When does things go wrong?

1. User Input → Enter invalid inputs
2. Device Errors → Printer jams, network connection drops.
3. Resource Limitations → Disk Full
4. Code Errors→ Invalid array index, key not present in hash table, refer to a variable that is null , divide by zero,…

• What can be an idea of signaling errors:
  • One way: Return an invalid value. Example → return -1 at end of file
  • But what if there is no obvious invalid value? → Example, return 0 (as false) if item is not found, but item can also be found at index 0.

Exception Handling

• Code that generates error is conventionally said to → raise an exception or throw an exception.
• Should also notify the type of error when raising this exception:
  • Information about the nature of the exception.
  • So it is natural to structure an exception as an object.
• Caller catches the exception and takes corrective action.
  • Extract information about the error from the exception object.
  • Graceful interruption rather than program crash.
• If caller does not catch the error:
  • It passes back up the calling chain → Error is passed to the person who called the caller.
• Declare if a method can throw an exception(raise an exception):
  • Compiler can then check whether the calling code has made some provisions to handle this exception.

Java’s Classification of Errors

<aside> 💡 All exceptions descend from the class Throwable.

</aside>

• Two branches from Throwable → Error and Exception.

1. Error → Relatively rare → Not the programmer’s fault.
   1. Internal errors, resource limitations within Java Runtime.
   2. No realistic correction action is possible, notify the caller and terminate gracefully.
2. Exception→ Has two sub branches.
   1. Runtime Exceptions and Checked Exceptions