CODEWITHSUNDEEP
javakeyevent
Dipto_Das
Dipto_Das

Reputation: 53

If KEY_TYPED event occurs when a character is generated, then why does code parameter to KeyEvent contains VK_UNDEFINED?

I am taking help from Java:The complete reference(8th Ed) by Herbert Schildt to learn about Java. While reading, I found that KEY_TYPED event occurs only when a character is generated. Doesn't that mean that a character (0-9,A-Z) is generated? If so, then shouldn't the corresponding ASCII equivalents be passed as code to the KeyEvent constructor:

KeyEvent(Component src, int type, long when, int modifiers, int code, char ch)

But the book says, for KEY_TYPED events, code will contain VK_UNDEFINED. Isn't code here defined with the key typed?

Upvotes: 2

Views: 156

Answers (1)

ElderBug
ElderBug

Reputation: 6145

This is because a KEY_TYPED event doesn't necessarily have a corresponding VK code. VK codes comes from the keyboard, and represent a key. If I press the 'a' key, I will see a key press event with VK_A code. Now, KEY_TYPED events, as you said, occur when a character is generated. The thing is, character are generated by the OS after translating VK codes through a character map that depends on the locale.

As an example, with my keyboard I can type an 'ö' with a certain combination of keys. This will fire a bunch of key events with VK_SHIFT, VK_DEAD_CIRCUMFLEX and VK_O, but only one KEY_TYPED event, with the 'ö' character. Worse, I can type a '†' by pressing 6 keys (ALT+0+1+4+1+4), yet again, only one KEY_TYPED event will be fired. Now, what VK code would you put in the event ? That doesn't really mean anything, so they decided to always put VK_UNDEFINED to stay consistent, even with simple characters.

Upvotes: 4

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