variable exception in java

why do you need a variable in catch exception and how do you use each it the same as the detailed exception?

TemperatureException and e
TooColdException and e

for example:

try {
cust.drinkCoffee(cup);
System.out.println("Coffee is just right.");
}
catch (TemperatureException e) {
// This catches TooColdException, TooHotException,
// as well as TemperatureException....

variable exception in java