PHP单例模式学习笔记详解_PHP教程

private static $_instance;

private function __construct()
{
//私有化默认构造方法，防止外界直接实例化
}
private function __clone()
{
//私有化克隆方法，防止用户复制实例
}

/**
 * 单例模式示例：Demo
 */
class Demo{
 //静态成员变量，用来保存全局实例
 private static $_instance;
 //私有化构造方法，保证外界不能直接实例化
 private function __construct(){

 }
 //私有化克隆方法，防止用户复制实例
 private function __clone(){

 }
 //返还此类的唯一实例
 public function getInstance(){
  if(!(self::$_instance instanceof self))
  {
   self::$_instance = new self();
  }
  return self::$_instance;
 }
 //这是第一个测试方法
 public function test1Function(){
  echo '这是第一个测试方法';
 }
 //这是第二个测试方法
 public function test2Function(){
  echo '这是第二个测试方法';
 }
}
//正确的使用方法
@$demo = Demo::getInstance();
$demo->test1Function();
$demo->test2Function();
//这样实例化会出错，因为构造方法为private
//$demo_new = new Demo;
//复制demo会出错，因为默认的clone方法为private
// $demo_clone = clone $demo;
?>

......
//初始化一个数据库句柄
$db = new DB(...);

//添加用户信息
$db->addUserInfo(...);

......

//在函数中访问数据库，查找用户信息
function getUserInfo()
{
    $db = new DB(...);//再次new 数据库类，和数据库建立连接
    $db = query(....);//根据查询语句访问数据库
}

?>

class DB 
{ 
    private $_db; 
    private static $_instance; 
 
    private function __construct(...) 
    { 
        $this->_db = pg_connect(...);//postgrsql 
    } 
 
    private function __clone() {};  //覆盖__clone()方法，禁止克隆 
 
    public static function getInstance() 
    { 
        if(! (self::$_instance instanceof self) ) { 
            self::$_instance = new self(); 
        } 
        return self::$_instance; 
    } 
 
   

    public function addUserInfo(...)
    {

    }

     public function getUserInfo(...)
    {

    }

}

//test

$db = DB::getInstance();

$db->addUserInfo(...);

$db->getUserInfo(...);

?>

class db {
 public $conn;
 public static $sql;
 public static $instance=null;
 private function __construct(){
  require_once('db.config.php');
  $this->conn = mysql_connect($db['host'],$db['user'],$db['password']);
  if(!mysql_select_db($db['database'],$this->conn)){
   echo "失败";
  };
  mysql_query('set names utf8',$this->conn);  
 }
 public static function getInstance(){
  if(is_null(self::$instance)){
   self::$instance = new db;
  }
  return self::$instance;
 }
 /**
  * 查询数据库
  */
 public function select($table,$condition=array(),$field = array()){
  $where='';
  if(!empty($condition)){
   
   foreach($condition as $k=>$v){
    $where.=$k."='".$v."' and ";
   }
   $where='where '.$where .'1=1';
  }
  $fieldstr = '';
  if(!empty($field)){
   
   foreach($field as $k=>$v){
    $fieldstr.= $v.',';
   }
    $fieldstr = rtrim($fieldstr,',');
  }else{
   $fieldstr = '*';
  }
  self::$sql = "select {$fieldstr} from {$table} {$where}";
  $result=mysql_query(self::$sql,$this->conn);
  $resuleRow = array();
  $i = 0;
  while($row=mysql_fetch_assoc($result)){
   foreach($row as $k=>$v){
    $resuleRow[$i][$k] = $v;
   }
   $i++;
  }
  return $resuleRow;
 }
 /**
  * 添加一条记录
  */
  public function insert($table,$data){
   $values = '';
   $datas = '';
   foreach($data as $k=>$v){
    $values.=$k.',';
    $datas.="'$v'".',';
   }
   $values = rtrim($values,',');
   $datas   = rtrim($datas,',');
   self::$sql = "INSERT INTO  {$table} ({$values}) VALUES ({$datas})";
  if(mysql_query(self::$sql)){
   return mysql_insert_id();
  }else{
   return false;
  };
  }
  /**
   * 修改一条记录
   */
 public function update($table,$data,$condition=array()){
  $where='';
  if(!empty($condition)){
   
   foreach($condition as $k=>$v){
    $where.=$k."='".$v."' and ";
   }
   $where='where '.$where .'1=1';
  }
  $updatastr = '';
  if(!empty($data)){
   foreach($data as $k=>$v){
    $updatastr.= $k."='".$v."',";
   }
   $updatastr = 'set '.rtrim($updatastr,',');
  }
  self::$sql = "update {$table} {$updatastr} {$where}";
  return mysql_query(self::$sql);
 }
 /**
  * 删除记录
  */
  public function delete($table,$condition){
   $where='';
  if(!empty($condition)){
   
   foreach($condition as $k=>$v){
    $where.=$k."='".$v."' and ";
   }
   $where='where '.$where .'1=1';
  }
  self::$sql = "delete from {$table} {$where}";
  return mysql_query(self::$sql);
  
  }
 
 public static function getLastSql(){
  echo self::$sql;
 }
 
 
 
}

$db = db::getInstance();
//$list = $db->select('demo',array('name'=>'tom','password'=>'ds'),array

('name','password'));
//echo $db->insert('demo',array('name'=>'最近你啦','password'=>'123'));
//echo $db->update('demo',array("name"=>'xxx',"password"=>'123'),array('id'=>1));
echo $db->delete('demo',array('id'=>'2'));
db::getLastSql();
echo "

";<br>
?>