Handling errors - Objects First with Java: A Practical Introduction Using BlueJ - page 431

An exception thrown from a constructor has the same effect on the client as an exception
thrown from a method. So the following attempt to create an invalid ContactDetails object
will completely fail; it will not result in a null value being stored in the variable:

ContactDetails badDetails = new ContactDetails("", "", "");

Code 12.7
The constructor of the
ContactDetails
class

/**
* Set up the contact details. All details are trimmed to remove
* trailing white space. Either name or phone must be non-blank.
* @param name The name.
* @param phone The phone number.
* @param address The address.
* @throws IllegalStateException If both name and phone are blank.
*/
public ContactDetails(String name, String phone, String address)
{
// Use blank strings if any of the parameters is null.
if (name == null ){
name = "" ;

}
if (phone == null ) {
phone = "" ;

}
if (address == null ) {
address = "" ;

}

this .name = name.trim();
this .phone = phone.trim();
this .address = address.trim();

if ( this .name.length() == 0 && this .phone.length() == 0) {
throw new IllegalStateException(
"Either the name or phone must not be blank." );

}

}

12.5 Exception handling

The principles of exception throwing apply equally to both unchecked and checked exceptions,
but the rules of Java mean that exception handling becomes a requirement only with checked
exceptions. A checked exception class is one that is a subclass of Exception but not of
RuntimeException . There are several more rules to follow when using checked exceptions,
because the compiler enforces checks both in a method that throws a checked exception and in
any caller of that method.