import java.awt.GridLayout;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JTextField;
import javax.swing.SwingConstants;

public class MainFrame extends JFrame {
    private JTextField length1;
    private JTextField length2;
    private JTextField length3;
    private JTextField array[];

    public MainFrame() {
        init();
    }

    private void init() {
        length1 = createTextField("1");
        length2 = createTextField("2");
        length3 = createTextField("3");
        array = new JTextField[3];
        array[0] = length1;
        array[1] = length2;
        array[2] = length3;
        this.setLayout(new GridLayout(3, 2));
        this.add(new JLabel("边长A", SwingConstants.CENTER));
        this.add(length1);
        this.add(new JLabel("边长B", SwingConstants.CENTER));
        this.add(length2);
        this.add(new JLabel("边长C", SwingConstants.CENTER));
        this.add(length3);
        this.setSize(200, 150);
        this.setTitle("计算三角形面积");
        this.setVisible(true);
        this.setDefaultCloseOperation(EXIT_ON_CLOSE);
    }

    private JTextField createTextField(String name) {
        final JTextField t = new JTextField(6);
        t.setName(name);
        t.addKeyListener(new KeyListener() {

            @Override
            public void keyTyped(KeyEvent arg0) {
            }

            @Override
            public void keyReleased(KeyEvent arg0) {
            }

            @Override
            public void keyPressed(KeyEvent arg0) {
                if (arg0.getKeyCode() == KeyEvent.VK_SPACE) {
                    clear();
                    length1.grabFocus();
                } else if (arg0.getKeyCode() == KeyEvent.VK_ENTER) {
                    if (check()) {
                        JOptionPane
                                .showMessageDialog(MainFrame.this, getArea());
                    } else {
                        JOptionPane.showMessageDialog(MainFrame.this,
                                "请完整填写数据或者三条边无法构成三角形！");
                    }
                }
            }

        });
        return t;
    }

    private Object getArea() {
        return 123;
    }

    private void clear() {
        length1.setText("");
        length2.setText("");
        length3.setText("");
    }

    private boolean check() {
        for (JTextField t : array) {
            if (!t.getText().matches("^[0-9]+$")) {
                return false;
            }
        }
        int x = Integer.parseInt(length1.getText());
        int y = Integer.parseInt(length2.getText());
        int z = Integer.parseInt(length3.getText());
        if (x + y < z || x + z < y || y + z < x)
            return false;
        return true;
    }

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