■ソースコード

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class samplewindows {
    /**
    * @param args
    */
    public static void main(String[] args) {
        // TODO 自動生成されたメソッド・スタブ
        JFrame frame = new JFrame("リスト表示");
        AddListPanel panel1 = new AddListPanel();
        Container cont = frame.getContentPane();
        cont.add(panel1);
        //set up frame
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setBounds(0, 0, 300, 500);
        frame.setVisible(true);
    }
}
class AddListPanel extends JPanel implements ActionListener{
    private final long serialVersionUID = 1L;
    JButton button1, button2;
    JList list1;
    JTextField text1;
    DefaultListModel listModel;
    JLabel label1;
    AddListPanel(){
        button1 = new JButton("選択");
        button1.addActionListener(this);
        listModel = new DefaultListModel();
        listModel.addElement("りんご");
        list1 = new JList(listModel);
        list1.setFixedCellWidth(100);
        button2 = new JButton("追加");
        button2.addActionListener(this);
        JScrollPane scroll1 = new JScrollPane(list1);
        scroll1.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        scroll1.setPreferredSize(new Dimension(240, 100));
        scroll1.setBorder(BorderFactory.createEtchedBorder());
        scroll1.setBorder(BorderFactory.createTitledBorder("果物"));
        text1 = new JTextField(12);
        label1 = new JLabel("ここに新しい項目を入力してください");
        JPanel p1  = new JPanel();
        p1.add(scroll1);
        p1.add(button1);
        JPanel p2 = new JPanel();
        p2.setLayout(new GridLayout(2, 1));
        p2.add(label1);
        p2.add(text1);
        JPanel p3 = new JPanel();
        p3.add(button2);
        this.setLayout(new GridLayout(3, 1));
        this.add(p1);
        this.add(p2);
        this.add(p3);
    }
    public void actionPerformed(ActionEvent el){
        if(el.getSource() == button1){
            JOptionPane.showMessageDialog(
                null,
                list1.getSelectedValue() + "が選択されました",
                "選択項目の表示",
                JOptionPane.INFORMATION_MESSAGE
            );
        }
        else if(el.getSource() == button2){
            if(text1.getText().compareTo("") != 0){
                listModel.addElement(text1.getText());
            }
            else{
                JOptionPane.showMessageDialog(
                    null,
                    "設定する項目が入力されていません",
                    "入力エラー",
                    JOptionPane.INFORMATION_MESSAGE
                );
            }
        }
    }
}

病み上がりだし、夜も遅いしで解説はマタ明日。。。