• Recall Java Exceptions

Catching and Handling Exceptions

• try-catch

  • Enclose the code that may generate an exceptions in a try block.
  • To handle exception, write the code (say, Exception Handler) in the catch block.
  • Can see that it is very similar to Python.

  try{
  	...
  	//call a function that may throw an exception.
  	...
  }
  catch (ExceptionType e){
  	...
  	//examine the exception and handle accordingly.
  	...
  }
  

• If try encounters an exception, rest of the code in that block is skipped.

• If the exception matches the type in catch , handler code executes.

• What happens if type does not match? → Called Uncaught Exception

  • This exception is then passed back to the code that called this code.

• If no one who called the code catches (or handles) the code, it reaches the top level → Main

  • If main does not handle it → Program crashes

  ---

• We can catch more that one type of exception (that could be generated from the try block)

  • Use multiple catch blocks

  try{
  	//code that might throw some exception
  }
  catch(FileNotFoundException e){
  	//Handler code
  }
  catch(UnknownHostException e){
  	//Handler code
  }
  catch(IOException e){
  	//Handler Code
  }
  

<aside> 💡 Exception are classes in the Java class hierarchy.

</aside>

• Thus, catch (ExceptionType e) matches any subtype of ExceptionType

<aside> 💡 Catch blocks are tried in sequence.

</aside>

• Tries to match exception type against each one in turn.
• So naturally,
  • Order catch blocks by argument type from more specifc to less specific.

Generating Exceptions

When does a function generate an exception?

• One way: In case of Error type, (Refer Here) → JVM Runtime issue

• Another way: RuntimeException
  • Array index out of bounds, invalid hash key…