Exception Handling

Multiple catch Blocks

In some cases, a method may have to catch different types of exceptions. Java supports multiple catch blocks. Each catch block must specify a different type of exception:

try
{
// method calls go here
}
catch( SomeExceptionClass e )
{
// handle SomeExceptionClass exceptions here
}
catch( SomeOtherExceptionClass e )
{
// handle SomeOtherExceptionClass exceptions here
}

When an exception is thrown in the try block, it is caught by the first catch block of the appropriate type.

A method that ignores exceptions thrown by the method it calls.

import java.io.* ;
import java.lang.Exception ;
public class MultiThrow
{
public static void main( String[] args )
{
try
{
fool() ;
}
catch( Exception e )
{
System.out.println( "Caught exception " +
e.getMessage() ) ;
}
}
static void fool() throws Exception
{
bar() ;
}
static void bar() throws Exception
{
throw new Exception( "Who cares" ) ;
}
}

Output

In the example main() calls fool() which calls bar(). Because bar() throws an exception and doesn't catch it, fool() has the opportunity to catch it. The fool() method has no catch block, so it cannot catch the exception. In this case, the exception propagates up the call stack to fool()'s caller, main().

A method that catches and rethrows an exception.

import java.io.* ;
import java.lang.Exception ;
public class MultiThrowA
{
public static void main( String[] args )
{
try
{
fool() ;
}
catch( Exception e )
{
System.out.println( "Caught exception " +
e.getMessage() ) ;
}
} static void fool() throws Exception
{
try
{
bar() ;
}
catch( Exception e )
{
System.out.println( "Re throw exception -- " +
e.getMessage() ) ;
throw e ;
}
}
static void bar() throws Exception
{
throw new Exception( "Who cares" ) ;
}
}

Output

The fool() method calls bar(). The bar() method throws an exception and fool() catches it. In the example, fool() simply rethrows the exception, which is ultimately caught in the application's main() method. In a real application, fool() could do some processing and then rethrow the exception. This arrangement allows both fool() and main() to handle the exception.