ARRAYS - Java Programming: From Problem Analysis to Program Design - page 576

Arrays of Objects of Other Classes
This section discusses, in general, how to create and work with an array of objects.
Suppose that you have 100 employees who are paid on an hourly basis, and you need to
keep track of their arrival and departure times. In Chapter 8, we designed and imple-
mented the class Clock to implement the time of day in a program. You can declare
two arrays— arrivalTimeEmp and departureTimeEmp —of 100 elements each,
wherein each element is a reference variable of Clock type. Consider the following
statement:

Clock[] arrivalTimeEmp = new Clock[100]; //Line 1

The statement in Line 1 creates the array shown in Figure 9-12.

arrivalTimeEmp

arrivalTimeEmp[0]

.
.
.

arrivalTimeEmp[49]

.
.
.

arrivalTimeEmp[99]

FIGURE 9-12 Array arrivalTimeEmp

The statement in Line 1 creates only the array, not the objects arrivalTimeEmp[0] ,
arrivalTimeEmp[1] ,..., arrivalTimeEmp[99] . We still need to instantiate Clock
objects for each array element. Consider the following statements:

for ( int j = 0; j < arrivalTimeEmp.length; j++) //Line 2
arrivalTimeEmp[j] = new Clock(); //Line 3
The statements in Lines 2 and 3 instantiate the objects arrivalTimeEmp[0] ,
arrivalTimeEmp[1] ,..., arrivalTimeEmp[99] , as shown in Figure 9-13.