[Java] 20150924_Swing

/***************************************/
/** 20150924 Swing                    **/
/** Maker  : Yan                      **/
/** E-Mail : [email protected] **/
/** Date   : 2015/09/24 am.11:30      **/
/***************************************/

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Source {

    public static void main(String[] args) {
        JFrame demo = new JFrame();
        demo.setSize(400, 300);
        demo.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        demo.getContentPane().setLayout(new FlowLayout());

        // Add Combobox
        JComboBox combo = new JComboBox();
        combo.addItem("50");
        combo.addItem("100");
        combo.addItem("150");
        combo.addItem("200");
        demo.getContentPane().add(BorderLayout.SOUTH, combo);

        // Add Button
        JButton button = new JButton("Sum");
        demo.getContentPane().add(BorderLayout.SOUTH, button);

        // Add Label
        JLabel label = new JLabel("-------------");
        demo.getContentPane().add(BorderLayout.SOUTH, label);


        button.addActionListener(new buttonHandler(label, combo));
        demo.setVisible(true);
    }
}

class buttonHandler implements ActionListener{
    private JLabel label;
    private JComboBox combo;
    public buttonHandler(JLabel label, JComboBox combo) {
        this.label = label;
        this.combo = combo;
    }
    @Override
    public void actionPerformed(ActionEvent e) {
        // TODO Auto-generated method stub
        int sum = 0;
        for (int i = 1; i <= Integer.parseInt(String.valueOf(combo.getSelectedItem())); i++) {
            sum += i;
        }
        label.setText("Sum(1-" + String.valueOf(combo.getSelectedItem()) + ") = " + sum);
    }
}