ELEMENTARY PROGRAMMING - Introduction to Java Programming: Comprehensive Version - page 42

After a variable is declared, you can assign a value to it by using an assignment statement. In
Java, the equal sign ( = ) is used as the assignment operator. The syntax for assignment state-
ments is as follows:

assignment statement
assignment operator

variable = expression;

An expression represents a computation involving values, variables, and operators that,
taking them together, evaluates to a value. For example, consider the following code:

expression

int y = 1 ; // Assign 1 to variable y
double radius = 1.0 ; // Assign 1.0 to variable radius
int x = 5 * ( 3 / 2 ); // Assign the value of the expression to x
x = y + 1 ; // Assign the addition of y and 1 to x
double area = radius * radius * 3.14159 ; // Compute area

You can use a variable in an expression. A variable can also be used in both sides of the =
operator. For example,

x = x + 1 ;

In this assignment statement, the result of x + 1 is assigned to x . If x is 1 before the state-
ment is executed, then it becomes 2 after the statement is executed.
To assign a value to a variable, you must place the variable name to the left of the assign-
ment operator. Thus, the following statement is wrong:

1 = x; // Wrong

Note
In mathematics, x = 2 * x + 1 denotes an equation. However, in Java, x = 2 * x
+ 1 is an assignment statement that evaluates the expression 2 * x + 1 and assigns
the result to x .

In Java, an assignment statement is essentially an expression that evaluates to the value
to be assigned to the variable on the left side of the assignment operator. For this reason, an
assignment statement is also known as an assignment expression. For example, the following
statement is correct:

assignment expression

System.out.println(x = 1 );

which is equivalent to

x = 1 ;
System.out.println(x);

If a value is assigned to multiple variables, you can use this syntax:

i = j = k = 1 ;

which is equivalent to

k = 1 ;
j = k;
i = j;

Note
In an assignment statement, the data type of the variable on the left must be compat-
ible with the data type of the value on the right. For example, int x = 1.0 would be