Download Handle Exceptions

Handle Exceptions
What is an Exception?
 An exception is an object that contains information about an error
that has occurred.
 When an error occurs in a method, the method throws an
exception.
 If an exception is thrown when you’re testing a console
application, some information about the exception, including its
name and stack trace, is displayed at the console.
 A stack trace is a list of the methods that were called before the
exception occurred. The list appears in reverse order, from the last
method called to the first method called.
 All exceptions are subclasses of the Exception class. The
Exception class represents the most general type of exception,
while the subclasses represent increasingly specific exceptions.
Murach’s Java SE 6, C5
© 2007, Mike Murach & Associates, Inc.
Slide 2
Some of the classes in the Exception hierarchy
Exception
RuntimeException
NoSuchElementException
InputMismatchException
IllegalArgumentException
NumberFormatException
ArithmeticException
NullPointerException
Scanner class’ next methods may throw
inputMitsmatchException if the data entered is
not the expected data type. For example,
nextDouble method gets text data.
Murach’s Java SE 6, C5
© 2007, Mike Murach & Associates, Inc.
Slide 3
Example of Exception
Exception in thread "main" java.util.InputMismatchException
at java.util.Scanner.throwFor(Scanner.java:840)
at java.util.Scanner.next(Scanner.java:1461)
at java.util.Scanner.nextDouble(Scanner.java:2387)
at testinstall.Main.main(Main.java:26)
Java Result: 1
BUILD SUCCESSFUL (total time: 10 seconds)
Using Try / Catch Statements to Handle Exceptions
The syntax for the try statement
try { statements }
catch(ExceptionClass exceptionName) { statements }
Two ways to import the InputMismatchException
class
import java.util.InputMismatchException;
import.java.util.*;
Murach’s Java SE 6, C5
© 2007, Mike Murach & Associates, Inc.
Slide 5
Try Catch: Typically work with a loop structure
Scanner sc=new Scanner(System.in);
try{
System.out.println("enter loan:");
double loan=sc.nextDouble();
System.out.println("enter rate in %:");
double rate=sc.nextDouble();
System.out.println("enter term in year:");
double term=sc.nextDouble();
double monPayment=(loan*rate/100/12)/(1-(Math.pow(1+rate/100/12,-12*term)));
System.out.println("Monthly payment is: =" + monPayment);
}
catch (InputMismatchException e)
{
sc.next();
System.out.println("Enter numeric data only");
}
System.out.println("Thank you for using payment calculator!");
Loan Calculator with Exception Handling
Scanner sc=new Scanner(System.in);
String flag="Y";
while (flag.equalsIgnoreCase("Y")){
try{
System.out.println("enter loan:");
double loan=sc.nextDouble();
System.out.println("enter rate in %:");
double rate=sc.nextDouble();
System.out.println("enter term in year:");
double term=sc.nextDouble();
double monPayment=(loan*rate/100/12)/(1-(Math.pow(1+rate/100/12,-12*term)));
System.out.println("Monthly payment is: =" + monPayment);
System.out.println("Do you want to continue? (Y/N):");
flag=sc.next();
}
catch (InputMismatchException e)
{
sc.next();
System.out.println("Enter numeric data only");
continue;
}
}
System.out.println("Thank you for using payment calculator!");
Methods of Exception Class
• catch (InputMismatchException e)
• catch (Exception e)
– Catch any exceptions
• System.out.println(e.getMessage());
• System.out.println(e.getStackTrace());
String Class Methods
• toLowerCase()
• toUpperCase()
• substring(int beginIndex)
– "unhappy".substring(2) returns "happy"
– 0-based index
• substring(int beginIndex, int endIndex)
– "hamburger".substring(4, 8) returns "urge"
"smiles".substring(1, 5) returns "mile"
• length()
• indexOf( char)
Full name format: First Name + Space + Last
Name
Change the Full Name to proper format where
the first letter of First Name and Last Name
changed to uppercase and other letters in
lower case
Example: “david chao” -> “David Chao”
Code Example
public static void main(String[] args) {
// TODO code application logic here
Scanner sc=new Scanner(System.in);
System.out.println("enter full name:");
String FullName=sc.nextLine();
int spaceIndex = FullName.indexOf(" ");
String firstName=FullName.substring(0,spaceIndex);
String lastName=FullName.substring(spaceIndex+1);
String newFullName=proper(firstName) + " " + proper(lastName);
System.out.println("Proepr full name:" + newFullName);
}
public static String proper(String Name){
return Name.substring(0,1).toUpperCase()+ Name.substring(1).toLowerCase();
}