This very famous poem, which was used as the basis of the title for the famous play, A Raisin in the Sun, asks a question and gives us a series of possible answers without ever answering that question definitively. Instead, added emphasis is given to the way that the five answers are provided through the use of similes. For example, the speaker asks:
Does it dry up
like a raisin in the sun?
Each time, a different simile is used to give a possible answer, though the series of questions indicates that the speaker is only suggesting possibilities rather than definitive responses. It is the final line of the poem, however, which is given its own paragraph, that clearly adds a note of violence to the poem as a whole, as the speaker ends by asking: "Or does it explode?" Given the context in which Langston Hughes was writing and the complete lack of rights for African-Americans, such an ending adds the possibility of violence in the face of so much frustration and opposition to the dreams of moving towards equality. This powerful final metaphor completely changes the tone of the poem as Hughes uses it to paint a very clear picture of a group of people who can only wait so much longer.
Thus, although no clear answer is given, when we bear in mind the context of the poem, it is clear that Hughes is suggesting a "dream deferred" might actually lead people to become so frustrated that they "explode."