php面向对象要点[转]

• __construct

<code><span><span><?php </span><span><span>class</span><span>ConstructTest</span> {</span><span>private</span><span>$arg1</span>;
    <span>private</span><span>$arg2</span>;

    <span>public</span><span><span>function</span><span>__construct</span><span>(<span>$arg1</span>, <span>$arg2</span>)</span> {</span><span>$this</span>->arg1 = <span>$arg1</span>;
        <span>$this</span>->arg2 = <span>$arg2</span>;
        <span>print</span><span>"__construct is called...\n"</span>;
    }
    <span>public</span><span><span>function</span><span>printAttributes</span><span>()</span> {</span><span>print</span><span>'$arg1 = '</span>.<span>$this</span>->arg1.<span>' $arg2 = '</span>.<span>$this</span>->arg2.<span>"\n"</span>;
    }
}
<span>$testObject</span> = <span>new</span> ConstructTest(<span>"arg1"</span>,<span>"arg2"</span>); 
<span>$testObject</span>->printAttributes();</span></span></code>

运行结果如下：

<code><span>Stephens</span>-<span>Air</span><span>:Desktop</span><span>$ </span>php <span>Test</span>.php 
__construct is called...
<span>$arg1</span> = arg1 <span>$arg2</span> = arg2</code>

• parent

用于在子类中直接调用父类中的方法

<code><span><span><?php </span><span><span>class</span><span>BaseClass</span> {</span><span>protected</span><span>$arg1</span>;
    <span>protected</span><span>$arg2</span>;

    <span><span>function</span><span>__construct</span><span>(<span>$arg1</span>, <span>$arg2</span>)</span> {</span><span>$this</span>->arg1 = <span>$arg1</span>;
        <span>$this</span>->arg2 = <span>$arg2</span>;
        <span>print</span><span>"__construct is called...\n"</span>;
    }
    <span><span>function</span><span>getAttributes</span><span>()</span> {</span><span>return</span><span>'$arg1 = '</span>.<span>$this</span>->arg1.<span>' $arg2 = '</span>.<span>$this</span>->arg2;
    }
}

<span><span>class</span><span>SubClass</span><span>extends</span><span>BaseClass</span> {</span><span>protected</span><span>$arg3</span>;

    <span><span>function</span><span>__construct</span><span>(<span>$baseArg1</span>, <span>$baseArg2</span>, <span>$subArg3</span>)</span> {</span><span>parent</span>::__construct(<span>$baseArg1</span>, <span>$baseArg2</span>);
        <span>$this</span>->arg3 = <span>$subArg3</span>;
    }
    <span><span>function</span><span>getAttributes</span><span>()</span> {</span><span>return</span><span>parent</span>::getAttributes().<span>' $arg3 = '</span>.<span>$this</span>->arg3;
    }
}
<span>$testObject</span> = <span>new</span> SubClass(<span>"arg1"</span>,<span>"arg2"</span>,<span>"arg3"</span>); 
<span>print</span><span>$testObject</span>->getAttributes().<span>"\n"</span>;</span></span></code>

运行结果如下：

<code><span>Stephens</span>-<span>Air</span><span>:Desktop</span><span>$ </span>php <span>Test</span>.php 
__construct is called...
<span>$arg1</span> = arg1 <span>$arg2</span> = arg2 <span>$arg3</span> = arg3</code>

• self
  在类内调用该类静态成员和静态方法的前缀修饰，对于非静态成员变量和函数则使用this。

<code><span><span><?php </span><span><span>class</span><span>StaticExample</span> {</span><span>static</span><span>public</span><span>$arg1</span> = <span>"Hello, This is static field.\n"</span>;
    <span>static</span><span>public</span><span><span>function</span><span>sayHello</span><span>()</span> {</span><span>print</span><span>self</span>::<span>$arg1</span>;
    }
}

<span>print</span> StaticExample::<span>$arg1</span>;
StaticExample::sayHello();</span></span></code>

• static
  这里介绍的static关键字主要用于PHP 5.3以上版本新增的延迟静态绑定功能。

<code><span><span><?php </span><span>abstract</span><span><span>class</span><span>Base</span> {</span><span>public</span><span>static</span><span><span>function</span><span>getInstance</span><span>()</span> {</span><span>//这里的new static()实例化的是调用该静态方法的当前类。</span><span>return</span><span>new</span><span>static</span>();
    }
    <span>abstract</span><span>public</span><span><span>function</span><span>printSelf</span><span>()</span>;</span>}

<span><span>class</span><span>SubA</span><span>extends</span><span>Base</span> {</span><span>public</span><span><span>function</span><span>printSelf</span><span>()</span> {</span><span>print</span><span>"This is SubA::printSelf.\n"</span>;
    }
}

<span><span>class</span><span>SubB</span><span>extends</span><span>Base</span> {</span><span>public</span><span><span>function</span><span>printSelf</span><span>()</span> {</span><span>print</span><span>"This is SubB::printSelf.\n"</span>;
    }
}

SubA::getInstance()->printSelf();
SubB::getInstance()->printSelf();</span></span></code>

运行结果如下：

<code>Stephens-Air:Desktop$ php Test.php 
This <span>is</span> SubA<span>::printSelf.</span>
This <span>is</span> SubB<span>::printSelf.</span></code>

static关键字不仅仅可以用于实例化。和self和parent一样，static还可以作为静态方法调用的标识符，甚至是从非静态上下文中调用。在该场景下，self仍然表示的是当前方法所在的类。见如下代码：

<code><span><span><?php </span><span>abstract</span><span><span>class</span><span>Base</span> {</span><span>private</span><span>$ownedGroup</span>;
    <span>public</span><span><span>function</span><span>__construct</span><span>()</span> {</span><span>//这里的static和上面的例子一样，表示当前调用该方法的实际类。</span><span>//需要另外说明的是，这里的getGroup方法即便不是静态方法，也会得到相同的结果。然而倘若</span><span>//getGroup真的只是普通类方法，那么这里还是建议使用$this。</span><span>$this</span>->ownedGroup = <span>static</span>::getGroup();
    }
    <span>public</span><span><span>function</span><span>printGroup</span><span>()</span> {</span><span>print</span><span>"My Group is "</span>.<span>$this</span>->ownedGroup.<span>"\n"</span>;
    }
    <span>public</span><span>static</span><span><span>function</span><span>getInstance</span><span>()</span> {</span><span>return</span><span>new</span><span>static</span>();
    }
    <span>public</span><span>static</span><span><span>function</span><span>getGroup</span><span>()</span> {</span><span>return</span><span>"default"</span>;
    }
}

<span><span>class</span><span>SubA</span><span>extends</span><span>Base</span> {</span>
}

<span><span>class</span><span>SubB</span><span>extends</span><span>Base</span> {</span><span>public</span><span>static</span><span><span>function</span><span>getGroup</span><span>()</span> {</span><span>return</span><span>"SubB"</span>;
    }
}

SubA::getInstance()->printGroup();
SubB::getInstance()->printGroup(); </span></span></code>

运行结果如下：

<code>
Stephens-Air:Desktop$ php Test.php 
My <span>Group</span><span>is</span><span>default</span>
My <span>Group</span><span>is</span> SubB</code>

• __destruct
  析构方法的作用和构造方法__construct刚好相反，它只是在对象被垃圾收集器收集之前自动调用，我们可以利用该方法做一些必要的清理工作。

<code><span><span><?php </span><span><span>class</span><span>TestClass</span> {</span><span><span>function</span><span>__destruct</span><span>()</span> {</span><span>print</span><span>"TestClass destructor is called.\n"</span>;
    }
}

<span>$testObj</span> = <span>new</span> TestClass();
<span>unset</span>(<span>$testObj</span>);
<span>print</span><span>"Application will exit.\n"</span>;</span></span></code>

运行结果如下：

<code>
Stephens-Air:Desktop$ php Test.php 
TestClass <span><span>destructor</span><span>is</span><span>called</span>.
<span>Application</span><span>will</span><span>exit</span>.</span></code>

• __clone
  在PHP 5之后的版本中，对象之间的赋值为引用赋值，即赋值后的两个对象将指向同一地址空间，如果想基于对象赋值，可以使用PHP提供的clone方法。该方法将当前对象浅拷贝之后的副本返回，如果想在clone的过程中完成一些特殊的操作，如深拷贝，则需要在当前类的声明中实现__clone方法，该方法在执行clone的过程中会被隐式调用。另外需要格外注意的是，__clone方法是作用再被拷贝的对象上，即赋值后的对象上执行。

<code><span><span><?php </span><span><span>class</span><span>InnerClass</span> {</span><span>public</span><span>$id</span> = <span>10</span>;
    <span>public</span><span><span>function</span><span>printSelf</span><span>()</span> {</span><span>print</span><span>'$id = '</span>.<span>$this</span>->id.<span>"\n"</span>;
    }
}

<span><span>class</span><span>OuterClass</span> {</span><span>public</span><span>$innerClass</span>;
    <span>public</span><span><span>function</span><span>__construct</span><span>()</span> {</span><span>$this</span>->innerClass = <span>new</span> InnerClass();
    }
    <span>public</span><span><span>function</span><span>__clone</span><span>()</span> {</span><span>$this</span>->innerClass = <span>clone</span><span>$this</span>->innerClass;
        <span>print</span><span>"__clone is called.\n"</span>;
    }
}

<span>$outerA</span> = <span>new</span> OuterClass();
<span>print</span><span>"Before calling to clone.\n"</span>;
<span>$outerB</span> = <span>clone</span><span>$outerA</span>;
<span>print</span><span>"After calling to clone.\n"</span>;
<span>$outerA</span>->innerClass->id = <span>20</span>;
<span>print</span><span>"In outerA: "</span>;
<span>$outerA</span>->innerClass->printSelf();
<span>print</span><span>"In outerB: "</span>;
<span>$outerB</span>->innerClass->printSelf();</span></span></code>

运行结果如下：

<code>
Stephens<span>-Air</span>:Desktop$ php Test<span>.</span>php 
Before calling <span>to</span> clone<span>.</span>
__clone is called<span>.</span>
After calling <span>to</span> clone<span>.</span><span>In</span> outerA: <span>$id</span><span>=</span><span>20</span><span>In</span> outerB: <span>$id</span><span>=</span><span>10</span></code>

• const
  PHP5可以在类中定义常量属性。和全局常量一样，一旦定义就不能改变。常量属性不需要像普通属性那样以开头，按照惯例，只能用大写字母来命名常量。另外和静态属性一样，只能通过类而不能通过类的实例访问常量属性，引用常量时同样也不需要以

  以上就介绍了php面向对象要点[转]，包括了方面的内容，希望对PHP教程有兴趣的朋友有所帮助。