Java – Setting up application wide Key Listeners

javakeyboard shortcutsswing

How do i setup application wide key listeners (keyboard shortcuts), so that when a key combination (e.g. Ctrl + Shift + T) is pressed, a certain action is invoked in a Java application.

I know keyboard shortcuts can be set JMenuBar menu items, but in my case the application does not have a menu bar.

Best Answer

Check out the How To Use Key Bindings section of the Java tutorial.

You need to create and register an Action with your component's ActionMap and the register a (KeyStroke, Action Name) pair in one of your application's component's InputMaps. Given that you don't have a JMenuBar you could simply register the key bindings with a top-level JPanel in your application.

For example:

Action action = new AbstractAction("Do It") { ... };

// This is the component we will register the keyboard shortcut with.
JPanel pnl = new JPanel();

// Create KeyStroke that will be used to invoke the action.
KeyStroke keyStroke = KeyStroke.getKeyStroke(KeyEvent.VK_T, InputEvent.CTRL_DOWN_MASK | InputEvent.SHIFT_DOWN_MASK);

// Register Action in component's ActionMap.
pnl.getActionMap().put("Do It", action);

// Now register KeyStroke used to fire the action.  I am registering this with the
// InputMap used when the component's parent window has focus.
pnl.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW).put(keyStroke, "Do It");

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Java – Sort a Map by values

Here's a generic-friendly version:

public class MapUtil {
    public static <K, V extends Comparable<? super V>> Map<K, V> sortByValue(Map<K, V> map) {
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        list.sort(Entry.comparingByValue());

        Map<K, V> result = new LinkedHashMap<>();
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.net – How to create compound keyboard shortcuts in a Windows Forms application

In answer to the question of keyboard chords specifically, I do not believe there is a ready-made option available to you at this point.

However, it should be simple enough to model. I would create a single class, perhaps KeyboardChordProvider. It will need to know about keyboard events at the form level. As stated elsewhere, the Form.KeyPreview property must be true. It may be enough for this provider to subscribe to the Form.KeyPress event. You could do all of this in the provider's constructor if you passed in the form.

You would need to register the potential keystrokes with the provider.

Internally this instance will track the current state. Whenever a keystroke is observed that represents the first key of the chord, you would update the provider's state and raise an event so that a subscriber could set text: (CTRL+W) was pressed. Waiting for second key of chord...

If the next keystroke matches a potential secondary option, then you have a match and could raise a ChordPressed event containing the details of the strokes entered. Alternatively, you might just call a particular callback that was given to the provider at the time the chord was registered (to avoid having a switch statement or some other dispatch in the ChordPressed event handler).

If, at any time, a keystroke does not match a potential next option, then you would reset the state of the provider.

Internal to the provider you might model the possible keystrokes using a tree structure. The current state of the provider is just a particular tree node. At the beginning, the root node would be active. If a child matches a keystroke then it becomes the current node in anticipation of the next stroke. If the child was a leaf node, then an entire chord has matched and you would raise ChordPressed event (passing the chain of strokes that got you to that point) or invoke the callback stored in the leaf. Whenever no keystroke matches a child, reset back to making the root node active.

I think this design would achieve what you want.

Best Answer

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.net – How to create compound keyboard shortcuts in a Windows Forms application

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