我需要实现接受颜色作为字符串参数的函数，并将其作为json_encode返回

I want to get the function that can accept a string parameter and return it to json format. for example if i call $ballcolor->getBall("orange"); then the output// should be: { "color":"orange", "ball": ["basketball"]}

and if a call does not have any color for that ball: { "color":"black", "ball": []}

class BallColor
    {
      private $ballcolor;

      function BallColor($ballcolor)
      {
        $this->ballcolor = $ballcolor;
      }

      public function getBall($color)
      {

        return NULL;

      }
    }

    $ballcolor = new BallColor(array(
        "orange" => array("basketball"),
        "white" => array("football")
    ));

    echo $ballcolor->getBall("orange");
    echo "
";
    echo $ballcolor->getBall("black");

Get the desired value out of $this->ballcolor after checking it's there, then build the array you need to return, then json_encode that:

class BallColor
{
      private $ballcolor;

      function __construct($ballcolor)
      {
        $this->ballcolor = $ballcolor;
      }

      public function getBall($color)
      {
          // condensed into oneliners:
          if(isset($this->ballcolor[$color])) {
              return json_encode(Array("color" => $color, "ball" => $this->ballcolor[$color]));
          } else {
              return json_encode(Array("color" => "black", "ball" => []));
          }
      }
}

$ballcolor = new BallColor(array(
    "orange" => array("basketball"),
    "white" => array("football")
));

echo $ballcolor->getBall("orange");
echo "
";
echo $ballcolor->getBall("black");

Output:

{"color":"orange","ball":["basketball"]} 
{"color":"black","ball":[]}

you should use

function __construct($ballcolor)

instead of

function BallColor($ballcolor)

as you constructor, unless your php version is old.