Two Ways to Create Arrays
With Initial Values
int[] scores = {85, 92, 78, 95, 88};
Values filled in at creation
With Fixed Size (empty)
int[] scores = new int[5];
int defaults to 0String Array (empty)
String[] names = new String[3];
String defaults to nullInteractive Array Explorer
int[] ages = {63, 65, 60, 53, 58, 37, 35, 31};
Click any cell to inspect it
Click a cell to see its access expression
ages.length returns 8
Last valid index = length - 1 = 7
Common Operations
Read a Value
Enter an index and click Read
Write a Value
Enter an index and value, then click Write
The Off-by-One Trap
What happens when you access ages[8] on an 8-element array?
Exception in thread "main"
java.lang.ArrayIndexOutOfBoundsException: Index 8 out of bounds for length 8
java.lang.ArrayIndexOutOfBoundsException: Index 8 out of bounds for length 8
Rule: Valid indices are
0 to length - 1. For an 8-element array, that means 0 through 7.
Looping Through an Array
for (int i = 0; i < ages.length; i++) {
System.out.println(ages[i]);
}
Warning: Always use
< length, never <= length! The last valid index is length - 1.
Tip: Arrays have a FIXED size. Once created, you cannot add or remove elements. We will learn about
ArrayList later — it can grow and shrink.