一个php初学者的一个学习笔记的面向对象编程实例，有需要学习的朋友可参考下，脚本之家也更新了很多大家可以查阅下

<?php
class db { 
    private $mysqli; //数据库连接 
    private $options; //SQL选项 
    private $tableName; //表名 
    public function __construct($tabName) { 
        $this->tableName = $tabName; 
        $this->db (); 
    } 
    private function db() { 
        $this->mysqli = new mysqli ( 'localhost', 'root', '', 'hdcms' ); 
        $this->mysqli->query("SET NAMES GBK"); 
    } 
    public function fields($fildsArr) { 
        if (empty ( $fildsArr )) { 
            $this->options ['fields'] = ''; 
        } 
        if (is_array ( $fildsArr )) { 
            $this->options ['fields'] = implode ( ',', $fildsArr ); 
        } else { 
            $this->options ['fields'] = $fildsArr; 
        } 
        return $this; 
    } 
    public function order($str) { 
        $this->options ['order'] = "ORDER BY " . $str; 
        return $this; 
    } 
    public function select() { 
        $sql = "SELECT {$this->options['fields']} FROM {$this->tableName}  {$this->options['order']}"; 
        return $this->query ( $sql ); 
    } 
    private function query($sql) { 
        $result = $this->mysqli 
            ->query ( $sql ); 
        $rows = array (); 
        while ( $row = $result->fetch_assoc () ) { 
            $rows [] = $row; 
        } 
        return $rows; 
    } 
    private function close() { 
        $this->mysqli 
            ->close (); 
    } 
    function __destruct() { 
        $this->close (); 
    } 
} 
$chanel = new db ( "hdw_channel" ); 
$chanelInfo = $chanel->fields ( 'id,cname,cpath' ) 
    ->select (); 
echo "<pre>"; 
print_r ( $chanelInfo );

class a { 
    protected  function aa(){ 
        echo 222; 
    } 
} 
class b extends a{ 
    function bb(){ 
        $this->aa(); 
    } 
} 
$c = new b(); 
$c->bb();

public   公有的：本类，子类，外部对象都可以调用
protected 受保护的：本类 子类，可以执行，外部对象不可以调用
private 私有的：只能本类执行，子类与外部对象都不可调用