CODEWITHSUNDEEP
javaclassobject
Josh
Josh

Reputation: 12566

Java Question, From a C++ Programmer

I'm learning Java, and now that I'm over the packages hump, things are going smoothly. I can draw similarities between most things I'm learning with things I already know at least the concept of. But what on earth is going on with the following bit of code? Is it some form of constructor, or anonymous object?

Something obj = new Something()
{
  private static final int num = 3;

  public void meth()
  {
    // w/e
  }
};

Upvotes: 2

Views: 101

Answers (3)

corsiKa
corsiKa

Reputation: 82559

/**
 * Notice there's only one thing in this that isn't defined:
 * It still needs public abstract void triggerEvent();
 */
public abstract static class TopButton extends JPanel implements MouseListener {
        protected ButtonPanel parent;
        private String text;
        public TopButton(ButtonPanel bp, String text) { parent = bp; this.text = text; addMouseListener(this); }
        public void mouseClicked(MouseEvent e) { triggerEvent(); }
        public void mouseEntered(MouseEvent e) { }
        public void mouseExited(MouseEvent e) { }
        public void mousePressed(MouseEvent e) { }
        public void mouseReleased(MouseEvent e) { }
        public abstract void triggerEvent();
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            Color oldColor = g.getColor();
            Font oldFont = g.getFont();
                Font newFont = new Font(oldFont.getName(),oldFont.getStyle(),oldFont.getSize());
                g.setFont(newFont);
                g.setColor(Color.black);
                g.drawString(text, 20, 20);
            g.setFont(oldFont);
            g.setColor(oldColor);
        }
    }

Now, when I actually define my buttons, I do this. By providing the one line it needs, the only thing that makes it different from others. Now I could make a new file for each one, and define a new class for each one. This is much simpler.

private static void loadButtonPanelButtons() {
    /* This button should tell the parent to bring up the save screen */
    TopButton save = new TopButton(buttonPanel,"Save") {
        public void triggerEvent() { parent.triggerSave(); }
    };
    save.setBorder(LineBorder.createBlackLineBorder());
    buttonPanel.add(save);

    /* This button should tell the parent to bring up the load screen */
    TopButton load = new TopButton(buttonPanel,"Load") {
        public void triggerEvent() { parent.triggerLoad(); }
    };
    load.setBorder(LineBorder.createBlackLineBorder());
    buttonPanel.add(load);

    TopButton addTile = new TopButton(buttonPanel,"Add Tile") {
        public void triggerEvent() { parent.triggerAddTile(); }
    };
    addTile.setBorder(LineBorder.createBlackLineBorder());
    buttonPanel.add(addTile);

    TopButton saveTiles = new TopButton(buttonPanel,"Save Tiles") {
        public void triggerEvent() { parent.triggerStyleSave(); }
    };
    saveTiles.setBorder(LineBorder.createBlackLineBorder());
    buttonPanel.add(saveTiles);
}

Now, when I handle the buttons being pressed, remember back in the definition of TopButton... there was

    public void mouseClicked(MouseEvent e) { triggerEvent(); }

We know triggerEvent() eventually gets defined. We can define it on a per-button basis, and when the panel gets clicked, no matter what we defined triggerEvent() to be, it gets called.

Upvotes: 2

Pawel Veselov
Pawel Veselov

Reputation: 4225

Such construct creates an anonymous inner class of a class where this construct is executed, and derived from Something (not an inner class of Something).

The idea is to quickly provide implementations for abstract classes, interfaces, or override some functionality of a class.

(new Thread(){ public void run() { System.out.println("executed on another thread"); }}).start();

Upvotes: 1

Matt Ball
Matt Ball

Reputation: 359816

You got it - this creates an anonymous inner class of Something.

See also: Nested Classes (The Java Tutorial) and Anonymous Classes.

Upvotes: 6

Related Questions