I had posted this very question long time ago, but I wasn't clear with my question. Well, I wanted to know which methods I ought to study from the String, StringBuffer, Thread, and the Collections Framework. Sun is very clear about which methods I need to know from the Math and Wrapper classes but does not state much for the classes String, StringBuffer, and Thread. There are a lot of methods from these classes which I have never used. Which methods should I study from the three classes I mentioned and the collections framework?
For String, know that equals() lexicographically compares two strings and that class methods that seem to change strings leave the invoking String unchanged and return a new String; in short, internalize that Strings are immutable.
(To illustrate an important difference between the StringBuffer and String methods, understand what is going on with, e.g., StringBuffer.append(StringBuffer sb) and String.concat(String str).)