java.util.Regex（正規表現）

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JTextField;

public class FirstProject extends JFrame implements ActionListener{

    JFrame frame = null;
    JTextField text = null;
    JLabel label = null;
    JButton button = null;

    public FirstProject(){
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        text = new JTextField();
        button = new JButton("GO");
        label = new JLabel("Result");
        button.addActionListener(this);
        
        this.getContentPane().setLayout(new BorderLayout());
        this.getContentPane().add(text,"North");
        this.getContentPane().add(button, "Center");
        this.getContentPane().add(label, "South");

        
        this.setSize(new Dimension(300, 90));
        this.setTitle("Test");
        this.setVisible(true);
    }

    public static void main(String[] args){
        new FirstProject();
    }

    public void actionPerformed(ActionEvent ae){
        if(ae.getActionCommand().equals("GO")){
            Pattern pattern = Pattern.compile(".+@.+\\..+");
            Matcher matcher = pattern.matcher(text.getText());
            if(matcher.matches()){
                label.setText("Good :-)");
            }else{            
                label.setText("Bad :-<");
            }
        }
    }
}