Classes and Objects - Beginning Java 8 Fundamentals - page 189

The above call to the add method passes 10 and 12 as the values for parameters n1 and n2 , respectively. The two
values, 10 and 12, that are used to call the add method are called actual parameters. Java copies the actual parameters
to the formal parameters before it executes the code inside the body of the method. In the above call to the add
method, 10 will be copied in n1 , and 12 will be copied in n2 . You can refer to the formal parameter names as variables
having actual parameter values inside the method's body. You can see n1 and n2 being treated as variables in the
following statement in the add method:
int sum = n1 + n2;
A return statement is used to return a value from a method. It starts with the return keyword. If a method
returns a value, the return keyword must be followed by an expression, which evaluates to the value being returned.
If the method does not return a value, its return type is specified as void . If the method's return type is void , the
method does not have to include a return statement. If a method with a void return type wants to include a return
statement, the return keyword must not be followed by any expression; the return keyword is immediately followed
by a semicolon to mark the end of the statement. Here are the two flavors of the return statement:
// If a method returns a value, <<an expression>>must evaluate to a data type,
// which is assignment compatible with the specified return type of the method
return <<an expression>>;
or
// If method's return type is void
return;
What does a return statement do? As its name suggests, it returns the control to the caller of the method. If it has
an expression, it evaluates the expression and returns the value of the expression to the caller. If a return statement
does not have an expression, it simply returns the control to its caller. A return statement is the last statement that is
executed in a method's body. You can have multiple return statements in a method's body. However, at most, only
one return statement may be executed for a method call.
The add method returns the sum of two of its parameters. How do you capture the returned value of a method?
A method call itself is an expression whose data type is the return type of the method and it evaluates to the returned
value from the method. For example, if you write a statement like
add(10, 12);
add(10, 12) is an expression and its data type is int . At runtime, it will be evaluated to an int value of 22,
which is the value returned from the add method. To capture the value of a method call, you can use the method call
expression anywhere you can use a value. For example, the following snippet of code assigns the value returned from
the add method to a variable call sum :
int sum = add(10, 12); // sum variable will be assigned 22
Now turn your attention to a method, which does not return a value. You specify void as the return type for such
a method. Let's consider the following method declaration for a method printPoem ;
void printPoem() {
System.out.println("Strange fits of passion have I known:");
System.out.println("And I will dare to tell,");
System.out.println("But in the lover's ear alone,");
System.out.println("What once to me befell.");
}