listing 1

// Demonstrate exception handling.

class ExcDemo1 {

public static void main(String args[]) {

int nums[] = new int[4];

try {

System.out.println("Before exception is generated.");

// Generate an index out-of-bounds exception.

nums[7] = 10;

System.out.println("this won't be displayed");

}

catch (ArrayIndexOutOfBoundsException exc) {

// catch the exception

System.out.println("Index out-of-bounds!");

}

System.out.println("After catch statement.");

}

}

listing 2

/* An exception can be generated by one

method and caught by another. */

class ExcTest {

// Generate an exception.

static void genException() {

int nums[] = new int[4];

System.out.println("Before exception is generated.");

// generate an index out-of-bounds exception

nums[7] = 10;

System.out.println("this won't be displayed");

}

}

class ExcDemo2 {

public static void main(String args[]) {

try {

ExcTest.genException();

}

catch (ArrayIndexOutOfBoundsException exc) {

// catch the exception

System.out.println("Index out-of-bounds!");

}

System.out.println("After catch statement.");

}

}

listing 3

// Let JVM handle the error.

class NotHandled {

public static void main(String args[]) {

int nums[] = new int[4];

System.out.println("Before exception is generated.");

// generate an index out-of-bounds exception

nums[7] = 10;

}

}

listing 4

// This won't work!

class ExcTypeMismatch {

public static void main(String args[]) {

int nums[] = new int[4];

try {

System.out.println("Before exception is generated.");

// generate an index out-of-bounds exception

nums[7] = 10;

System.out.println("this won't be displayed");

}

/* Can't catch an array boundary error with an

ArithmeticException. */

catch (ArithmeticException exc) {

// catch the exception

System.out.println("Index out-of-bounds!");

}

System.out.println("After catch statement.");

}

}

listing 5

// Handle error gracefully and continue.

class ExcDemo3 {

public static void main(String args[]) {

int numer[] = { 4, 8, 16, 32, 64, 128 };

int denom[] = { 2, 0, 4, 4, 0, 8 };

for(int i=0; i<numer.length; i++) {

try {

System.out.println(numer[i] + " / " +

denom[i] + " is " +

numer[i]/denom[i]);

}

catch (ArithmeticException exc) {

// catch the exception

System.out.println("Can't divide by Zero!");

}

}

}

}

listing 6

// Use multiple catch statements.

class ExcDemo4 {

public static void main(String args[]) {

// Here, numer is longer than denom.

int numer[] = { 4, 8, 16, 32, 64, 128, 256, 512 };

int denom[] = { 2, 0, 4, 4, 0, 8 };

for(int i=0; i<numer.length; i++) {

try {

System.out.println(numer[i] + " / " +

denom[i] + " is " +

numer[i]/denom[i]);

}

catch (ArithmeticException exc) {

// catch the exception

System.out.println("Can't divide by Zero!");

}

catch (ArrayIndexOutOfBoundsException exc) {

// catch the exception

System.out.println("No matching element found.");

}

}

}

}

listing 7

// Subclasses must precede superclasses in catch statements.

class ExcDemo5 {

public static void main(String args[]) {

// Here, numer is longer than denom.

int numer[] = { 4, 8, 16, 32, 64, 128, 256, 512 };

int denom[] = { 2, 0, 4, 4, 0, 8 };

for(int i=0; i<numer.length; i++) {

try {

System.out.println(numer[i] + " / " +

denom[i] + " is " +

numer[i]/denom[i]);

}

catch (ArrayIndexOutOfBoundsException exc) {

// catch the exception

System.out.println("No matching element found.");

}

catch (Throwable exc) {

System.out.println("Some exception occurred.");

}

}

}

}

listing 8

// Use a nested try block.

class NestTrys {

public static void main(String args[]) {

// Here, numer is longer than denom.

int numer[] = { 4, 8, 16, 32, 64, 128, 256, 512 };

int denom[] = { 2, 0, 4, 4, 0, 8 };

try { // outer try

for(int i=0; i<numer.length; i++) {

try { // nested try

System.out.println(numer[i] + " / " +

denom[i] + " is " +

numer[i]/denom[i]);

}

catch (ArithmeticException exc) {

// catch the exception

System.out.println("Can't divide by Zero!");

}

}

}

catch (ArrayIndexOutOfBoundsException exc) {

// catch the exception

System.out.println("No matching element found.");

System.out.println("Fatal error -- program terminated.");

}

}

}

listing 9

// Manually throw an exception.

class ThrowDemo {

public static void main(String args[]) {

try {

System.out.println("Before throw.");

throw new ArithmeticException();

}

catch (ArithmeticException exc) {

// catch the exception

System.out.println("Exception caught.");

}

System.out.println("After try/catch block.");

}

}

listing 10

// Rethrow an exception.

class Rethrow {

public static void genException() {

// here, numer is longer than denom

int numer[] = { 4, 8, 16, 32, 64, 128, 256, 512 };

int denom[] = { 2, 0, 4, 4, 0, 8 };

for(int i=0; i<numer.length; i++) {

try {

System.out.println(numer[i] + " / " +

denom[i] + " is " +

numer[i]/denom[i]);

}

catch (ArithmeticException exc) {

// catch the exception

System.out.println("Can't divide by Zero!");

}

catch (ArrayIndexOutOfBoundsException exc) {

// catch the exception

System.out.println("No matching element found.");

throw exc; // rethrow the exception

}

}

}

}

class RethrowDemo {

public static void main(String args[]) {

try {

Rethrow.genException();

}

catch(ArrayIndexOutOfBoundsException exc) {

// recatch exception

System.out.println("Fatal error -- " +

"program terminated.");

}

}

}

listing 11

// Using the Throwable methods.

class ExcTest {

static void genException() {

int nums[] = new int[4];

System.out.println("Before exception is generated.");

// generate an index out-of-bounds exception

nums[7] = 10;

System.out.println("this won't be displayed");

}

}

class UseThrowableMethods {

public static void main(String args[]) {

try {

ExcTest.genException();

}

catch (ArrayIndexOutOfBoundsException exc) {

// catch the exception

System.out.println("Standard message is: ");

System.out.println(exc);

System.out.println("\nStack trace: ");

exc.printStackTrace();

}

System.out.println("After catch statement.");

}

}

listing 12

// Use finally.

class UseFinally {

public static void genException(int what) {

int t;

int nums[] = new int[2];

System.out.println("Receiving " + what);

try {

switch(what) {

case 0:

t = 10 / what; // generate div-by-zero error

break;

case 1:

nums[4] = 4; // generate array index error.

break;

case 2:

return; // return from try block

}

}

catch (ArithmeticException exc) {

// catch the exception

System.out.println("Can't divide by Zero!");

return; // return from catch

}

catch (ArrayIndexOutOfBoundsException exc) {

// catch the exception

System.out.println("No matching element found.");

}

finally {

System.out.println("Leaving try.");

}

}

}

class FinallyDemo {

public static void main(String args[]) {

for(int i=0; i < 3; i++) {

UseFinally.genException(i);

System.out.println();

}

}

}

listing 13

// Use throws.

class ThrowsDemo {

public static char prompt(String str)

throws java.io.IOException {

System.out.print(str + ": ");

return (char) System.in.read();

}

public static void main(String args[]) {

char ch;

try {

ch = prompt("Enter a letter");

}

catch(java.io.IOException exc) {

System.out.println("I/O exception occurred.");

ch = 'X';

}

System.out.println("You pressed " + ch);

}

}

listing 14

// Use the multi-catch feature. Note: This code requires JDK 7 or

// later to compiler.

class MultiCatch {

public static void main(String args[]) {

int a=88, b=0;

int result;

char chrs[] = { 'A', 'B', 'C' };

for(int i=0; i < 2; i++) {

try {

if(i == 0)

result = a / b; // generate an ArithmeticException

else

chrs[5] = 'X'; // generate an ArrayIndexOutOfBoundsException

// This catch clause catches both exceptions.

} catch(ArithmeticException |

ArrayIndexOutOfBoundsException e) {

System.out.println("Exception caught: " + e);

}

}

System.out.println("After multi-catch.");

}

}

listing 15

// Use a custom exception.

// Create an exception.

class NonIntResultException extends Exception {

int n;

int d;

NonIntResultException(int i, int j) {

n = i;

d = j;

}

public String toString() {

return "Result of " + n + " / " + d +

" is non-integer.";

}

}

class CustomExceptDemo {

public static void main(String args[]) {

// Here, numer contains some odd values.

int numer[] = { 4, 8, 15, 32, 64, 127, 256, 512 };

int denom[] = { 2, 0, 4, 4, 0, 8 };

for(int i=0; i<numer.length; i++) {

try {

if((numer[i]%2) != 0)

throw new

NonIntResultException(numer[i], denom[i]);

System.out.println(numer[i] + " / " +

denom[i] + " is " +

numer[i]/denom[i]);

}

catch (ArithmeticException exc) {

// catch the exception

System.out.println("Can't divide by Zero!");

}

catch (ArrayIndexOutOfBoundsException exc) {

// catch the exception

System.out.println("No matching element found.");

}

catch (NonIntResultException exc) {

System.out.println(exc);

}

}

}

}

listing 16

// An exception for queue-full errors.

public class QueueFullException extends Exception {

int size;

QueueFullException(int s) { size = s; }

public String toString() {

return "\nQueue is full. Maximum size is " +

size;

}

}

listing 17

// An exception for queue-empty errors.

public class QueueEmptyException extends Exception {

public String toString() {

return "\nQueue is empty.";

}

}

listing 18

/*

Try This 9-1

Add exception handling to the queue classes.

*/

// A fixed-size queue class for characters that uses exceptions.

class FixedQueue implements ICharQ {

private char q[]; // this array holds the queue

private int putloc, getloc; // the put and get indices

// Construct an empty queue given its size.

public FixedQueue(int size) {

q = new char[size]; // allocate memory for queue

putloc = getloc = 0;

}

// Put a characer into the queue.

public void put(char ch)

throws QueueFullException {

if(putloc==q.length)

throw new QueueFullException(q.length);

q[putloc++] = ch;

}

// Get a character from the queue.

public char get()

throws QueueEmptyException {

if(getloc == putloc)

throw new QueueEmptyException();

return q[getloc++];

}

}

listing 19

// Demonstrate the queue exceptions.

class QExcDemo {

public static void main(String args[]) {

FixedQueue q = new FixedQueue(10);

char ch;

int i;

try {

// overrun the queue

for(i=0; i < 11; i++) {

System.out.print("Attempting to store : " +

(char) ('A' + i));

q.put((char) ('A' + i));

System.out.println(" -- OK");

}

System.out.println();

}

catch (QueueFullException exc) {

System.out.println(exc);

}

System.out.println();

try {

// over-empty the queue

for(i=0; i < 11; i++) {

System.out.print("Getting next char: ");

ch = q.get();

System.out.println(ch);

}

}

catch (QueueEmptyException exc) {

System.out.println(exc);

}

}

}

listing 20

// A character queue interface that throws exceptions.

public interface ICharQ {

// Put a characer into the queue.

void put(char ch) throws QueueFullException;

// Get a character from the queue.

char get() throws QueueEmptyException;

}