Java Reference
In-Depth Information
Runtime exceptions
are represented in the
RuntimeException
class, which
describes programming errors, such as bad casting, accessing an out-of-bounds
array, and numeric errors. Runtime exceptions are generally thrown by the JVM.
Examples of subclasses are listed in Table 14.3.
runtime exception
■
T
ABLE
14.3
Examples of Subclasses of
RuntimeException
Class
Reasons for Exception
ArithmeticException
Dividing an integer by zero. Note that floating-point arithmetic
does not throw exceptions (see Appendix E, Special Floating-
Point Values).
Attempt to access an object through a
null
reference variable.
NullPointerException
IndexOutOfBoundsException
Index to an array is out of range.
IllegalArgumentException
A method is passed an argument that is illegal or inappropriate.
RuntimeException
,
Error
, and their subclasses are known as
unchecked exceptions
. All
other exceptions are known as
checked exceptions
, meaning that the compiler forces the
programmer to check and deal with them in a
try-catch
block or declare it in the method
header. Declaring an exception in the method header will be covered in Section 14.4.
In most cases, unchecked exceptions reflect programming logic errors that are unrecover-
able. For example, a
NullPointerException
is thrown if you access an object through a
reference variable before an object is assigned to it; an
IndexOutOfBoundsException
is
thrown if you access an element in an array outside the bounds of the array. These are logic
errors that should be corrected in the program. Unchecked exceptions can occur anywhere in
a program. To avoid cumbersome overuse of
try-catch
blocks, Java does not mandate that
you write code to catch or declare unchecked exceptions.
unchecked exception
checked exception
✓
✓
Check
14.7
Describe the Java
Throwable
class, its subclasses, and the types of exceptions.
14.8
What
RuntimeException
will the following programs throw, if any?
Point
public class
Test {
public static void
main(String[] args) {
System.out.println(
1
/
0
);
public class
Test {
public static void
main(String[] args) {
int
[] list =
new int
[
5
];
System.out.println(list[
5
]);
}
}
}
}
(a)
(b)
public class
Test {
public static void
main(String[] args) {
String s =
"abc"
;
System.out.println(s.charAt(
3
));
public class
Test {
public static void
main(String[] args) {
Object o =
new
Object();
String d = (String)o;
}
}
}
}
(c)
(d)
public class
Test {
public static void
main(String[] args) {
System.out.println(
1.0
/
0
);
public class
Test {
public static void
main(String[] args) {
Object o =
null
;
System.out.println(o.toString());
}
}
}
}
(e)
(f)
