工厂模式

//数据库连接对象接口
public interface Connection {
    
    //创建连接语句
    void createStatement();
}

//mysql连接对象类
public class MysqlConnection implements Connection {

    @Override
    public void createStatement() {
        System.out.println("创建mysql连接语句!");
    }
}

//oracle连接对象类
public class OracleConnection implements Connection {

    @Override
    public void createStatement() {
        System.out.println("创建oracle连接语句!");
    }
}

//连接对象工厂类
public class ConnectionFactory {

    //根据传入的参数决定具体创建的对象
    public Connection createConnection(String key) {
        if(key == "mysql"){
            return new MysqlConnection();
        }
        else if (key == "oracle") {
            return new OracleConnection();
        }
        else {
            return null;
        }
    }
}

//测试类
public class Test {
    
    public static void main(String[] args) {
        
        String key1 = "mysql";
        String key2 = "oracle";
        
        ConnectionFactory factory = new ConnectionFactory();
        
        //创建mysql连接对象
        Connection mysqlConnection = factory.createConnection(key1);
        mysqlConnection.createStatement();
        
        //创建oracle连接对象
        Connection oracleConnection = factory.createConnection(key2);
        oracleConnection.createStatement();
    }
}

输出结果：
创建mysql连接语句!
创建oracle连接语句!