PHP explode()函数的几个应用和implode()函数有什么区

<?php
// Example 
$fruit = "Apple Banana Orange Lemon Mango Pear";
$fruitArray = explode(" ", $fruit);
echo $fruitArray[]; // Apple
echo $fruitArray[]; // Banana
// Example 
$data = "gonn::nowamagic:::/home/foo:/bin/sh";
list($user, $pass, $uid, $gid, $gecos, $home, $shell) = explode(":", $data);
echo $user; // gonn
echo $pass; // 
?>

<?php
$str = 'one|two|three|four';
// positive limit
print_r(explode('|', $str, ));
// negative limit (since PHP .)
print_r(explode('|', $str, -));
?>

Array
(
  [] => one
  [] => two|three|four
)
Array
(
  [] => one
  [] => two
  [] => three
)

<?php
// converts pure string into a trimmed keyed array
function stringKeyedArray($string, $delimiter = ',', $kv = '=>') {
 if ($a = explode($delimiter, $string)) { // create parts
  foreach ($a as $s) { // each part
   if ($s) {
    if ($pos = strpos($s, $kv)) { // key/value delimiter
     $ka[trim(substr($s, , $pos))] = trim(substr($s, $pos + strlen($kv)));
    } else { // key delimiter not found
     $ka[] = trim($s);
    }
   }
  }
  return $ka;
 }
} // stringKeyedArray
$string = 'a=>, b=>, $a, c=>%, true, d=>ab c';
print_r(stringKeyedArray($string));
?>

<?php 
$arr = array('Hello','World!','Beautiful','Day!'); 
echo implode(" ",$arr); 
?>