This reference is for Processing 3.0+. If you have a previous version, use the reference included with your software in the Help menu. If you see any errors or have suggestions, please let us know. If you prefer a more technical reference, visit the Processing Core Javadoc and Libraries Javadoc.



// Click on the image to give it focus,
// and then press any key.

int value = 0;

void draw() {
  rect(25, 25, 50, 50);

void keyPressed() {
  if (value == 0) {
    value = 255;
  } else {
    value = 0;
Description The keyPressed() function is called once every time a key is pressed. The key that was pressed is stored in the key variable.

For non-ASCII keys, use the keyCode variable. The keys included in the ASCII specification (BACKSPACE, TAB, ENTER, RETURN, ESC, and DELETE) do not require checking to see if the key is coded; for those keys, you should simply use the key variable directly (and not keyCode). If you're making cross-platform projects, note that the ENTER key is commonly used on PCs and Unix, while the RETURN key is used on Macs. Make sure your program will work on all platforms by checking for both ENTER and RETURN.

Because of how operating systems handle key repeats, holding down a key may cause multiple calls to keyPressed(). The rate of repeat is set by the operating system, and may be configured differently on each computer.

Note that there is a similarly named boolean variable called keyPressed. See its reference page for more information.

Mouse and keyboard events only work when a program has draw(). Without draw(), the code is only run once and then stops listening for events.
Updated on January 15, 2016 00:43:38pm EST

Creative Commons License