Handling Exceptions and Debugging - Beginning Java Programming: The Object-Oriented Approach - page 183

int age;
Person (){
}
}
You probably expect this to lead to a null pointer exception at line 12 now, because you never
initialized the name or age of the Person object referenced by employee . However, if you run this
code, the following line is output to the console: null is 0 years old. This is because Java will
automatically initialize fields of an object to a default value, null for objects and 0 for int , and it is
possible to print these values.
You might be wondering then, how a null pointer exception comes up, aside from actually ini-
tializing a variable to null. One way this can happen, shown in the following code, is when a second
object type JobType is added and a Person object is assigned a JobType object.
public class ExceptionExamples {
public static void main(String[] args) {
Person employee = new Person();
printPerson(employee);
}
public static void printPerson(Person myPerson){
System.out.println(myPerson.name + " is " + myPerson.age +
" years old and works as a " + myPerson.job.JobName);
}
}
class Person{
String name;
int age;
JobType job;
Person (){
}
}
class JobType{
String JobName;
int salaryBand;
JobType (){
}
}