Learn English – Using “the” with names of functions, variables, constants in computer literature

"Literature" is a noncount abstract noun. When we use such nouns generically, to describe "literature in general", we usually don't use the definite article.

He is studying literature.

We also usually don't use the definite article if the noncount abstract noun is pre-modified (has a describing word before it):

He is studying English literature.

If the nouncount abstract noun is post-modified (especially by an of-phrase), we usually use the definite article:

He is studying the literature of England.

The same probably applies to the whole phrase "English literature": if it has a post-modifying phrase, we can use the definite article. I've found an example on Google Books:

... 'a moral force of great significance,' he showed, as often in his judgments of men, an insight which, at the same time, was prophetic; for Carlyle, unquestionably, was the strongest moral force in the English literature of the nineteenth century. Ward, Waller, 1909

In most cases though, especially if there's no post-modifying phrase, I believe the predominant form will be without the definite article:

Hamlet is one of the most famous works in English literature.

Let's use Ngram for a rough estimate:

The graph reflecting "in the English literature" could be partly explained by the presence of constructions like

He has chosen to enroll in the English literature course. ("the English literature" serves as an adjective to the word "course", and not as a noun phrase in its own right)

However, we should remember that the word "literature" can mean different things. It can mean "a body of scientific publications", and in some contexts your example phrase can mean "the collection of scientific papers devoted to a particular issue and published in English". Here's an excerpt from "Multiple Sclerosis: The History of a Disease" by Dr. T. Jock Murray, MS:

Here the author, being a native speaker of English, uses "the" in "in the English literature" even though the phrase is not post-modified. This usage also contribues to the red low-lying graph on the Ngram.

Reference:

Quirk et al., "A Comprehensive Grammar of the English Language", Unit 5.58, "The articles with abstract noncount nouns"

According to the Cambridge Dictionary, you have missed another case:

the

used before some nouns that refer to place when you want to mention that type of place, without showing exactly which example of the place you mean

We spent all day at the beach.
Let's go to the movies this evening.
I have to go to the bank and get some Euros

I think that the forest, the classroom, the airport and the sea in your phrases perfectly match this case.

Also, you may be right pointing out that the use of 'a' is fair in some of those phrases.

a

used to mean any or every thing or person of the type you are referring to

An airport and a sea fulfill this meaning but in my opinion you can't use a in your other phrases. They went to a specific forest. Asian students do not lunch in some classroom, they lunch in the same classroom where they are taught. In Spain at least, in schools students do not change classroom, different teachers come to the classroom.