Is it possible to create your own exceptions?

You can create your own exceptions easily by making them a subclass of an existing exception, such as Exception, the superclass of all exceptions. In a subclass of Exception, there are only two methods you might want to override: Exception() with no arguments and Exception() with a String as an argument. In the latter, the string should be a message describing the error that has occurred.

Why doesn't this hour cover how to throw and catch errors in addition to exceptions?

Java divides problems into Errors and Exceptions because they differ in severity. Exceptions are less severe, so they are something that should be dealt with in your programs using try-catch or throws. Errors, on the other hand, are more serious and can't be dealt with adequately in a program. Two examples of these errors are stack overflows and out-of-memory errors. These can cause the Java interpreter to crash, and there's no way you can fix them in your own program as the interpreter runs it.

In the children's song "This Old Man," what does the old man play knick-knack on when he reaches the number 12?

The rhymes vary in the song, which originated in the North Country of England during the 18th century. Some singers even vary the chorus, turning "knick-knack patty-whack" into "nick-nack cadillac." The old man begins with "he plays two, he plays knick-knack on my shoe," then moves on to the following things: three, knee; four, door or floor; five, hive or drive; six, bricks or sticks; seven, heaven or oven; eight, gate or plate; nine, line or all the time; and ten, hen or now and then. If he reaches 12, rhyming dictionaries offer only two decent possibilities for the old man: shelf or himself. Because the latter choice would give the song an R rating, it's safe to conclude that he plays knick-knack on my shelf with a knick-knack, paddy whack, give the dog a bone, then goes rolling home.