Java Reference
In-Depth Information
When you are working with this sample array, if you attempt to refer to
list[-1]
or
list[5]
, you are attempting to access an array element that does not exist. If
your code makes such an illegal reference, Java will halt your program with an
ArrayIndexOutOfBoundsException
.
Let's look at a program in which an array allows you to solve a problem that you
couldn't solve before. If you tune in to any local news broadcast at night, you'll hear
them report the high temperature for that day. It is usually reported as an integer, as
in, “It got up to 78 today.”
Suppose you want to examine a series of daily high temperatures, compute the
average high temperature, and count how many days were above that average temper-
ature. You've been using
Scanner
s to solve problems like this, and you can almost
solve the problem that way. If you just wanted to know the average, you could use a
Scanner
and write a cumulative sum loop to find it:
1 // Reads a series of high temperatures and reports the average.
2
3
import
java.util.*;
4
5
public class
Temperature1 {
6
public static void
main(String[] args) {
7 Scanner console =
new
Scanner(System.in);
8 System.out.print("How many days' temperatures? ");
9
int
numDays = console.nextInt();
10
int
sum = 0;
11
for
(
int
i = 1; i <= numDays; i++) {
12 System.out.print("Day " + i + "'s high temp: ");
13
int
next = console.nextInt();
14 sum += next;
15 }
16
double
average = (
double
) sum / numDays;
17 System.out.println();
18 System.out.println("Average = " + average);
19 }
20 }
Did You Know?
Buffer Overruns
One of the earliest and still most common sources of computer security problems
is a
buffer overrun
(also known as a
buffer overflow
). A buffer overrun is similar
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