Variable names such as
sum actually correspond to locations in the computer’s memory. Every variable has a name, a type, a size (in bytes) and a value.
In the addition program of Fig. 2.7, when the following statement (line 18) executes:
number1 = input.nextInt(); // read first number from user
the number typed by the user is placed into a memory location corresponding to the name
number1. Suppose that the user enters
45. The computer places that integer value into location
number1 (Fig. 2.8), replacing the previous value (if any) in that location. The previous value is lost, so this process is said to be destructive.