EXCEPTION HANDLING AND TEXT I/O - Introduction to Java Programming: Comprehensive Version - page 472

38 return radius;

39 }
40
41 /** Set a new radius */
42 public void setRadius( double newRadius)
43 throws InvalidRadiusException {
44 if (newRadius >= 0 )
45 radius = newRadius;
46 else

47 throw new InvalidRadiusException(newRadius); throw exception

48 }
49
50

/** Return numberOfObjects */

51 public static int getNumberOfObjects() {

52 return numberOfObjects;

53 }
54
55

/** Return the area of this circle */

56 public double findArea() {

57 return radius * radius * 3.14159 ;

58 }
59 }

InvalidRadiusException: Invalid radius -5.0
Number of objects created: 1

The setRadius method in CircleWithCustomException throws an InvalidRadius-
Exception when radius is negative (line 47). Since InvalidRadiusException is a
checked exception, the setRadius method must declare it in the method header (line 43).
Since the constructors for CircleWithCustomException invoke the setRadius method
to a set a new radius and it may throw an InvalidRadiusException , the constructors are
declared to throw InvalidRadiusException (lines 25, 31).
Invoking new CircleWithCustomException(-5) (line 5) throws an InvalidRadius-
Exception , which is caught by the handler. The handler displays the radius in the exception
object ex .

Tip
Can you define a custom exception class by extending RuntimeException ? Yes, but
it is not a good way to go, because it makes your custom exception unchecked. It is bet-
ter to make a custom exception checked, so that the compiler can force these exceptions
to be caught in your program.

checked custom exception

12.25 How do you define a custom exception class?
12.26 Suppose the setRadius method throws the InValidRadiusException defined in
Listing 12.10. What is displayed when the following program is run?

✓ ✓

Check

Point

public class Test {
public static void main(String[] args) {
try {
method();
System.out.println( "After the method call" );
}
catch (RuntimeException ex) {
System.out.println( "RuntimeException in main" );
}