Java 天地·Core Java·Lecture Notes·Unitt5 - Array and Strings

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Content Page # 13

Array bounds exceptions

An error will occur if an index is given for an array, which is either negative, or greater than the index of the last element of the array (i.e. a value of <array>.lengthor greater). Such an error is called an array bounds exception.

The program must not attempt to read or change the value of an array element that does not exist. For example, no array can have an element whose index is less than zero

Suppose we define an array of doubles like this:

double myArray[] = new double[100];

Then all the following lines will cause a run time error (that is, the program will compile correctly, but when executed will stop with an error message):

myArray[] = 0;
myArray[100] = 0;
myArray[1000] = 0;
int y = -1;
myArray[y] = 0;

Note that the compiler does not detect these errors; the error is not noted until the program is executed. This is true even of the first line, which is manifestly incorrect.

Consider the following application:

class ArrayBoundsException
{
double myArray[] = new double[100];
public static void main( String args[] )
{
ArrayBoundsException app = new ArrayBoundsException();
}
ArrayBoundsException()
{
myArray[-1] = 0;
}
}

The error displayed when this application is run as follows:

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