Java The Complete Reference, Seventh Edition

212 Part I: The Java Language

c[42] = 99; // generate an out-of-bounds exception

}

} catch(ArrayIndexOutOfBoundsException e) {

System.out.println("Array index out-of-bounds: " + e);

}

} catch(ArithmeticException e) {

System.out.println("Divide by 0: " + e);

}

}

}

As you can see, this program nests onetryblock within another. The program works as

follows. When you execute the program with no command-line arguments, a divide-by-zero

exception is generated by the outertryblock. Execution of the program with one command-line

argument generates a divide-by-zero exception from within the nestedtryblock. Since the

inner block does not catch this exception, it is passed on to the outertryblock, where it is

handled. If you execute the program with two command-line arguments, an array boundary

exception is generated from within the innertryblock. Here are sample runs that illustrate

each case:

C:\>java NestTry

Divide by 0: java.lang.ArithmeticException: / by zero

C:\>java NestTry One

a = 1

Divide by 0: java.lang.ArithmeticException: / by zero

C:\>java NestTry One Two

a = 2

Array index out-of-bounds:

java.lang.ArrayIndexOutOfBoundsException:42

Nesting oftrystatements can occur in less obvious ways when method calls are involved.

For example, you can enclose a call to a method within atryblock. Inside that method is

anothertrystatement. In this case, thetrywithin the method is still nested inside the outertry

block, which calls the method. Here is the previous program recoded so that the nested

tryblock is moved inside the methodnesttry( ):

/* Try statements can be implicitly nested via

calls to methods. */

class MethNestTry {

static void nesttry(int a) {

try { // nested try block

/* If one command-line arg is used,

then a divide-by-zero exception

will be generated by the following code. */

if(a==1) a = a/(a-a); // division by zero