BASIC ELEMENTS OF JAVA - Java Programming: From Problem Analysis to Program Design - page 53

A Java statement such as:
num = num + 2;

means ''evaluate whatever is in num , add 2 to it, and assign the new value to the memory
location num .'' The expression on the right side must be evaluated first; that value is then
assigned to the memory location specified by the variable on the left side. Thus, the
sequence of Java statements:

2

num = 6;
num = num + 2;
and the statement:

num = 8;

both assign 8 to num . Note that the statement num = num + 2 is meaningless if num has not
been initialized.
The statement num = 5; is read as '' num becomes 5 '' or '' num gets 5 '' or '' num is assigned
the value 5 .'' Each time a new value is assigned to num , the old value is erased.

Suppose that num is an int variable. Consider the statement: num = num + 2; . This
statement adds 2 to the value of num , and the new value is assigned to the variable num .
If the variable num is not properly initialized, then the Java complier will generate a
syntax error. So to use the value of a variable in an expression, the variable must
be properly initialized. Variable initialization is further covered in the next section,
''Declaring and Initializing Variables.''

EXAMPLE 2-14

Suppose that num1 , num2 , and num3 are int variables and the following statements are
executed in sequence.

1.

num1 = 18;

2. num1 = num1 + 27;

3.

num2 = num1;

4. num3 = num2 / 5;

5.

num3 = num3 / 4;

Table 2-4 shows the values of the variables after the execution of each statement. (A ?
indicates that the value is unknown. The orange color in a box shows that the value of
that variable is changed.)