General > Keys
preference page. Within Eclipse, key strokes and key sequences are assigned to invoke particular commands.The function of the keyboard can be extensively customized in Eclipse using the
General > Keys
preference page. Within Eclipse, key strokes and key sequences are assigned to invoke particular commands.
A 'key stroke' is the pressing of a key on the keyboard, while optionally holding down one or more of these
modifier keys: Ctrl, Alt (⌥ on macOS), Shift, or ⌘
(only on macOS.) For example, holding down Ctrl then pressing A produces the key stroke
Ctrl+A. The pressing of the modifier keys themselves do not constitute key strokes.
A 'key sequence' is one or more key strokes. Traditionally, Emacs assigned two or three key stroke key sequences
to particular commands. For example, the normal key sequence assigned to Close All in emacs is
Ctrl+X Ctrl+C. To enter this key sequence, one presses the key stroke Ctrl+X followed by
the key stroke Ctrl+C. While Eclipse supports key sequences of arbitrary lengths, it is recommended that
keyboard shortcuts be four key strokes in length (or less).
A 'key binding' is the assignment of a key sequence to a command.
A 'scheme' is a set of bindings. Eclipse includes two schemes:
The Default scheme contains a general set of bindings, in many cases recognizable as traditional key
sequences for well known commands. For instance, Ctrl+A is assigned to Select All, and
Ctrl+S is assigned to Save.
The Emacs scheme contains a set of key bindings familiar to users of Emacs. For instance, Ctrl+X
H is assigned to Select All, and Ctrl+X S is assigned to Save.
The Emacs scheme is not a complete set of bindings like the Default scheme. Rather, it borrows
from the Default scheme where possible, only defining explicit Emacs-style bindings where they vary from the
Default scheme. Generally, only well known commands like Select All, Save, etc.
have specific Emacs key sequences associated with them.
Key bindings can vary based on the current context of Eclipse.
Sometimes the active part might be a Java file editor, for instance, where a different set of key sequence
assignments may be more appropriate than if the active part was an html file editor. As a specific example, typically
Ctrl+B is assigned to Build in a context such as Java file editing, while
Ctrl+B is assigned to Make Text Bold in a context such as HTML file editing. This context
is usually determined by the active part, but it can be influenced by the active window or dialog as well. If the
active part does not choose a particular context, the workbench will set the active context to In
Windows.
Eclipse includes a number of different contexts. Some examples are:
Contexts can extend other contexts. For example, the Editing Java Source context borrows key bindings from the Editing Text context, which in turn borrows key bindings from the In Windows context.
Note: It is not recommended to promote a key binding to a context which it extends. For example, it is not recommended to move an Editing Text key binding to the In Dialogs and Windows context. This may have unexpected results.
It is possible for some key bindings to work in dialogs. Those key bindings are assigned to the In Dialogs and Windows context. One example of such a key binding is the key binding for "cut". It is possible to change these key bindings. For example, it is possible to have Ctrl+X as cut in dialogs, but Ctrl+W as cut in windows.
Key bindings also vary by platform and locale. On the macOS platform, ⌘+S is assigned to
Save, instead of the usual Ctrl+S. On Chinese locales (zh), Alt+/ is assigned
to Content Assist, instead of the usual Ctrl+Space.
The current platform and locale is determined when Eclipse starts, and does not vary over the course of an Eclipse instance.
Key bindings are provided by plug-ins, and in Eclipse, plug-ins can be added or removed. This can cause key
bindings declared by these plug-ins to be added or removed. Consider CTRL+6 was assigned to the
About command in the Default scheme. Say you install a new plug-in that assigns
CTRL+6 to a particular command. Eclipse will preserve your assignment to About.
There are only a finite number of simple, common key strokes available to assign to a multitude of commands.
Scheme, context, platform, and locale all partition key sequence assignments into domains where they
don't conflict with one another. Consider the case for Ctrl+B key binding if contexts did not exist. One
plug-in would assign Ctrl+B to Build, the other plug-in would assign Ctrl+B to
Make Bold Text. How would Eclipse properly resolve this conflict?
Though conflicts are drastically reduced by employing the above mechanisms, they can still occur. Two plug-ins,
independent of one another, could assign the same key sequence to different commands with the same context, scheme,
platform, and locale. Consider if a plug-in assigned Ctrl+F4 in the In Windows context and
Default scheme to one of its commands. This directly conflicts with Eclipse assigning Ctrl+F4
to the close command in the same context and scheme.
This is a conflict. Eclipse pop up the Key Assist Dialog with the conflicting commands and allow the user to select one. The Key Assist dialog is the same dialog that displays command choices for multiple key stroke key bindings.
These types of conflicts can be resolved by explicitly assigning the key sequence to one of the commands, or remove it from the other.
Another type of conflict can be caused by multiple-key stroke key sequences. For example, in the Emacs
scheme, there are many multiple-key stroke key sequences beginning with the key stroke Ctrl+X.
Ctrl+X K is assigned to Close. Ctrl+X H is assigned to Select All.
As previously mentioned, the Emacs scheme borrows key bindings from the Default scheme. In the
default scheme, Ctrl+X is assigned to Cut. Though the Emacs scheme doesn't
explicitly redefine Ctrl+X, pressing Ctrl+X is required as part of many of its key
bindings. In the Emacs scheme, when one presses Ctrl+X, one is half way to entering one of many
possible assigned key sequences. One would not expect the Cut action to be invoked at this time.
For this type of conflict, the rule is that the Ctrl+X key sequence assigned to Cut
would be ignored. Otherwise, it would not be possible to complete many of the key bindings in the Emacs
configuration.