Additional Use for Parentheses.

[Eden Landau]

Hello! I came across this bit of code the other day.
Can anyone tell me what role do the oddly placed parentheses in line 67 play?
Thank you all very much!

package zetcode;

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.border.EtchedBorder;

public class MultipleSources extends JFrame {

    JLabel statusbar;

    public MultipleSources() {

        initUI();
    }

    public final void initUI() {

        JPanel panel = new JPanel();
        statusbar = new JLabel(" ZetCode");

        statusbar.setBorder(BorderFactory.createEtchedBorder(
                EtchedBorder.RAISED));

        panel.setLayout(null);

        JButton close = new JButton("Close");
        close.setBounds(40, 30, 80, 25);
        close.addActionListener(new ButtonListener());

        JButton open = new JButton("Open");
        open.setBounds(40, 80, 80, 25);
        open.addActionListener(new ButtonListener());

        JButton find = new JButton("Find");
        find.setBounds(40, 130, 80, 25);
        find.addActionListener(new ButtonListener());

        JButton save = new JButton("Save");
        save.setBounds(40, 180, 80, 25);
        save.addActionListener(new ButtonListener());

        panel.add(close);
        panel.add(open);
        panel.add(find);
        panel.add(save);

        add(panel);
        add(statusbar, BorderLayout.SOUTH);

        setTitle("Multiple Sources");
        setSize(400, 300);
        setLocationRelativeTo(null);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
    }

    class ButtonListener implements ActionListener {

        public void actionPerformed(ActionEvent e) {
            JButton o = (JButton) e.getSource();
            String label = o.getText();
            statusbar.setText(" " + label + " button clicked");
        }
    }

    public static void main(String[] args) {

        SwingUtilities.invokeLater(new Runnable() {

            public void run() {
                MultipleSources ms = new MultipleSources();
                ms.setVisible(true);
            }
        });
    }
}

[Jesper de Jong]

Do you mean this line?

JButton o = (JButton) e.getSource();

The (JButton) is a type cast. It means that the compiler should treat whatever object e.getSource() returns as if it is a JButton object.

There's some information about type casting on this page from Oracle's Java Tutorials.

[Eden Landau]

That solves it then! Thank you very much!