PHP infinite classification tree code_PHP tutorial

/**
by lenush;
*/
class Tree
{
var $data = array();
var $child = array(-1=>array());
var $layer = array(-1=>-1);
var $parent = array();

function Tree ($value)
{
$this->setNode(0, -1, $value);
} // end func

function setNode ($id, $parent, $value)
{
$parent = $parent?$parent:0;

$this->data[$id] = $value;
$this->child[$id] = array();
$this->child[$parent][] = $id;
$this->parent[$id] = $parent;

if (!isset($this->layer[$parent]))
{
$this->layer[$id] = 0;
}
else
{
$this->layer[$id] = $this->layer[$parent] + 1;
}
} // end func

function getList (&$tree, $root= 0)
{
foreach ($this->child[$root] as $key=>$id)
{
$tree[] = $id;

if ($this->child[$id]) $this->getList($tree, $id);
}
} // end func


function getValue ($id)
{
return $this->data[$id];
} // end func


function getLayer ($id, $space = false)
{
return $space?str_repeat($space, $this->layer[$id]):$this->layer[$id];
} // end func

function getParent ($id)
{
return $this->parent[$id];
} // end func

function getParents ($id)
{
while ($this->parent[$id] != -1)
{
$id = $parent[$this->layer[$id]] = $this->parent[$id];
}

ksort($parent);
reset($parent);

return $parent;
} // end func

function getChild ($id)
{
return $this->child[$id];
} // end func

function getChilds ($id = 0)
{
$child = array($id);
$this->getList($child, $id);

return $child;
} // end func
} // end class


//new Tree(根目录的名字);
//根目录的ID自动分配为0
$Tree = new Tree('目录导航');

//setNode(目录ID,上级ID，目录名字);
$Tree->setNode(1, 0, '目录1');
$Tree->setNode(2, 1, '目录2');
$Tree->setNode(3, 0, '目录3');
$Tree->setNode(4, 3, '目录3.1');
$Tree->setNode(5, 3, '目录3.2');
$Tree->setNode(6, 3, '目录3.3');
$Tree->setNode(7, 2, '目录2.1');
$Tree->setNode(8, 2, '目录2.2');
$Tree->setNode(9, 2, '目录2.3');
$Tree->setNode(10, 6, '目录3.3.1');
$Tree->setNode(11, 6, '目录3.3.2');
$Tree->setNode(12, 6, '目录3.3.3');

//getChilds(指定目录ID);
//取得指定目录下级目录.如果没有指定目录就由根目录开始
$category = $Tree->getChilds();

//遍历输出
foreach ($category as $key=>$id)
{
echo $Tree->getLayer($id, '|-').$Tree->getValue($id)."
n";
}
?>