EXCEPTION HANDLING AND TEXT I/O - Introduction to Java Programming: Comprehensive Version - page 471

printStackTrace() ) in Exception are inherited from Throwable . The Exception
class contains four constructors. Among them, the following two constructors are often used:

java.lang.Exception

+Exception()
+Exception(message: String)

Constructs an exception with no message.
Constructs an exception with the specified message.

Line 6 invokes the superclass's constructor with a message. This message will be set in the
exception object and can be obtained by invoking getMessage() on the object.

Tip
Most exception classes in the Java API contain two constructors: a no-arg constructor
and a constructor with a message parameter.
To create an InvalidRadiusException , you have to pass a radius. There-
fore, the setRadius method in Listing 12.7 can be modified as shown in Listing 12.11.

L ISTING 12.11

TestCircleWithCustomException.java
1 public class TestCircleWithCustomException {
2

public static void main(String[] args) {

3 try {

4 new CircleWithCustomException( 5 );

5 new CircleWithCustomException( -5 );

6 new CircleWithCustomException( 0 );

7 }
8 catch (InvalidRadiusException ex) {
9 System.out.println(ex);
10 }
11
12 System.out.println( "Number of objects created: " +
13 CircleWithCustomException.getNumberOfObjects());
14 }
15 }
16
17 class CircleWithCustomException {
18 /** The radius of the circle */

19 private double radius;

20
21

/** The number of objects created */

22 private static int numberOfObjects = 0 ;

23
24 /** Construct a circle with radius 1 */

25 public CircleWithCustomException() throws InvalidRadiusException {

declare exception

26 this ( 1.0 );

27 }
28
29 /** Construct a circle with a specified radius */
30 public CircleWithCustomException( double newRadius)
31 throws InvalidRadiusException {
32 setRadius(newRadius);
33 numberOfObjects++;
34 }
35
36 /** Return radius */

37 public double getRadius() {