SINGLE-DIMENSIONAL ARRAYS - Introduction to Java Programming: Comprehensive Version - page 258

Note
The preceding statement creates an array using the following syntax:

new elementType[]{value0, value1, ..., value k };

There is no explicit reference variable for the array. Such array is called an anonymous
array .

anonymous array

Java uses pass-by-value to pass arguments to a method. There are important differences
between passing the values of variables of primitive data types and passing arrays.

pass-by-value

For an argument of a primitive type, the argument's value is passed.

■

For an argument of an array type, the value of the argument is a reference to an array;
this reference value is passed to the method. Semantically, it can be best described as
pass-by-sharing , that is, the array in the method is the same as the array being passed.
Thus, if you change the array in the method, you will see the change outside the method.

■

pass-by-sharing

Take the following code, for example:

public class Test {
public static void main(String[] args) {
int x = 1 ; // x represents an int value
int [] y = new int [ 10 ]; // y represents an array of int values

m(x, y); // Invoke m with arguments x and y

System.out.println( "x is " + x);
System.out.println( "y[0] is " + y[ 0 ]);
}

public static void m( int number, int [] numbers) {
number = 1001 ; // Assign a new value to number
numbers[ 0 ] = 5555 ; // Assign a new value to numbers[0]
}
}

x is 1
y[0] is 5555

You may wonder why after m is invoked, x remains 1 , but y[0] become 5555 . This is
because y and numbers , although they are independent variables, reference the same array, as
illustrated in Figure 7.5. When m(x, y) is invoked, the values of x and y are passed to num-
ber and numbers . Since y contains the reference value to the array, numbers now contains
the same reference value to the same array.

Stack Heap

Activation record for
method m
int[] numbers:
int number: 1

reference

Arrays are
stored in a
heap.

An array of
ten int
values is
stored here

Activation record for the
main method
int[] y :
int x :1

reference

F IGURE 7.5

The primitive type value in x is passed to number , and the reference value in y
is passed to numbers .