JAVA TUTORIALS - Java - Exceptions
Java - Exceptions
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Exceptions Methods:
SN | Methods with Description |
---|---|
1 | public String getMessage() Returns a detailed message about the exception that has occurred. This message is initialized in the Throwable constructor. |
2 | public Throwable getCause() Returns the cause of the exception as represented by a Throwable object. |
3 | public String toString() Returns the name of the class concatenated with the result of getMessage() |
4 | public void printStackTrace() Prints the result of toString() along with the stack trace to System.err, the error output stream. |
5 | public StackTraceElement [] getStackTrace() Returns an array containing each element on the stack trace. The element at index 0 represents the top of the call stack, and the last element in the array represents the method at the bottom of the call stack. |
6 | public Throwable fillInStackTrace() Fills the stack trace of this Throwable object with the current stack trace, adding to any previous information in the stack trace. |
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Catching Exceptions:
try { //Protected code }catch(ExceptionName e1) { //Catch block }ADVERTISEMENTSExample:
// File Name : ExcepTest.java import java.io.*; public class ExcepTest{ public static void main(String args[]){ try{ int a[] = new int[2]; System.out.println("Access element three :" + a[3]); }catch(ArrayIndexOutOfBoundsException e){ System.out.println("Exception thrown :" + e); } System.out.println("Out of the block"); } }
Exception thrown :java.lang.ArrayIndexOutOfBoundsException: 3 Out of the blockMultiple catch Blocks:
try { //Protected code }catch(ExceptionType1 e1) { //Catch block }catch(ExceptionType2 e2) { //Catch block }catch(ExceptionType3 e3) { //Catch block }Example:
try { file = new FileInputStream(fileName); x = (byte) file.read(); }catch(IOException i) { i.printStackTrace(); return -1; }catch(FileNotFoundException f) //Not valid! { f.printStackTrace(); return -1; }The throws/throw Keywords:
import java.io.*; public class className { public void deposit(double amount) throws RemoteException { // Method implementation throw new RemoteException(); } //Remainder of class definition }
import java.io.*; public class className { public void withdraw(double amount) throws RemoteException, InsufficientFundsException { // Method implementation } //Remainder of class definition }The finally Keyword
try { //Protected code }catch(ExceptionType1 e1) { //Catch block }catch(ExceptionType2 e2) { //Catch block }catch(ExceptionType3 e3) { //Catch block }finally { //The finally block always executes. }Example:
public class ExcepTest{ public static void main(String args[]){ int a[] = new int[2]; try{ System.out.println("Access element three :" + a[3]); }catch(ArrayIndexOutOfBoundsException e){ System.out.println("Exception thrown :" + e); } finally{ a[0] = 6; System.out.println("First element value: " +a[0]); System.out.println("The finally statement is executed"); } } }
Exception thrown :java.lang.ArrayIndexOutOfBoundsException: 3 First element value: 6 The finally statement is executedDeclaring you own Exception:
class MyException extends Exception{ }Example:
// File Name InsufficientFundsException.java import java.io.*; public class InsufficientFundsException extends Exception { private double amount; public InsufficientFundsException(double amount) { this.amount = amount; } public double getAmount() { return amount; } }
// File Name CheckingAccount.java import java.io.*; public class CheckingAccount { private double balance; private int number; public CheckingAccount(int number) { this.number = number; } public void deposit(double amount) { balance += amount; } public void withdraw(double amount) throws InsufficientFundsException { if(amount <= balance) { balance -= amount; } else { double needs = amount - balance; throw new InsufficientFundsException(needs); } } public double getBalance() { return balance; } public int getNumber() { return number; } }
// File Name BankDemo.java public class BankDemo { public static void main(String [] args) { CheckingAccount c = new CheckingAccount(101); System.out.println("Depositing $500..."); c.deposit(500.00); try { System.out.println("\nWithdrawing $100..."); c.withdraw(100.00); System.out.println("\nWithdrawing $600..."); c.withdraw(600.00); }catch(InsufficientFundsException e) { System.out.println("Sorry, but you are short $" + e.getAmount()); e.printStackTrace(); } } }
Depositing $500... Withdrawing $100... Withdrawing $600... Sorry, but you are short $200.0 InsufficientFundsException at CheckingAccount.withdraw(CheckingAccount.java:25) at BankDemo.main(BankDemo.java:13)