Data Structures and Algorithms in Java[1].pdf - Fulvio Frisone

the array, we will sometimes refer to the length of an array as its capacity. We show
another simple use of an array in the following code fragment, which counts the
number of times a certain number appears in an array:
/** Counts the number of times an integer appears in
an array. */
public static int findCount(int[] a, int k) {
int count = 0;
for (int e: a) {
// note the use of the "foreach" loop
}
if (e == k) // check if the current element equals k
count++;
return count;
}
Out of Bounds Errors
It is a dangerous mistake to attempt to index into an array a using a number outside
the range from 0 to a.length − 1. Such a reference is said to be out of
bounds. Out of bounds references have been exploited numerous times by hackers
using a method called the buffer overflow attack to compromise the security of
computer systems written in languages other than Java. As a safety feature, array
indices are always checked in Java to see if they are ever out of bounds. If an array
index is out of bounds, the run-time Java environment signals an error condition.
The name of this condition is the ArrayIndexOutOfBoundsException. This
check helps Java avoid a number of security problems (including buffer overflow
attacks) that other languages must cope with.
We can avoid out-of-bounds errors by making sure that we alway index into an
array, a, using an integer value between 0 and a.length. One shorthand way we
can do this is by carefully using the early termination feature of Boolean operations
in Java. For example, a statement like the following will never generate an index
out-of-bounds error:
if ((i >= 0) && (i < a.length) && (a[i] > 2) )
× = a[i];
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