Why convert to a string

cornelombaard

Hi I am a newbie

I get the following error
Object of class Television could not be converted to string in C:\wamp\www\Learn\chapter8\interface.php on line 83

I want to know why php is trying to convert the object to a string?

Here is the code:

interface Sellable {
public function addStock ($numItems);
public function sellItem();
public function getStockLevel();
}

class Television implements Sellable {
    private $_screenSize;
    private $_stockLevel;

public function getScreenSize() {
    return $this->_screenSize;   

}
public function setScreenSize($screenSize) {
    $this->_screenSize = $screenSize;
}
public function addStock($numItems) {
    $this->_stockLevel += $numItems;
}
public function sellItem() {
    if($this->stockLevel > 0) {
        $this->_stockLevel--;
        return true;
    } else {
        return false;
    }
}
public function getStockLevel() {
    return $this->_stockLevel;
}
}

Class TennisBall implements Sellable {
    private $_color;
    private $_ballsLeft;


public function getColor() {
    return $this->_color;
}
public function setColor($color) {
    $this->_color = $color;
}
public function addStock($numItems) {
    $this->_ballsLeft =+ $numItems;
}
public function sellItem() {
    if($this->_ballsLeft > 0){
        $this->ballsLeft--;   

        return true;
} else {
    return false;
}
}
public function getStockLevel() {
    return $this->_ballsLeft;
}
}
class StoreManager {
    private $_productList = array();

public function addProduct(Sellable $product) {
    $this->_productlist[] = $product;
}
public function stockUp() {
    foreach($this->_productList as $product) {
        $product->addStock(100);
    }
}
}

$tv = new Television;
$tv->setScreenSize(42);
$ball = new TennisBall;
$ball->setColor("yellow");
$manager = new StoreManager();
$manager->addProduct($tv);
$manager->addProduct($ball);
$manager->stockUp();
echo "<p>There are " . $tv-getStockLevel() . " " . $tv->getScreenSize();
echo "-inch televisions and " . $ball->getStockLevel() . " " . $ball->getColor();
echo " temmis balls in stock</p>";
echo "<p>Selling television.. </p>";
$tv->sellItem();
echo "<p>Selling tennis balls</p>";
$ball->sellItem();
$ball->sellItem();
echo "<p>There are now " . $tv->getStockLevel() . " " . $tv->getScreenSize();
echo "-inch televisions left and " . $ball->getStockLevel() . " " . $ball->getColor();
echo " tennis balls left</p>";

?>

Any help and some explanation of how it works will be greatly appreciated thanx

sneakyimp

For starters, please surround your code with the code formatting tags so it is properly formatted. It makes it a lot easier to read.

dalecosp

Hello, and welcome to PHPBuilder. Please read what Sneakyimp said above.

I get the following error
Object of class Television could not be converted to string in C:\wamp\www\Learn\chapter8\interface.php on line 83

Typically, this happens when you to try print() an object, or use any function that expects a string argument using an object as the argument.

I'm not sure what's up, but you might first try removing "Sellable" from this:

public function addProduct(Sellable $product)

... and then see if the same error results.

Even if you're just copy/pasting your scripts, which I don't recommend, you should take the time to learn some basic PHP. "Sellable" isn't part of the language (and a simple visit to php.net would've confirmed this.

NogDog

In this context, "Sellable" would be the name of a class, being used for type-hinting in the function declaration (a run-time fatal error will occur if the supplied argument is not an object of that type [or one of its child classes]), so I doubt that's the issue here. I'm going to edit the OP to fix the tags, then see what we've got....

NogDog

The initial problem is that you omitted the ">" to complete the first "->" on this line:

echo "<p>There are " . $tv-[B][COLOR="#FF0000"]>[/COLOR][/B]getStockLevel() . " " . $tv->getScreenSize();

After you fix that, you'll find out that you left out the leading "_" of a property name. 😉

cornelombaard

Thank you! I have done what you said and it fixes the error but my problem now is that it is not working correctly and it is not showing the amounts of products left. On the one line it is supposed to add 100 Televisions and 100 tennis balls. Then it sells one television and one tennis ball so the final line should display that there are only 99 left of each but my code does not display that. Instead it only displays the following:

There are 42-inch televisions and yellow temmis balls in stock

Selling television..

Selling tennis balls

There are now 42-inch televisions left and yellow tennis balls left

I looked the code over again and it is correct according to the book and my logic but the resut is not correct so what is wrong and why is it not shwing the StockLevel?

I really appreciate your help

NogDog

Take a real close look at your class variable names. I see at least 2 places where you omitted the leading underscore on a couple of them. (One reason I'm not a big fan of the leading underscore convention for private class attributes.)

cornelombaard

Thanks for the help. I only found one class variable name not having the leading underscore and after fixing it I am sitting with the same problem and the amounts are not showing

Here is the revised code:


<?php

interface Sellable {
public function addStock ($numItems);
public function sellItem();
public function getStockLevel();
}

class Television implements Sellable {
    private $_screenSize;
    private $_stockLevel;

public function getScreenSize() {
    return $this->_screenSize;   

}
public function setScreenSize($screenSize) {
    $this->_screenSize = $screenSize;
}
public function addStock($numItems) {
    $this->_stockLevel += $numItems;
}
public function sellItem() {
    if($this->_stockLevel > 0) {
        $this->_stockLevel--;
        return true;
    } else {
        return false;
    }
}
public function getStockLevel() {
    return $this->_stockLevel;
}
}

Class TennisBall implements Sellable {
    private $_color;
    private $_ballsLeft;


public function getColor() {
    return $this->_color;
}
public function setColor($color) {
    $this->_color = $color;
}
public function addStock($numItems) {
    $this->_ballsLeft =+ $numItems;
}
public function sellItem() {
    if($this->_ballsLeft > 0){
        $this->_ballsLeft--;   

        return true;
} else {
    return false;
}
}
public function getStockLevel() {
    return $this->_ballsLeft;
}
}
class StoreManager {
    private $_productList = array();

public function addProduct(Sellable $product) {
    $this->_productlist[] = $product;
}
public function stockUp() {
    foreach($this->_productList as $product) {
        $product->addStock(100);
    }
}
}
$tv = new Television;
$tv->setScreenSize(42);
$ball = new TennisBall;
$ball->setColor("yellow");
$manager = new StoreManager();
$manager->addProduct($tv);
$manager->addProduct($ball);
$manager->stockUp();
echo "<p>There are " . $tv->getStockLevel() . " " . $tv->getScreenSize();
echo "-inch televisions and " . $ball->getStockLevel() . " " . $ball->getColor();
echo " tennis balls in stock</p>";
echo "<p>Selling television.. </p>";
$tv->sellItem();
echo "<p>Selling tennis balls</p>";
$ball->sellItem();
$ball->sellItem();
echo "<p>There are now " . $tv->getStockLevel() . " " . $tv->getScreenSize();
echo "-inch televisions left and " . $ball->getStockLevel() . " " . $ball->getColor();
echo " tennis balls left</p>";

Weedpacket

You will also want to pay attention to your use of upper- and lowercase letters in your variable names.

cornelombaard

Sorry I don't want to sound stupid but I have gone through everything and they are all the same and correct unless I am seriously going blind. So thanks for the help but you could you tell me where you see a mistake that way I don't have to go through line by line

laserlight

This:

$this->_productlist[] = $product;

should be:

$this->_productList[] = $product;

cornelombaard

Thank you very much that solved my problem.

NogDog

In summary, our lesson learned is that code parsers/compilers are too stupid to figure out what you meant: they only know exactly what you typed. 🙂

Weedpacket

Two or three pointers towards locating the cause of problems like this (i.e., debugging) at increasing degrees of sophistication:
[man]var_dump[/man] key variables at key points (such as immediately after the [font=monospace]StockUp()[/font] call, where it would have listed both [font=monospace]productlist[/font] and [font=monospace]productList[/font]);
XDebug for richer error messages, variable examination, and function traces;
phpdbg is available for PHP 5.4 and later, and is part of 5.6.