PHP 对象继承原理与简单用法示例

<?php

class foo
{
  public function printItem($string) 
  {
    echo 'Foo: ' . $string . PHP_EOL;
  }
  
  public function printPHP()
  {
    echo 'PHP is great.' . PHP_EOL;
  }
}

class bar extends foo
{
  public function printItem($string)
  {
    echo 'Bar: ' . $string . PHP_EOL;
  }
}

$foo = new foo();
$bar = new bar();
$foo->printItem('baz'); // Output: 'Foo: baz'
$foo->printPHP();    // Output: 'PHP is great' 
$bar->printItem('baz'); // Output: 'Bar: baz'
$bar->printPHP();    // Output: 'PHP is great'