Create Class PHP II

<?php
class electronics{

    protected $power;
    protected $display;
    protected $powerState = 'off';

    function changePowerState (){
        switch ($this->powerState){
            case 'off':
                $this->powerState = 'on';
                break;
            case 'on':
                $this->powerState = 'off';
                break;
            default :
                $this->powerState = 'off';
              break;
        }
    }

    function getPowerState(){
        return $this->powerState;
    }

    function getPower()  {
        return $this->power;
    }

    function setPower($type) {
        $this->power = $type;
    }

    function getDisplay()  {
        return $this->display;
    }

    function setDisplay($type) {
        $this->display = $type;
    }

    function __construct($power,$display){
        $this->display = $display;
        $this->power = $power;
    }

}


class television extends electronics{

    protected $screenSize;
    protected $inputs = 1;
    protected $volume = 5;


    function increaseVolume(){
        if( $this->volume >= 10 ) {
            $this->volume = 10;
        }
        else{
            $this->volume = $this->volume +1;
        }
    }

    function decreaseVolume(){
        if( $this->volume <= 0 ) {
            $this->volume = 0;
        }
        else{
            $this->volume = $this->volume -1;
        }
    }

    function getScreenSize()  {
        return $this->screenSize;
    }

    function getInputs()  {
        return $this->inputs;
    }

    function setInputs($num) {
        $this->inputs = $num;
    }

    function getVolume()  {
        return $this->volume;
    }

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

}

class smartphone extends electronics{

    protected $screenSize;
    protected $mediaVolume = 5;
    protected $volume = 5;
    protected $storage;
    protected $apps = array();

    function increaseVolume(){
        if( $this->volume >= 10 ) {
            $this->volume = 10;
        }
        else{
            $this->volume = $this->volume +1;
        }
    }

    function decreaseVolume(){
        if( $this->volume <= 0 ) {
            $this->volume = 0;
        }
        else{
            $this->volume = $this->volume -1;
        }
    }

    function increaseMediaVolume(){
        if( $this->mediaVolume >= 10 ) {
            $this->mediaVolume = 10;
        }
        else{
            $this->mediaVolume = $this->mediaVolume +1;
        }
    }

    function decreaseMediaVolume(){
        if( $this->mediaVolume <= 0 ) {
            $this->mediaVolume = 0;
        }
        else{
            $this->mediaVolume = $this->mediaVolume -1;
        }
    }

    function getScreenSize()  {
        return $this->screenSize;
    }

    function getVolume()  {
        return $this->volume;
    }

    function addApp($item){
        $this->apps[] = $item;
    }

    function removeApp($item){
       array_splice($this->apps, array_search($item, $this->apps),1);
    }

    function getApps(){
       return $this->apps;
    }

    function __construct($screenSize, $storage){
        $this->screenSize = $screenSize;
        $this->storage = $storage;
    }

}

$device = new electronics('AC', 'digital');

echo $device->getPower();
echo '<BR>';
echo $device->getPowerState();

$set = new television('AC', 'LCD', 32);
echo '<BR>';
echo $set->getPowerState();
echo '<BR>';
echo $set->getVolume();
echo '<BR>';
$set->increaseVolume();
echo $set->getVolume();
echo '<BR>';

$phone = new smartphone('AC','OLED',4.5, 64);