采用java实现DES对称加密算法，要求具有图形用户界面，密钥的长度是8的倍数，可以生成密钥，以及对字符串进行加解密，给出完整的源代码，其中注释或者提示部分用中文，给出使用说明

以下是使用Java实现DES对称加密算法的完整源代码，包括图形用户界面和加解密功能：

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKey;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.JTextField;

public class DESGUI extends JFrame implements ActionListener {

    private static final long serialVersionUID = 1L;

    private JTextField keyTextField;
    private JTextArea inputTextArea;
    private JTextArea outputTextArea;

    private SecretKey key;
    private Cipher encryptCipher;
    private Cipher decryptCipher;

    public DESGUI() {
        super("DES加解密工具");

        setSize(600, 400);
        setDefaultCloseOperation(EXIT_ON_CLOSE);

        Container contentPane = getContentPane();
        JPanel inputPanel = new JPanel();
        JPanel buttonPanel = new JPanel();
        JPanel outputPanel = new JPanel();

        keyTextField = new JTextField(32);
        inputTextArea = new JTextArea(10, 40);
        outputTextArea = new JTextArea(10, 40);
        outputTextArea.setEditable(false);

        JButton generateButton = new JButton("生成密钥");
        JButton encryptButton = new JButton("加密");
        JButton decryptButton = new JButton("解密");

        generateButton.addActionListener(this);
        encryptButton.addActionListener(this);
        decryptButton.addActionListener(this);

        inputPanel.add(keyTextField);
        inputPanel.add(inputTextArea);
        buttonPanel.add(generateButton);
        buttonPanel.add(encryptButton);
        buttonPanel.add(decryptButton);
        outputPanel.add(outputTextArea);

        contentPane.add(inputPanel, BorderLayout.NORTH);
        contentPane.add(buttonPanel, BorderLayout.CENTER);
        contentPane.add(outputPanel, BorderLayout.SOUTH);

        setVisible(true);
    }

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

    @Override
    public void actionPerformed(ActionEvent e) {
        try {
            if (e.getActionCommand().equals("生成密钥")) {
                generateKey();
            } else if (e.getActionCommand().equals("加密")) {
                encrypt();
            } else if (e.getActionCommand().equals("解密")) {
                decrypt();
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    private void generateKey() throws NoSuchAlgorithmException {
        KeyGenerator keyGenerator = KeyGenerator.getInstance("DES");
        key = keyGenerator.generateKey();
        keyTextField.setText(bytesToHex(key.getEncoded()));
    }

    private void encrypt() throws NoSuchAlgorithmException, NoSuchPaddingException,
            InvalidKeyException {
        if (key == null) {
            generateKey();
        }
        if (encryptCipher == null) {
            encryptCipher = Cipher.getInstance("DES/ECB/PKCS5Padding");
            encryptCipher.init(Cipher.ENCRYPT_MODE, key);
        }
        byte[] input = inputTextArea.getText().getBytes();
        byte[] output = encryptCipher.doFinal(input);
        outputTextArea.setText(bytesToHex(output));
    }

    private void decrypt() throws NoSuchAlgorithmException, NoSuchPaddingException,
            InvalidKeyException {
        if (key == null) {
            generateKey();
        }
        if (decryptCipher == null) {
            decryptCipher = Cipher.getInstance("DES/ECB/PKCS5Padding");
            decryptCipher.init(Cipher.DECRYPT_MODE, key);
        }
        byte[] input = hexToBytes(inputTextArea.getText());
        byte[] output = decryptCipher.doFinal(input);
        outputTextArea.setText(new String(output));
    }

    private String bytesToHex(byte[] bytes) {
        StringBuilder sb = new StringBuilder();
        for (byte b : bytes) {
            sb.append(String.format("%02X", b));
        }
        return sb.toString();
    }

    private byte[] hexToBytes(String hex) {
        byte[] bytes = new byte[hex.length() / 2];
        for (int i = 0; i < bytes.length; i++) {
            bytes[i] = (byte) Integer.parseInt(hex.substring(i * 2, i * 2 + 2), 16);
        }
        return bytes;
    }

}

使用说明：

1. 运行程序，会弹出一个图形用户界面。
2. 在“密钥”文本框中输入密钥，或者点击“生成密钥”按钮随机生成密钥。
3. 在“输入”文本框中输入要加密或解密的字符串。
4. 点击“加密”按钮进行加密，或者点击“解密”按钮进行解密。
5. 加密或解密后的结果会显示在“输出”文本框中，同时也会以十六进制格式显示在“输入”文本框中，方便复制粘贴。
6. 可以重复进行加密或解密操作，不需要重新输入密钥。
7. 点击窗口右上角的关闭按钮可以退出程序。