b.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e){
            //do some stuff
        }
    });

btn.addMouseListener(new MouseListener() {

    @Override
    public void mousePressed(MouseEvent e) {
        //do some stuff
    }

    /*Override other methods*/

});

btn.addMouseListener(new MouseAdapter() {

        @Override
        public void mousePressed(MouseEvent e) {
            //do some stuff
        }

        /*No need to override other methods, `MouseAdapter` already does it*/

    });

b.addMouseListener(new MouseListener() {

    public void mouseClicked(MouseEvent e) {}
    public void mouseEntered(MouseEvent e) {}
    public void mouseExited(MouseEvent e) {}
    public void mousePressed(MouseEvent e) {
        doOnPressedAction();
    }
    public void mouseReleased(MouseEvent e) {
        doOnReleasedAction();
    }
});
b.addKeyListener(new KeyListener(){
    public void keyTyped(KeyEvent e) {}

    public void keyPressed(KeyEvent e) {
        if (sendButton.getModel().isPressed()) {
            doOnPressedAction();
        } else {
            // just in case it can happen that the button is released on
            // a key press action (maybe another controls key listener...)
            doOnReleasedAction();
        }
    }

    public void keyReleased(KeyEvent e) {
        doOnReleasedAction();
    }
});