Exception Handling - Beginning Java 8 Fundamentals - page 335

The output of Listing 9-2 is nicer than that of Listing 9-1. It tells you exactly what happened when the program
was executed. Notice that the program did not terminate when the exception occurred because you handled the
exception. The program executed the last statement that printed the “At the end of the program” message.

Transfer of Control
You need to understand very precisely the flow of control when an exception is thrown in a try block. First, the Java
runtime creates an object of the appropriate class to represent the exception that has occurred. The first catch block
following the try block is checked. If the exception object can be assigned to the parameter for the catch block, the
parameter of the catch block is assigned the reference of the exception object, and the control is transferred to the
body of the catch block. When the catch block finishes executing its body, the control is transferred to the point
following the try-catch block. It is very important to note that after executing the catch block the control is not
transferred back to the try block. Rather, it is transferred to the code that follows the try-catch block. If a try block
has many catch blocks associated with it, a maximum of one catch block is executed. Figure 9-1 shows the transfer of
control in a typical Java program when an exception occurs in a try block.

Some statements go here...
try {

try-statement-1;
try-statement-2;
try-statement-3;

}
catch(Exception1 e1) {
catch-statement-11;
catch-statement-12;

}
catch(Exception2 e2) {
catch-statement-21;
catch-statement-22;

}
catch(Exception3 e3) {
catch-statement-31;
catch-statement-32;

}

statement-1;
more statements go here...

Figure 9-1. Transfer of control when an exception occurs in a try block

You assume that when try-statement-2 is executed, it throws an exception of type Exception2 . When the
exception is thrown, the control is transferred to the second catch block, and catch-statement-21 and
catch-statement-22 are executed. After catch-statement-22 is executed, control is transferred outside the try-
catch block, and statement-1 starts executing. It is very important to understand that try-statement-3 is never
executed when try-statement-2 throws an exception. Among three catch blocks, a maximum of one will be
executed when a statement inside the try block throws an exception.

Exception Class Hierarchy
The Java class library contains many exception classes. Figure 9-2 shows a few exception classes. Note that the Object
class does not belong to the family of exception classes. It is shown in the figure as an ancestor of the Throwable class
in the inheritance hierarchy.