Job requirements. Why do they write words with capital letters within sentences?

As far as Java and Android SDK are concerned, they're proper nouns.

Object-oriented programming is often written as OOP. Perhaps the author of the sentence thought it should be capitalised because the abbreviated form OOP has capitalised letters. The proper way of writing it would be 'object-oriented programming', since it is in the middle of a sentence.

Design patterns should not have capitalised letters - it isn't a proper noun, neither does it have an abbreviation; the author may have capitalised it for emphasis. Or he just isn't familiar with the rules of this language that well!