How is Jaques an introvert?

Jacques appropriately first appears "in character" (i.e. doing something characteristic). He is all alone, shunning companionship, and moralizing on the spectacle of a wounded deer being abandoned by the other members of the herd.
DUKE SENIOR.
But what said Jaques?
Did he not moralize this spectacle?
FIRST LORD.
O, yes, into a thousand similes.
First, for his weeping into the needless stream;
'Poor deer,' quoth he 'thou mak'st a testament
As worldlings do, giving thy sum of more
To that which had too much:' then, being there alone,
Left and abandoned of his velvet friends;
''Tis right'; quoth he; 'thus misery doth part
The flux of company:' anon, a careless herd,
Full of the pasture, jumps along by him
And never stays to greet him; 'Ay,' quoth Jaques,
'Sweep on, you fat and greasy citizens;
'Tis just the fashion; wherefore do you look
Upon that poor and broken bankrupt there?
'Thus most invectively he pierceth through
The body of the country, city, court,
Yea, and of this our life: swearing that we
Are mere usurpers, tyrants, and what's worse,
To fright the animals, and to kill them up
In their assign'd and native dwelling-place.
According to C. G. Jung, who coined the terms "introvert" and "extrovert," the introvert is interested in the "subjective" aspects of things--that is, in what they suggest to him--rather than the things in themselves. Jaques is an example of an introvert, a type of person who existed long before Jung identified them. According to Jung:
The introvert sees everything that is in any way valuable to him in the subject; the extravert sees it in the object. This dependence on the object seems to the introvert a mark of the greatest inferiority, while to the extravert the preoccupation with the subject seems nothing but infantile autoeroticism.
Jaques is very conspicuously preoccupied with what the object, the wounded deer, suggests to him, rather than in the spectacle presented by the animal itself. There are many introverts to be seen in literature. Hamlet is obviously one of them, as is Shakespeare's Richard II, and Brutus in his Julius Caesar. Herman Melville's character Bartleby in "Bartleby the Scrivener: A Tale of Wall Street" is a supreme example of an introvert. Stephen Dedalus in James Joyce's novel Ulysses is another. Rodion Raskolnikov in Dostoyevsky's novel Crime and Punishment is another introvert, as is the anonymous narrator of his novella Notes from Underground.
Jung states that, whereas extroverts never try to become introverts, it is common for introverts to try to act like extroverts because extroversion is the "dominant mode" in the Western world. According to Jung, it is destructive for an introvert to try to become an extrovert, and he generally does a very bad job of acting, like the narrator of Dostoyevsky's "Notes from Underground."
As a rule, whenever such a falsification of type takes place as a result of parental influence, the individual becomes neurotic later, and can be cured only by developing the attitude consonant with his nature.
Jung
What makes Jaques such an interesting example of an introvert is the fact that, along with dramatizing his persistence in avoiding people, Shakespeare emphasizes the intricate complexity of his subjectivity.