METHODS - Introduction to Java Programming: Comprehensive Version - page 212

6.5 Passing Arguments by Values
The arguments are passed by value to parameters when invoking a method.

Key
Point

The power of a method is its ability to work with parameters. You can use println to print
any string and max to find the maximum of any two int values. When calling a method, you
need to provide arguments, which must be given in the same order as their respective param-
eters in the method signature. This is known as parameter order association. For example, the
following method prints a message n times:

parameter order association

public static void nPrintln(String message, int n) {
for ( int i = 0 ; i < n; i++)
System.out.println(message);
}

You can use nPrintln("Hello", 3) to print Hello three times. The nPrintln("Hello",
3) statement passes the actual string parameter Hello to the parameter message , passes 3 to
n , and prints Hello three times. However, the statement nPrintln(3, "Hello") would be
wrong. The data type of 3 does not match the data type for the first parameter, message , nor
does the second argument, Hello , match the second parameter, n .

Caution
The arguments must match the parameters in order, number, and compatible type, as
defined in the method signature. Compatible type means that you can pass an argument
to a parameter without explicit casting, such as passing an int value argument to a
double value parameter.

When you invoke a method with an argument, the value of the argument is passed to the
parameter. This is referred to as pass-by-value. If the argument is a variable rather than a
literal value, the value of the variable is passed to the parameter. The variable is not affected,
regardless of the changes made to the parameter inside the method. As shown in Listing 6.4,
the value of x ( 1 ) is passed to the parameter n to invoke the increment method (line 5). The
parameter n is incremented by 1 in the method (line 10), but x is not changed no matter what
the method does.

pass-by-value

L ISTING 6.4

Increment.java
1 public class Increment {
2 public static void main(String[] args) {
3 int x = 1 ;
4 System.out.println( "Before the call, x is " + x);
5 increment(x);
6 System.out.println( "After the call, x is " + x);
7 }
8
9 public static void increment( int n) {
10 n++;
11 System.out.println( "n inside the method is " + n);
12 }
13 }

invoke increment

increment n

Before the call, x is 1
n inside the method is 2
After the call, x is 1