the modal dialog is shown, all the windows from its SB are blocked, except those that block this modal dialog.
Hiding the window or modeless dialog: "F"
If F was blocked by any modal dialog M, it becomes unblocked and is removed from M's blocked windows list.
Hiding the modal dialog: "M"
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.
There are two modal exclusion types introduced as of JDK 6
Implementation note: Changing the modal exclusion type for a visible window may have no effect until it is hidden and then shown again.
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.
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.
Minimizing, maximizing and closing blocked windows
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
dispose() methods on the blocked
Blocked windows activations
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.
Hiding a modal dialog
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:
Window, which was active before this modal dialog gained focus - if the owner of the modal dialog is absent or is blocked.
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.
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.
java.awt.Toolkit methods allow you to check whether
the current platform supports specific modality features:
The default modality type is application-modal. It is used by the API
Dialog(owner, true), 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.