boolean isButtonDown = false;

private void someFunction() {
    if (buttonValue == true && isButtonDown == false) {
        isButtonDown = true;

        // This code will only be run ONCE
        // right when the button is first pressed
    } else if (buttonValue == false && isButtonDown == true) {
        isButtonDown = false

        // This code will be run ONCE
        // right when the button is first released
    } else if (buttonValue == true && isButtonDown == true) {
        // This code will be run CONTINUOUSLY
        // While the button is being held down

        // Don't put any code you want to run more than once here
    } else if (buttonValue == false && isButtonDown == false) {
        // This code will be run CONTINUOUSLY
        // While the button is NOT being held down

        // Don't put any code you want to run more than once here
    }
}