Hi, I am programming under linux and I am reading single-word strings on separate lines of a file and adding them to a TreeSet object. Everything works fine and the TreeSet has the proper items, but I get the following warnings on the command line when I compile:

Note: foo.java uses unchecked or unsafe operations.
Note: Recompile with -xlint:unchecked for details.

Now, I've narrowed it down to the exact lines of code that cause this to happen; here they are:

try {
while ((myStr = in.readLine ()) ! = null)
myTreeSet.add (myStr);
}
catch (IOException e1) {
// blah blah
}
catch (ClassCastException e2) {
// blah blah
}

And this couldnt' possibly be due to my ignoring that boolean val returned when a TreeSet object adds. Please help. Thank you.

Sean

Java 1.5 supports Generics, which allows you to use Collections and many other classes and stuff such that you can specify all the elements as a certain type (has some similarities with templates in C++). e.g. TreeSet<String> instead of just TreeSet. This allows you to not need to (dangerously) manually cast elements when you retrieve them, allowing it to make typesafe checks at compile time.

This is a very useful feature if you use Java 1.5 (Java before 1.5 doesn't support it). Java 1.5 is backward-compatible in allowing you not to use Generics but complains "unchecked" operations.