Java handles two types of exceptions - unchecked exceptions and checked exceptions. Unchecked exceptions do not need to be handled by programmers, while checked exceptions must be handled. Checked exceptions are environment or server-related issues outside a programmer's control. There are three ways to handle checked exceptions: try-catch blocks, throwing exceptions with the throw keyword, or specifying exceptions with the throws keyword in method signatures. Finally blocks are used to ensure cleanup code executes after try or catch blocks complete.

1. Exceptions
Java handles two types of exceptions.
Unchecked exceptions and checked exceptions
Checked and unchecked
For unchecked exceptions, programmers need not to handle the exceptions. .i.e. optional
For checked exceptions programmers have to handle exceptions.
Unchecked exceptions are of two groups.
>> Errors
>> Runtime exceptions
Standard java classes. Inheriting an error class or runt time exception class
Unchecked exception
Logical mistakes which can be corrected by the programmer. It doesn’t have to be thrown/
caught by the method.
Example of unchecked exception
int div (int a, int b)
{
Return (a/b);
}
int div() {
int num = Integer.ParseInt (args[]);
int result = 4 / num;
}
The above throws Arithmetic Exception, ArrayIndexOutOfBounds Exception and
NumberFormatException
Examples
For errors,
Internal error
No such method error
No such field error
Illegal access error
Run time exceptions
Null pointer exception
Array index out of bound exception
Checked
Exceptions which are environment or server related and which are beyond the control of the
programmers. These exceptions need to be caught by three ways.
Connection Refused – Related to DB
BindException = Previous running server current session cannot be joined

2. IllegalStateException = Server not started
Exception
Exception hierarchy
Throwable
_|_
Error/RTE
Exception
|
|
Unchecked
Checked
Types of exception handling
 Try catch
 Defer using throw or throws
throws is attached next to the method which potentially throws checked exception; We can also
actually do the logic and find where exactly the exception is thrown and use the throw keyword
which is like return keyword which returns the Exception object.
What is the sequence of catch block?
First catch the child exception and then parent exception
Finally block
It is used along with try catch. Java executes finally block after try block or catch block
Note – Clean up code is generally written into the finally block.
Sample Code done in class
package com.canvas.dec12;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.util.Properties;
public class LearningErrorHandling {
/**
* @param args
* @throws Throwable
*/
public static void main(String[] args) throws Throwable {
// TODO Auto-generated method stub
Properties pr=new Properties();
FileInputStream fi=new FileInputStream("c:logg.properties");
convertStringToDouble("100.5");

3. }
public static void convertStringToDouble(String s){
//try-catch
double myd=0.0;
try{
myd=Double.parseDouble(s);
System.out.println("this is the line after converting to double");
}catch(Throwable t){
System.out.println("this is the catch block");
}
System.out.println("this is the value of myd----"+myd);
}
}