debugging.md

Class video 2.4

• reading an error stacktrace
• common exception you will encounter
  • ArrayIndexOutBoundsException
    • python: list index out of range
  • StringIndexOutOfBoundsException
  • NullPointerException
    • python: TypeError (invalid type such as NoneType) or ValueError (correct type, but the value is outside of the accepted domain)

Debugging with stacktrace

• a sequence of method calls

Where to begin the debugging process

• read the stacktrace top to bottom
• find the first line of code that you wrote
• exceptions "bubble up". More on this later
• some exception have self explanatory names
  • ArrayIndexOutBoundsException
  • ArithmeticException
• pay attention to any extra information being provided by the stacktrace

NullPointerException

• one of the most common errors your see
• occurs when you are trying to access a method or instance variable from an object that is null.
• usually caused by
  • forgetting to call a constructor to first create the object
  • if you have a collection of data, then accessing beyond the first or last element of data.

Class video 2.5

• debugging using the eclipse debugger
  • breakpoints
  • stepping into and over a method
  • the display

In most of cases, we write a simple print state

print("I am here")

However, people usually forget to remove debugging the print statement.

step into

will jump into next step, will go to other block of code

step return

will return into previous step

step over

remain in the same block, move to next line