How come a "pre-defined" function cant be put inside of a class?

edited July 2015 in How To...

I tried putting void mousePressed inside of a class and it wouldn't work, but then when I moved it outside of the class it worked. How come it only worked when outside of the class?


  • edited July 2015

    mousePressed() is a Processing PApplet's callback function. Just like setup() & draw() are too.
    If we place any of them inside another class, the PApplet class won't be able to find them!
    Unless we registerMethod() them btW: :P

  • edited July 2015

    Place mousePressed() in the global scope and have it call your class' method

    Here is an example:

    Foo[] foo;
    int counter = 0;
    void setup() {
      size(100, 100);
      foo = new Foo[3];
      for (int i = 0; i < 3; i++)
        foo[i] = new Foo(i);
    void draw() {
    void mousePressed() {
      counter = (counter + 1) % 3;
    class Foo {
      int index;
      Foo(int index) {
        this.index = index;
      void sayHello() {
        println("Hello from: " + index);
  • edited July 2015

    mousePressed is a build-in function that can obly be seen by processing when it's outside the classes. So when it's on a global level.

    As been said you can call the hidden mousePressed (it can have any name) that's inside the class from the real in-build mousePressed (outside the class):

    void mousePressed(){ 

    Same goes for mouseClicked etc etc

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