Java Reference
In-Depth Information
Exception handling
enables a program to deal with exceptional situations and
continue its normal execution.
Key
Point
Runtime errors
occur while a program is running if the JVM detects an operation that is
impossible to carry out. For example, if you access an array using an index that is out of
bounds, you will get a runtime error with an
ArrayIndexOutOfBoundsException
. If you
enter a
double
value when your program expects an integer, you will get a runtime error with
an
InputMismatchException
.
In Java, runtime errors are thrown as exceptions. An
exception
is an object that represents
an error or a condition that prevents execution from proceeding normally. If the exception is
not handled, the program will terminate abnormally. How can you handle the exception so
that the program can continue to run or else terminate gracefully? This chapter introduces this
subject and text input and output.
exception
Exceptions are thrown from a method. The caller of the method can catch and handle
the exception.
Key
Point
To demonstrate exception handling, including how an exception object is created and thrown,
let's begin with the example in Listing 14.1, which reads in two integers and displays their
quotient.
VideoNote
Exception-handling
advantages
L
ISTING
14.1
Quotient.java
1
import
java.util.Scanner;
2
3
public class
Quotient {
4
public static void
main(String[] args) {
5 Scanner input =
new
Scanner(System.in);
6
7
// Prompt the user to enter two integers
8 System.out.print(
"Enter two integers: "
);
9
int
number1 = input.nextInt();
reads two integers
10
int
number2 = input.nextInt();
11
12 System.out.println(number1 +
" / "
+ number2 +
" is "
+
13 (
number1 / number2
));
integer division
14 }
15 }
5 2
Enter two integers:
5 / 2 is 2
Enter two integers:
Exception in thread "main" java.lang.ArithmeticException: / by zero
at Quotient.main(Quotient.java:11)
3 0
If you entered
0
for the second number, a runtime error would occur, because you cannot
divide an integer by
0
. (
Recall that a floating-point number divided by
0
does not raise an
exception.
) A simple way to fix this error is to add an
if
statement to test the second number,
as shown in Listing 14.2.
