SINGLE-DIMENSIONAL ARRAYS - Introduction to Java Programming: Comprehensive Version - page 260

As shown in Figure 7.6, the two elements are not swapped using the swap method. However,
they are swapped using the swapFirstTwoInArray method. Since the parameters in the
swap method are primitive type, the values of a[0] and a[1] are passed to n1 and n2 inside
the method when invoking swap(a[0], a[1]) . The memory locations for n1 and n2 are
independent of the ones for a[0] and a[1] . The contents of the array are not affected by
this call.

Stack Heap Stack

Activation record for the
swapFirstTwoInArray
method

Activation record for
the swap method

int[] array

reference

n2 :2
n1 :1

Activation record for
the main method

Activation record for the
main method
int[] a int[] a reference

reference

a[0] :1
a[1] :2

Invoke swap(int n1, int n2) .
The primitive type values in
a[0] and a[1] are passed to the
swap method.

Invoke swapFirstTwoInArray(int[]
array) . The reference value in a is passed
to the swapFirstTwoInArray method.

The arrays are
stored in a
heap.

F IGURE 7.6

When passing an array to a method, the reference of the array is passed
to the method.

The parameter in the swapFirstTwoInArray method is an array. As shown in Figure 7.6,
the reference of the array is passed to the method. Thus the variables a (outside the method)
and array (inside the method) both refer to the same array in the same memory location.
Therefore, swapping array[0] with array[1] inside the method swapFirstTwoInArray
is the same as swapping a[0] with a[1] outside of the method.

7.7 Returning an Array from a Method
When a method returns an array, the reference of the array is returned.

Key
Point

You can pass arrays when invoking a method. A method may also return an array. For exam-
ple, the following method returns an array that is the reversal of another array.

l public static int [] reverse( int [] list) {
2

int [] result = new int [list.length];

create array

3
4 for ( int i = 0 , j = result.length - 1 ;
5 i < list.length; i++, j--) {
6 result[j] = list[i];
7}
8
9

list

return array return result;

result

10 }

Line 2 creates a new array result . Lines 4-7 copy elements from array list to array
result . Line 9 returns the array. For example, the following statement returns a new array
list2 with elements 6 , 5 , 4 , 3 , 2 , 1 .

int [] list1 = { 1 , 2 , 3 , 4 , 5 , 6 };
int [] list2 = reverse(list1);