Some doubts about how the loop work (trying debugging it)

Question

I am very new in WordPress development (and also in PHP development, I came from Java and C#). Today I have installed Aptana and configured XDebug to inspect what happens into the TwentyTwelve theme.

In particular, I am trying to understand how WordPress load the posts in the loop (debbuging it).

So, up until now, I only know how create a loop in a WP theme, but I don't know how exactly it work.

So, in the TwentyTwelve I find the post loop, this code snippet:

<?php while ( have_posts() ) : the_post(); ?>
    <?php get_template_part( 'content', get_post_format() ); ?>
<?php endwhile; ?>

From what I can understand the loop is composed by a while() cycle where the have_posts() result is the condition to execute the while body.

Ok, now probabily the following question is related to my ignorance in PHP, but what exactly does this construction means:

<?php while ( have_posts() ) : the_post(); ?>

have_posts() is the condition to execute in the while but what exactly means the : the_post();

Is the_post() call the first operation of the cycle or what?

Then I have put a breakpoint into the have_posts() function definied into the query.php file.

function have_posts() {
    global $wp_query;

    return $wp_query->have_posts();
}

What exactly is the query.php file? Is it a class or what? Looking at its code it seems to me that it is not a class. Why?

And what exactly represent $wp_query variable? Is it an object or what? (PHP is not typed so how can I know what a variable contains?)

What means this operation:

$wp_query->have_posts();

I think that it call another version of the have_posts() function (definied into the query.php file) that check if exist some other post to show or if they are ended.

But how exactly work? Reading the PHP OO documentation the -> operator call a method of an object but I don't know if $wp_query is an object or if in this contents the -> operator have another sense...

Can you help me to understand how exactly it work?

Answer 1

<?php
if (have_posts()) : while (have_posts()) : the_post();                                     endwhile;
 else:
 _e('No blog found.', 'polymer');
endif;
?>

if(have_post) condition is to check if the page contain post, while(have_posts) condition if there is more than one post display in loop, the_post() is used to display the post if(have_post) condition fails it will go to else loop. Tell for any further doubts.....