Java中常用的加密算法有DES、AES、RSA等。以下是這些算法的應用示例：

1. DES加密算法的應用示例：

import javax.crypto.*;
import javax.crypto.spec.DESKeySpec;
import javax.crypto.spec.SecretKeySpec;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.NoSuchAlgorithmException;
import java.security.spec.InvalidKeySpecException;

public class DESExample {
    public static void main(String[] args) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, InvalidKeySpecException, BadPaddingException, IllegalBlockSizeException {
        String plaintext = "Hello, world!";
        String keyString = "mysecretkey"; // 密鑰，長度必須為8字節

        // 生成密鑰
        SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("DES");
        DESKeySpec desKeySpec = new DESKeySpec(keyString.getBytes());
        SecretKey secretKey = keyFactory.generateSecret(desKeySpec);

        // 創建加密器
        Cipher cipher = Cipher.getInstance("DES/ECB/PKCS5Padding");
        cipher.init(Cipher.ENCRYPT_MODE, secretKey);

        // 加密
        byte[] encryptedBytes = cipher.doFinal(plaintext.getBytes());
        System.out.println("Encrypted: " + new String(encryptedBytes));

        // 創建解密器
        cipher.init(Cipher.DECRYPT_MODE, secretKey);

        // 解密
        byte[] decryptedBytes = cipher.doFinal(encryptedBytes);
        System.out.println("Decrypted: " + new String(decryptedBytes));
    }
}

2. AES加密算法的應用示例：

import javax.crypto.*;
import javax.crypto.spec.SecretKeySpec;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.NoSuchAlgorithmException;

public class AESExample {
    public static void main(String[] args) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException {
        String plaintext = "Hello, world!";
        String keyString = "mysecretkey123456"; // 密鑰，長度必須為16字節

        // 生成密鑰
        Key key = new SecretKeySpec(keyString.getBytes(), "AES");

        // 創建加密器
        Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
        cipher.init(Cipher.ENCRYPT_MODE, key);

        // 加密
        byte[] encryptedBytes = cipher.doFinal(plaintext.getBytes());
        System.out.println("Encrypted: " + new String(encryptedBytes));

        // 創建解密器
        cipher.init(Cipher.DECRYPT_MODE, key);

        // 解密
        byte[] decryptedBytes = cipher.doFinal(encryptedBytes);
        System.out.println("Decrypted: " + new String(decryptedBytes));
    }
}

3. RSA加密算法的應用示例：

import javax.crypto.Cipher;
import java.nio.charset.StandardCharsets;
import java.security.*;

public class RSAExample {
    public static void main(String[] args) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException {
        String plaintext = "Hello, world!";

        // 生成密鑰對
        KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
        keyGen.initialize(2048);
        KeyPair keyPair = keyGen.generateKeyPair();
        PublicKey publicKey = keyPair.getPublic();
        PrivateKey privateKey = keyPair.getPrivate();

        // 創建加密器
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);

        // 加密
        byte[] encryptedBytes = cipher.doFinal(plaintext.getBytes(StandardCharsets.UTF_8));
        System.out.println("Encrypted: " + new String(encryptedBytes));

        // 創建解密器
        cipher.init(Cipher.DECRYPT_MODE, privateKey);

        // 解密
        byte[] decryptedBytes = cipher.doFinal(encryptedBytes);
        System.out.println("Decrypted: " + new String(decryptedBytes));
    }
}

以上示例分別演示了DES、AES和RSA加密算法的使用方法，包括生成密鑰、創建加密器、加密和解密操作。請注意，密鑰的長度必須滿足算法要求，否則會拋出異常。加密和解密時使用的密鑰必須匹配。