The Swing application written below takes text and a pattern as input and display whether the pattern was found in the text.

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

public class TestPatterns extends JFrame implements ActionListener {
    JTextArea text = new JTextArea(5, 29);
    JTextField pattern = new JTextField(35);
    JButton search = new JButton("Search");
    JButton newSearch = new JButton("New Search");
    JTextArea result = new JTextArea(5, 29);
 
    public TestPatterns() {
        super("Test Patterns");
        setSize(430, 320);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Container pane = getContentPane();
        GridLayout grid = new GridLayout(3, 1);
        pane.setLayout(grid);
        // set up the top row
        JLabel textLabel = new JLabel("Text: ");
        JPanel row1 = new JPanel();
        row1.add(textLabel);
        JScrollPane scroll = new JScrollPane(text,
            ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS,
            ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
        row1.add(scroll);
        // set up the middle row
        JPanel row2 = new JPanel();
        JLabel patternLabel = new JLabel("Pattern: ");
        row2.add(patternLabel);
        row2.add(pattern);
        search.addActionListener(this);
        newSearch.addActionListener(this);
        row2.add(search);
        row2.add(newSearch);
        // set up the bottom row
        JPanel row3 = new JPanel();
        JLabel resultLabel = new JLabel("Result: ");
        row3.add(resultLabel);
        result.setEditable(false);
        JScrollPane scroll2 = new JScrollPane(result,
            ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS,
            ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
        row3.add(scroll2);
        // set up the content pane
        pane.add(row1);
        pane.add(row2);
        pane.add(row3);
        setContentPane(pane);
        setVisible(true);
    }

    public void actionPerformed(ActionEvent evt) {
        Object source = evt.getSource();
        if (source == search) {
            checkPattern();
        } else {
            pattern.setText("");
            result.setText("");
        }
    }

    private void checkPattern() {
        try {
            if (Pattern.matches(pattern.getText(), text.getText()))
                result.setText("That pattern was found");
            else
                result.setText("That pattern was not found");
        } catch (PatternSyntaxException pse) {
            result.setText("Regex error: " + pse.getMessage());
        }
    }

    public static void main(String[] arguments) {
        TestPatterns app = new TestPatterns();
    }
}