For example, if a thrown exception object has class IllegalArgumentException, that indicates someone passed an illegal argument to a method. Sometimes you will want to indicate that a method encountered an abnormal condition that isn't represented by a class in the Throwable family of java.lang.
Actually, zero is neither a negative or a positive number. The whole idea of positive and negative is defined in terms of zero. Negative numbers are numbers that are smaller than zero, and positive numbers are numbers that are bigger than zero. Since zero isn't bigger or smaller than itself (just like you're not older than yourself, or taller than yourself), zero is neither positive nor negative.
I think it must be zero. Because the absolute value of a negative number is the positive of that number. and the absolute value of a positive number is the number itself. so we can say that the absolute value can be obtained by carelessly removing the sign(positive or negative). Since zero is neutral, its absolute value can be zero.