Arrays - Java - page 338

Display 6.1 An Array Used in a Program (part 2 of 2)

A Common Way to Visualize an Array:

Indices

0 1 2 3 4

80 99.9 75 100 85.5

score[3]

The array score

The third use of square brackets is to name an indexed variable of the array, such as
score[0] or score[3] , as illustrated by the following line:

max = score[0];

As we mentioned previously, the integer inside the square brackets can be any
expression that evaluates to a suitable integer, as illustrated by the following:
int next = 1;
score[next + 3] = 100;
System.out.println(
"Score at position 4 is " + score[next + 3]);

Note that, in the preceding code, score[next + 3] and score[4] are the same
indexed variable, because next + 3 evaluates to 4 .

The length Instance Variable
In Java an array is considered to be an object, and, like other objects, it might
have instance variables. As it turns out, an array has only one public instance
variable, which is named length . The instance variable length is automatically set
to the size of the array when the array is created. For example, if you create an
array as follows,

double [] score = new double [5];

then score.length has a value of 5 .
The length instance variable can be used to make your program clearer by replac-
ing an unnamed constant, such as 5 , whose meaning may not be obvious, with a
meaningful name like score.length . In Display 6.2 we have rewritten the program in
Display 6.1 using the length instance variable.