Declarations, Initialization, and Scoping - SCJP Sun Certified Programmer for Java Platform SE6 - page 90

Array Objects

Because a Java array is an object, it should be no surprise that you use the new keyword to
instantiate an array. The new keyword requires the type of array being instantiated along
with the size of the array. For example, the following code instantiates three array objects:

5. int [] finishTimes = new int[20];
6. String lastNames [] = new String[100];
7. GregorianCalendar [] july;
8. july = new GregorianCalendar[31];

The finishTimes reference now points to an array of 20 ints . Because this array of
ints is a new object, its memory is zeroed on the heap, so all 20 ints are initially 0 . The
lastNames reference points to an array of 100 String references (not String objects!).
Each of the 100 String references is null . Similarly, july points to an array of 31 null
GregorianCalendar references. Arrays in Java are zero-based indexed, meaning the fi rst
element in the array is index 0, the second element is index 1, and so on. For example, the
following code is valid and initializes some of the values in the arrays:

10. finishTimes[0] = 1002892;
11. finishTimes[1] = 1004830;
12. lastNames[99] = “Washington”;
13. july[0] = new GregorianCalendar(2010, 7, 1);

Figure 2.3 shows what the finishTimes and lastNames arrays look like in memory;
Figure 2.4 shows what the july array looks like in memory.

FIGURE 2.3 Examples of array references pointing to array objects.

0
1
2
3
.
.
19

1002892
0
0
0
.
.
0

array object of
20 ints

finishTimes

array references

null
null
null
null

0
1
2
3
.
.
99

lastNames

array object of 100
String references

“Washington”

A String Object