Answer:
Dialogue and the sequence of events in "After Twenty Years" work to reveal the characters of Jimmy and Bob along with the story's theme through the information they provide.
Dialogue to reveal characterization
In the exposition of the story the initial dialogue between the policeman and the apparent stranger who waits in a doorway for his old friend reveals some characteristics of both men. The stranger has had an arrangement with his friend, whom he terms "the finest chap in the world," to reunite at their favorite restaurant in twenty years. They have not seen each other because he has gone West to seek his fortune while no one "could have dragged Jimmy out of New York."
The policeman obtains more information about Jimmy after he asks if the man has heard from his old friend. The stranger replies that he did at first, but after a year or two,
"...we lost track of each other. You see, the West is a pretty big proposition, and I kept hustling around over it pretty lively."
But, the stranger adds that Jimmy will not forget their arrangement because he is "the truest, staunchest old chap in the world." Then, after the policeman asks if the stranger has done well out West, he replies,
"You bet! I hope Jimmy has done half as well. He was kind of a plodder, though good fellow that he was. I've had to compete with some of the sharpest wits going to get my pile."
This latter part of the exchange between the policeman and the stranger suggests some marked differences between the two friends. For one thing, the stranger's use of words about himself such as "hustling" and his saying he has had to compete with "the sharpest wits going to get my pile" hints at a nature.
